Intrapartum Ultrasonography for Labor Management: Labor, Delivery and Puerperium

By Antonio Malvasi

This updated book is a practical guide to intrapartum ultrasonography to help practitioners improve labor and delivery, and to limit, where possible, complications.

Presenting the authors’ experiences, the book summarizes the state of the art in normal and abnormal labor. It clearly documents the use of intrapartum ultrasonography to evaluate the first and second stages of labor and diagnose the occiput posterior and transverse positions. Each situation is analyzed with the help of numerous informative images and invaluable tips and tricks showing how fetal head engagement and progression can be documented objectively. The importance of ultrasound in obstetrics risk management is also addressed.

Explaining how intrapartum ultrasonography can be used to assess whether a safe natural delivery is likely or whether operative procedures are required, the book is a valuable resource for all professionals – physicians and midwifes alike – caring for women in labor.

• Language: English
• Publisher: Springer
• Release date: Jan 4, 2021
• ISBN: 9783030575953

Book preview

Part ISonographic Anatomy of the Uterus

© Springer Nature Switzerland AG 2021

A. Malvasi (ed.)Intrapartum Ultrasonography for Labor Managementhttps://doi.org/10.1007/978-3-030-57595-3_1

1. From the Blind Twentieth-Century Obstetrics to an Ultrasound Twenty-First-Century Obstetrics

Olivier Dupuis¹  

(1)

Lyon University, Lyon, France

Olivier Dupuis

Email: [e-mail]

Sunday, March 27, 1977, 5 PM, at Los Rodeos Airport in the Canary Island, two 747 Boeings—the 747 was considered as the safest aircraft at that time—are about to take off [1].

Fog appears, and rapidly the visibility decreases to 300 m, the air traffic controllers (ATC) lose sights of the airplanes, the fog still increases, and soon on board the planes, passengers are unable to see airplane engines on the wings.

At 5.05 PM, ATC orders the Pan Am 747 to leave the runway using the third taxiway, but due to the fog, the pilots are unable to see the taxiway and continue straight ahead onto the runway.

At 5.06 PM, the KLM Boeing captain applies full throttle, while 1400 meters straight ahead stands the Pan Am Boeing.

At 5.06, the two airplanes collide causing the worst Civil Crash ever and killing 583 persons.

In Europe, in the operating theatre of the X Clinic, a gynaecological surgeon is going to perform a simple ovarian cystectomy under laparoscopy. General anaesthesia has been performed, and the bladder has been catheterized all under a correct asepsis. The surgeon inserts the Veress needle blindly into the abdomen. In the following seconds, the anaesthetist announces that he is no longer able to record the patient’s blood pressure. At the same moment, the surgeon introducing his optical device sees a full red screen. Immediately, he performs a midline laparotomy and control the haemorrhage by pressing his finger on the aorta that has just been punctured by the Veress needle.

Major vascular injuries, like this one—frequently fatal—have been reported [2–4].

Those two accidents share the same feature: both are related to a lack of visibility. Los Rodeos tragedy could have been avoided if the KLM captain had seen the aircraft ahead; a major vascular injury could have been avoided if the surgeon had seen the vessel ahead.

In Obstetrics also, lack of visibility explains several major mothers’ or neonates’ injuries.

During centuries, obstetricians have worked under this sort of huge pressure: they worked in a blind environment, and they just had to rely only on their fingertip sensations with no visual access to the neonate’s head or pelvic bone (Fig. 1.1). Ultrasonography use has made invisible visible, and with ultrasound, obstetricians are making a giant leap forward .

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Fig. 1.1

Toucher de femme debout vaginal digital examination in the nineteenth century (from Maygrier GP, Halmagrand. Nouvelles dèmonstrations d’accouchements. Deuxième èd. Paris: Bechet Je et Labè, Libraires de la Facultè de mèdecine de Paris, 1840)

From a safety point of view, it is mandatory to understand that an obstetrician’s main concern is to know whether he should proceed to a specific manoeuvre or cancel it.

Knowing when to avoid or stop a dangerous vaginal delivery or when to avoid or stop an operative vaginal delivery is a key obstetric safety issue.

In 2020, ultrasound enables the obstetrician to:

Visualize the foetal skull and measure the mother vulvar skin to foetal skull distanceviatransperineal route. This will allow avoiding a dangerous operative vaginal delivery if the head is not engaged [5, 6].

Visualize the foetal head positionviatransabdominal route (Fig. 1.2) during the second stage of labour and diagnose a posterior persistent position, which could explain a dystocia and eventually proceed to a rotation or to a caesarean section. Knowing the correct head position will help decrease the rate of asymmetric position of the vacuum device or forceps on the foetal head and help decrease foetal trauma [7–9].

Visualize the foetal head and measure the foetal skull to foetal scalp distance and scan for large caput succedaneumviatransperineal route (Fig. 1.3). This will help to contraindicate a use of a vacuum device on a significant caput succedaneum and will help prevent a life-threatening neonatal subgaleal haematoma [10, 11].

Visualize the cervix and scan its internal osviatransvaginal route (Fig. 1.4), whichallows:

1.

To measure the distance between the placental edge and the internal os, this will help to contraindicate a vaginal delivery when this distance is, at term, less than 2 cm, and this will allow to decrease the per partum haemorrhage risk and indicate a prophylactic caesarean section.

2.

Using the colour Doppler mode to screen for vasa praevia that crosses the internal cervical os; Left undetected, those vessels could lead to catastrophic laceration after membrane rupture during delivery and to a major life-threatening fœtal Benkiser’s haemorrhage leading to a red code cesarean section [12]. Once suspected and confirmed, this will allow the obstetrician to schedule an appropriate caesarean section to prevent the haemorrhage [13, 14].

Visualize the caesarean scar location on the uterus via transabdominal route, which allows:

1.

To check that this region is placenta-free. Each time placenta covers this region, the obstetrician will suspect a placenta accreta and will perform a referent ultrasonography and an MRI of the placenta. This placenta accreta screening method will prevent life-threatening maternal haemorrhage. Obstetrician will be enable to perform either a specific placenta-free hysterotomy followed by a conservative approach or a hysterectomy performed by a surgical twin team consists of an obstetrician surgeon and a urological surgeon [15, 16].

2.

To check for a uterine wall gapon the scar location; such a gap will be responsible for an amniotic sac hernia. Such a discovery will contraindicate a vaginal delivery and allow the obstetrician to schedule a CS that will prevent a possible uterus rupture [17, 18].

Visualize the bladder and check for a full bladderviatransabdominal route:

1.

During labour, a full bladder is frequently associated with a lack of bladder sensitivity secondary to epidural analgesia. Unseen, such a full bladder can create a praevia obstacle and create a dystocia that can lead to an inappropriate operative vaginal delivery or caesarean section.

Once detected, emptying the bladder will cure the dystocia and hence prevent unnecessary caesarean section or unnecessary operative vaginal delivery.

2.

During post-partum, a distended bladder can shut the cervical canal and lead to a major post-partum haemorrhage (PPH) [19]. Emptying the bladder will cure the PPH.

Estimate a foetal weight. This will allow to contraindicate a vaginal delivery when the foetal weight is suspected to be over 5000 grams (or over 4500 gr. should a gestational diabetes be present). In such cases, scheduling a caesarean section will reduce the shoulder dystocia risk, will avoid dangerous operative vaginal delivery, and will avoid severe perineal trauma.

Operative vaginal delivery is a meaningful example of ultrasonography value.

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Fig. 1.2

Transabdominal transversal ultrasonographic scan of foetal head in transverse and asynclitic position in labour

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Fig. 1.3

Translabial ultrasound longitudinal scan with foetal head in occiput posterior position during the second stage of labour

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Fig. 1.4

Transvaginal ultrasonography in early stage of labour

The first step of every operative vaginal delivery (forceps or vacuum device) is the mental visualization of the neonate. This mental visualization should allow the obstetrician to visualize the foetal head including its eyes and nose as well as the foetal back. This mental visualization will help the obstetrician to perform a symmetrical application of the forceps blades or of the vacuum cup on the foetal head. This symmetrical application will enable to develop mechanical forces as low as possible and as symmetrical as possible [6, 10, 20]. This mental visualization will also help to apply the appropriate traction axis during forceps deliveries (Fig. 1.5).

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Fig. 1.5

Ultrasonographic detection of head position in the second labour stage before the Kielland forceps application

Visualization of the foetus may also benefit to the obstetrician. Indeed, blind procedures may increase the obstetrician’s stress and hence decrease his or her abilities. On the contrary, increasing visibility may decrease the obstetrician’s stress and hence sustain his/her professional skills.

One should be careful; indeed, every new technology introduces new pitfalls and new risks.

Here the risk will be to go from a full clinical practice to a full utrasonographical practice.

Obstetricians should of course be aware of and fully trained with the clinical practice and add the ultrasonography practice as a new valuable tool.

Ultrasound use has allowed us to move from the blind twentieth-century obstetrics to an ultrasound twenty-first-century obstetrics. Ultrasonography helps to anticipate hazardous situations and helps obstetricians to choose the less dangerous track for both mothers and foetuses.

This book from our colleague, Professor Antonio Malvasi, is a fantastic journey into the world of obstetricians working worldwide to make unseen visible and hence increase mothers and neonates’ safety.

References

1.

https://​m.​youtube.​com MayDay—Danger dans le ciel Catastrophe de Tenerife.

2.

Guloglu R, et al. Major retroperitoneal vascular injuries during laparoscopic cholecystectomy and appendicectomy. J Laparoendosc Adv Surg Tech A. 2004;14(2):73–6.Crossref

3.

Pickett S, et al. Avoiding major vessel injury during laparoscopic instrument insertion. Obstet Gynecol Clin N Am. 2010;37(3):387–97.Crossref

4.

Asfour V, et al. Vascular injury at laparoscopy: a guide to management. J Obstet Gynaecol. 2018;38(5):598–606.Crossref

5.

Dupuis O, et al. Comparison of instrument-associated and spontaneous obstetric depressed skull fractures in a cohort of 68 neonates. Am J Obstet Gynecol. 2005;192(1):165–70.Crossref

6.

Dupuis O, et al. Birth simulator: reliability of transvaginal assessment of fetal head station as defined by the American College of Obstetricians and Gynecologists Classification. Am J Obstet Gynecol. 2005;192(3):868–74.Crossref

7.

Dupuis O, et al. Fetal head position during the second stage of labor: comparison of digital vaginal examination and ultrasonographic examination. Eur J Obstet Gynecol Reprod Biol. 2005;123(2):193–7.Crossref

8.

Dupuis O. Simulation et extraction instrumentale. La théorie de la symétrie (théorie de l’œuf) In Mises à jour en Gynécologie et Obstétrique Collége National des Gynécologues Obstétriciens Français 2013. Vigot editions Paris Pages 437–443.

9.

Lapeer R, et al. A computer based simulation of obstetric forceps placement. Med Image Comput Comput Assist Interv. 2014;17(pt2):57–64.PubMed

10.

Chadwick LM, et al. Neonatal subgaleal haematoma: associated risk factors, complications and outcome. J Paediatr Child Health. 1996;32(3):228–32.Crossref

11.

Lee SJ, et al. The clinical characteristics and prognosis of subgaleal hemorrhage in newborn. Korean J Pediatr. 2018;61(12):387–91.Crossref

12.

Dupuis O, et al. Red, orange and green caesarean sections: a new communication tool for on-call obstetricians. Eur J Obstet Gynecol Reprod Biol. 2008;140(2):206–11.Crossref

13.

Fung TY, et al. Poor perinatal outcome associated with vasa previa: is it preventable ? A report of three cases and review of the literature. Ultrasound Obstet Gynecol. 1998;12(6):430–3.Crossref

14.

Nelson LH, et al. Diagnosis of vasa praevia with transvaginal and color flow Doppler ultrasound. Obstet Gynecol. 1990;76(3Pt2):506–9.PubMed

15.

Finberg HJ, et al. Placenta accreta: prospective sonographic diagnosis in patients with placenta praevia and prior cesarean section. J Ultrasound Med. 1992;11(7):333–43.Crossref

16.

Warshak CR, et al. Accuracy of ultrasonography and magnetic resonance imaging in the diagnosis of placenta accrete. Obstet Gynecol. 2006;108(3Pt1):573–81.Crossref

17.

Al-Kufaishi A, et al. An unusual cause for epigastric pain in pregnancy. Spontaneous uterine rupture with herniation of the amniotic sac in a 33-week primigravida. BMJ Case Rep. 2014. Published Online; https://​doi.​org/​10.​1136/​bcr-2013-202973.

18.

Woo JY, et al. Silent spontaneous uterine rupture at 36 weeks of gestation. Case Rep Obstet Gynecol. 2015;2015:596826. published online 2015 Aug 19PubMedPubMedCentral

19.

Dupuis O. Post partum haemorrhage and post partum urinary retention: could voiding be the best way of avoiding a post partum haemorrhage ? BJOG. 2011;118(8):1023–4. author reply 1024–5Crossref

20.

Dupuis O, et al. A new obstetric forceps for the training of junior doctors: a comparison of the spatial dispersion of forceps blade trajectories between junior and senior obstétricians. Am J Obstet Gynecol. 2006;194(6):1524–31.Crossref

© Springer Nature Switzerland AG 2021

A. Malvasi (ed.)Intrapartum Ultrasonography for Labor Managementhttps://doi.org/10.1007/978-3-030-57595-3_2

2. Brief History of Intrapartum Ultrasonography

Reuven Achiron¹, ²   and Laura Adamo³  

(1)

Department of Obstetrics and Gynecology, Prenatal Diagnostic Unit, Chaim Sheba Medical Center, Tel-Hashomer, Israel

(2)

Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel

(3)

Department of Obstetrics and Gynecology, IRCCS Fondazione Policlinico San Matteo, University of Pavia, Pavia, Italy

Laura Adamo (Corresponding author)

Email: [e-mail]

2.1 Before Intrapartum Ultrasound (IPU)

The importance of the pelvis, as a relevant factor in the birth process, dates back to the beginning of the eighteenth century. In 1701, the Dutch obstetrician and orthopedic Hendrik van Deventer (Fig. 2.1) published a handbook for midwives, in which he described with precision the pelvis. He distinguished between three types of pelvis responsible for difficult births: too wide, too small, and too narrow [1].

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Fig. 2.1

Hendrik van Deventer (1651–1724)

Few years later, William Smellie (Fig. 2.2a) started to study the pelvis deformities. He suggested that absolute measurements of pelvic size might help to distinguish between normal and pathological pelvis, introducing the digital transvaginal measurement of the diagonal conjugate (Fig. 2.2b).

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Fig. 2.2

(a) William Smellie (1697–1763). (b) Digital transvaginal measurement of the diagonal conjugate

He noted that the critical diameter of the pelvis was the transverse diameter of the brim, and that in small pelvis, like in the women with rickets, the difficulties of birth were at this level [2, 3] (Fig. 2.3).

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Fig. 2.3

Smellie identified the transverse diameter of the brim as a critical level in women with small pelvis

After Smellie’s observations, the transverse diameter of the pelvis was recognized as a critical factor in the mechanism of birth. The identification of an abnormal pelvis became mandatory to prevent obstructed labors.

In 1803, Franz Karl Naegele (Fig. 2.4a), professor of midwifery in Heidelberg, described the first congenital abnormal pelvis, the obliquely contracted pelvis (Fig. 2.4b). Until then, deformity of the pelvis in the absence of local disease had been attributed only to rickets, osteomalacia, or tuberculosis [4] (Fig. 2.4c).

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Fig. 2.4

(a) Franz Karl Naegele (1788–1851). (b) The obliquely contracted pelvis. (c) The Naegele asynclitism (or anterior asynclitism of the pelvis)

The concept of malproportion, as the discordance between the fetal head and the pelvis size, was now clear, and the studies of the nineteenth century were focused on how to deal with obstructed labors.

Gustav Adolf Michaelis dedicated most of his studies measuring the normal, narrow, and deformed pelvis, not only on corpses and skeletons but also on living women. He stressed the importance of precise and appropriate measurements, demonstrating the inaccuracy of the external pelvimetry. He validates what Smellie proposed a century before: the diagonal conjugate as a reflection of the inner dimension of the pelvis, the conjugate vera [5].

In addition to the pelvimetry, Michaelis correlated the internal pelvic dimension with the external surface of the sacrum, describing the rhomboid that until today is known as Michaelis Rhomboid [6] (Fig. 2.5).

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Fig. 2.5

Gustav Adolf Michaelis (1798–1848) described the external surface of the sacrum, the Michaelis’ Rhomboid, as a useful anatomic landmark to identify contracted pelvis

With the increasing attention on the pelvis and with the growing recourse to induction of labor, the concerns of obstetricians in the first decades of the twentieth century changed. The real challenge was no longer to determine the normal from the abnormal pelvis but the identification of the potential abnormality and the characterization of borderline cases.

In 1896, Roentgen’s announced the discovery that transformed the idea of pelvimetry: the X-ray technology (Fig. 2.6).

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Fig. 2.6

Radiographic image of the upper strait (obtained with Thomas’s roentgen-pelvis graphic technique) of a gynecoid pelvis according to the classification of Caldwell and Moloy

Major improvements in pelvimetric methods took place since the introduction of X-ray, and in 1933, Caldwell and Moloy, from Columbia University, created the well-known classification of pelvic shapes, dividing the pelvis into gynecoid, anthropoid, android, and platypelloid [7].

Again, the trend changed, and more emphasis was given to the dynamic mechanism of the labor, in which the combination of factors, such as pelvic shape and size, fetal head size and moldability, and the force of labor, can determine the outcome of the delivery.

Soon afterward a tool, originally developed for military purposes, radically reformed the medical world. The article that established the beginning of ultrasound in obstetrics and gynecology was published by Ian Donald in 1958 (Fig. 2.7a, b). In his report Investigation of abdominal masses by pulsed ultrasound, he showed for the first time ultrasonographic pictures of the fetal head, twins, polyhydramnios, early pregnancy, fibroids, and ovarian cysts [8].

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Fig. 2.7

(a) Ian Donald (1910–1987). (b) Ultrasonographic pictures of the fetal head in the late 1950s

When, in the early 1960s, obstetricians began to explore the possibilities of replacing X-ray with ultrasound technology, the attention shifted from the mother’s pelvis to the fetus. The desire to understand the process of fetal development grew exponentially.

The first anomalies diagnosed thanks to the ultrasound were a case of anencephaly in 1964 and a case of polycystic kidneys in 1970 [9, 10]. However, the ultrasound prenatal diagnosis began when Campbell and his group reported the diagnosis of anencephaly at 17 weeks followed by an elective termination of pregnancy [11].

The inadequate fetal growth was a major issue, and the identification of abnormally small or abnormally big fetuses became essential in order to plan interventions and prevent complications.

Because images of the head were the most easily recognizable part of the fetal anatomy, it was the first measurement taken in the fetus. Throughout the later 1960s and the 1970s, the technique of biparietal diameter measurement became widely used. The first cephalometry graph from 13 to 40 weeks was used to identify fetuses with a slower growth rate of the biparietal diameter in the third trimester [12].

In 1975, Campbell identified the value of the abdominal circumference measurements in estimating fetal weight and the possible tool to identify intrauterine growth restriction [13], while O’Brien et al. in 1981 were the first to introduce the concept of using limb length, in their case the femur, to predict gestational age [14].

In 1980, Frank Manning and Larry Platt introduced the concept of fetal biophysical profile test which included an assessment of breathing movements, motor activity, amniotic fluid, fetal tone and a cardiotocography analysis for 30 min [15]. The advent of color Doppler made the visualization of fetal vessels much easier, and the first vessels studied to evaluate fetal well-being were the umbilical artery and middle cerebral artery in the early 90s. In 1991, Kiserud described the measurement of the pulsatility of the ductus venosus as a sign of cardiac function and indicator of fetal asphyxia [16].

Several studies in the early 1980s using transabdominal sonography drew attention to the association between a short cervix, funneling with cervical incompetence, and preterm birth. With the introduction of high-frequency transvaginal probes, Frank Andersen provided a risk for preterm delivery based on a cervical length [17].

Of course, the ultrasound changed also the outcome of the pregnancies complicated by placenta previa. The first article about placenta previa was published by Mitzuno et al. in 1965, but only after the introduction of the transvaginal probe, the location of the placenta became feasible and accurate also for posterior placentas.

These studies are just some of the milestones that allowed the development of the ultrasound in the obstetric clinical practice as we know it today.

Ultrasound became so popular because it was cheaper, feasible, reproductible, harmless, and can be used as a screening in all women.

Despite the incredible steps forward in the study of the fetus, the labor remained exclusively confined to the digital assessment.

2.2 The Birth of IPU

A dystocic labor is the result of a disparity between the capacity of the maternal pelvis and the fetal head due to bony architecture, soft tissue or cervical resistance, fetal malpositioning, or a combination of these conditions. Obstructed labor remains an important cause of maternal death as well as neonate’s short- and long-term disability [18].

Before ultrasound, imaging of dystocic labor has been obtained by X-ray and magnetic resonance imaging (MRI). These two methods gave a major contribution in describing and understanding the mechanism of the fetal descendent. However, X-ray pelvimetry had the disadvantage of ionizing radiation exposure, and it did not offer diagnostic accuracy in predicting dystocia. MRI, which does not involve radiation, made it possible to assess the relationship between pelvic diameter and fetal head dimensions. It allowed to estimate pelvic capacity [19], but none of the MRI parameters measured were significantly helpful in obstructed labor [20]. The assessment of the pelvis dimensions kept being predominantly manual, reserving the imaging only for high-risk cases.

The first group that described the feasibility on determining the obstetric conjugate by ultrasound was Katanozaka et al. in 1999 [21].

They identified, by a transabdominal approach, the superior margin of the pubic bone and the sacral promontorium in 209 women at 28 weeks and at 36 weeks (Fig. 2.8). The ultrasonic obstetric conjugate lengths ranged from 10.7 to 15.1 cm, and comparing the ultrasound results with the radiographic obstetric conjugate, they found a positive correlation. In the 26 cases where a cesarean section was performed, 50% of these had an obstetric conjugate length shorter than 12 cm.

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Fig. 2.8

Katanozaka demonstrates a positive correlation between the transabdominal ultrasonic obstetric conjugate and the radiographic obstetric conjugate

This was the first study that used ultrasound to evaluate pelvis dimensions during the pregnancy, demonstrating how ultrasound could play an important role in identifying high-risk patients for cephalopelvic disproportion.

Although this paper was the first one that correlated ultrasound and pelvimetry, the study that marked the birth of the ultrasound in the delivery room was published in 1989 by William Rayburn, at that time a senior resident in University of Nebraska [22].

He proposed to determine the position of fetal occiput by transabdominal ultrasound to improve the accuracy of the traditional method. Analyzing 83 women with arrest of the second stage, he showed that only in the occiput transfer position the clinical impression was reliable enough without ultrasound, while in the occiput anterior and occiput posterior position, ultrasound gave a major support to the digital assessment, especially in presence of caput succedaneum or molding. Rayburn pointed out how a more accurate position of the fetal head could have helped the decision of performing a cesarean or an operative delivery, preventing the adverse outcomes of a prolonged labor.

This study introduced the abdominal ultrasound in the delivery room, but only to confirm or rectify digital findings: the transvaginal examination was the gold standard, but its accuracy was never analyzed scientifically (Fig. 2.12a, b).

In 2001, Kreiser et al. [23] resumed Reyburn’s concept, this time questioning the reliability of the vaginal examination (Fig. 2.9a). They compared the digital and the ultrasound findings in determining the head position in low-risk women during the second stage of labor. Right after the traditional vaginal examination, the head position was determined using both transabdominal and transperineal ultrasound, identifying the fetal spine, the fetal eyes, and the intracranial midline. The occiput position assessed digitally, even by experienced obstetricians, was wrong in 30% of the cases, while the ultrasound findings were incorrect only in 7% of the cases. This study showed for the first time the superiority of the ultrasound upon an intrapartum digital evaluation and was the first paper where the new transperineal approach was applied (Fig. 2.9b).

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Fig. 2.9

(a and b) Kreiser demonstrates the superiority of ultrasound in assessing occiput position during the second stage of labor

A year later, also David Sherer (Fig. 2.10a) focused the detection of fetal head position with the digital and the sonographic techniques. He conducted two studies, one was performed during the active stage and one during the second stage of labor (Fig. 2.10b, upper and down).

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Fig. 2.10

(a and b, upper, down) David Sherer demonstrates the unreliability of the vaginal examination in determining the fetal head position during active labor and the second stage

In the first work, transvaginal digital examinations agreed with ultrasound assessments for only 24% of the patients [24]. In the second stage of labor, the results were not more reassuring: clinical and ultrasound examinations agreed only on 35% of the findings [25]. The error rate of the digital transvaginal examination was 76% during active labor and 65% during the second stage. After Sherer, several studies demonstrated the inferiority of the vaginal exploration in determining the head position [26, 27].

After the head position, the potentiality of the ultrasound in the delivery room shifted to another great challenge: the head station. Studies started to show how digital estimation of the fetal head descent in the birth canal was imprecise and poorly reproducible.

Dupuis et al. in 2005 investigated the accuracy of transvaginal assessment of fetal head station using a birth simulator with predefined stations.

He tested 57 physicians of the American College of Obstetrics and Gynecology, both residents and senior doctors, on the reliability of their clinical assessments of engagement and fetal station [28]. The digital estimations were incorrect in 50–88% of cases for residents and in 36–80% of cases for the seniors.

Moreover, when the stations were divided in high-, mid-, low-pelvis and outlet, a high-pelvic station was erroneously diagnosed as a mid-pelvis in 88% of the residents and 67% of the obstetricians. These results were alarming since a misdiagnosis at every station can have serious implications in labor management. Additionally, the birth simulator did not include the phenomenon of molding or caput succedaneum; thus, the error rate was likely to be even higher in a delivery room.

It was clear how a more objective method to assess the head level was needed.

The first proposal arrived from Dietz and Lanzarone in 2005 [29]. They suggested a sagittal transperineal ultrasound approach to assess the fetal head descent with a measure that they called Progression Distance (Fig. 2.11a).

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Fig. 2.11

(a and b) Dietz and Lanzarone in 2005 proposed the Progression Distance

One hundred and thirty-nine women in the first stage of labor were evaluated to determine the fetal head station measuring the minimal distance between the leading edge of the fetal skull and a line positioned at a 90° angle from the central axis of the pubic symphysis (infrapubic line) in the midsagittal plane (Fig. 2.11b).

Their method showed a reasonable correlation between the sonographic and clinical evaluation of the fetal station. However, in clinical practice, the critical level for the determination of the head is when the ischial spines are not digitally detectable anymore, and this study considered only the first stage of labor.

A year later, Henrich et al. [30] (Fig. 2.12a) described another transperineal sonographic parameter to demonstrate the head engagement and station determining the deflection and the direction of the fetal head.

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Fig. 2.12

(a and b) William Henrich and the Head Direction

They also used the infrapubic line as a reference, and they calculated the angle with a line perpendicular to the widest diameter of the fetal head (Fig. 2.12b). Following this technique, they determined three types of head direction: head down, head horizontal, and head up.

Considering the path that the fetal head follows in the birth canal, they observed that at high stations, the fetal head pointed downward, while at low stations, the head pointed upwards. They applied this method in 20 women at the second stage of labor with indication for operative delivery, and they found that an upward direction of the fetal head was a good prognostic value for a successful operative vaginal delivery, contrary a downward or horizontal direction was associated with a difficult extraction.

Eggebo et al. (Fig. 2.13a), in the same year, proposed another TPU measurement to define the engagement of the fetal head: the head–perineum distance (HPD) (Fig. 2.13b). In a transverse view, they measured the shortest distance from the outer bony limit of the fetal skull to the skin surface of the perineum.

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Fig. 2.13

(a and b) Torbjorn Eggebo and the Head-Perineum Distance

They conducted two studies to assess the benefit of this new method. In the first, they demonstrated that a short HPD (<45 mm) in women with PROM gave a high probability of a rapid and uncomplicated labor [31], while, in the second study, they found that the clinical value of the HPD was similar to the ultrasound-measured cervical length and the Bishop score in predicting vaginal delivery after induction [32]. Compared to the methods suggested before, the advantage of the HPD is that it can be obtained at all stations and for all positions of the fetal head.

In 2009, Ghi et al. (Fig. 2.14a) suggested to determine the progression of the fetal head using the transperineal midline angle (MA) [33]. After the digital assessment of the head station, they measured the angle formed by the fetal intracranial midline and the anteroposterior diameter of the pubis and divided into two groups: ≥45° and <45° (Fig. 2.14b). Among the 140 ultrasound examinations of the midline, a rotation of ≥45° was found with a station ≤+2 cm, whereas rotation of <45° was observed for stations ≥+3 cm.

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Fig. 2.14

(a and b) Tullio Ghi and the Midline Angle

The MA not only showed a high correlation with the digital examination, but it also helped to predict the success of operative vaginal delivery: in fetuses with occiput anterior and a MA less than 45°, none of the vacuum extractions failed.

Moreover, in 2009, Barbera et al. [34] (Fig. 2.15a) pointed out that previous sonographic techniques to assess the fetal head stations did not consider the curved shape of the pelvis. The fetus in fact has to pass through an ark-like pathway to move from the upper to the lower portions of the pelvic canal.

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Fig. 2.15

(a and b) Antonino Barbera and the Angle of Progression

His group proposed the idea of angle of progression (AoP) as the angle between a line through the midline of the pubic symphysis and a line from the inferior apex of the symphysis to the leading part of the fetal skull (Fig. 2.15b). They observed a progressive increasing of this angle with fetal head descent, and they noticed that an angle wider than 120° was associated with spontaneous delivery. In support of this last observation, all the women in the study that underwent cesarean section because of prolonged second stage had an AoP below 108°.

In the same year, Kalache et al. [35] analyzed the AoP in women with prolonged second stage. They found that with an AoP of 120°, the probability of an easy vacuum extraction or a spontaneous vaginal delivery was 90%.

This measurement became rapidly popular because, relatively to the different techniques to determine the fetal head station, the AoP was the easiest to obtain, the easiest to teach, and the fastest to use [36].

To analyze the relationship between the AoP and the concept of head level, Bamberg et al. in 2011 conducted a validation study using an open MRI [37].

First, the head station was assessed on MRI images measuring the distance between the fetal head and the interspinal plane, afterwards the AoP was measured by transperineal ultrasound. They found a significant correlation between the two parameters, and they calculated that the 0-station corresponded to an AoP of 120°.

A year after, the same group calculated the AoP on open MRI images and compared it with the same measurement obtained with the transperineal technique. They found a significant agreement between the angle wideness obtained with the two methods: a mean angle of 79.05° by ultrasound and a mean angle of 80.48° by MRI [38].

In 2013, Youssef et al. [39] (Fig. 2.16a) calculated the distance between the lower edge of maternal symphysis pubis and the fetal skull, along the infrapubic line, suggesting the head–symphysis distance (HSD) (Fig. 2.16b) as a simple linear measurement able to tolerate even significant displacement of the transducer from the midsagittal plane of the pelvis.

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Fig. 2.16

(a and b) Aly Youssef and the Head-Symphysis Distance

They showed how this distance became shorter with the progressive descent of the fetal head through the lower portion of the pelvis. HSD was negatively correlated to fetal head station and AoP.

In 2013, also Gilboa et al. [40] (Fig. 2.17a) used the intrapartum US to help the management of obstructed labor, but they did not focus their attention on how the fetus interacts with the maternal pelvis. They objectively demonstrated how the pelvis outlet plays a critical role in prolonged second-stage labors.

../images/301474_2_En_2_Chapter/301474_2_En_2_Fig17_HTML.jpg

Fig. 2.17

(a and b) Yinon Gilboa and the Pubic Arch Angle

Using a transperineal ultrasound image that showed the pubic symphysis and the two symmetrical inferior pubic rami, Gilboa measured the angle between the inferior borders of the pubic rami that converge at the middle of the pubic symphysis (Fig. 2.17b).

They found that the mean pubic arch angle (PAA) was 101.1° and that the degree of PAA correlated with the type of delivery: spontaneous vaginal delivery had a wider PAA compared to operative vaginal delivery. Moreover, none of the women with a PAA <90° delivered spontaneously, and all the women with fetuses in occiput transverse positions had a smaller PAA.

The PAA reflects the dimension of the pelvic outlet, and a narrow pelvic outlet is often associated with midpelvic contraction. The group used this parameter during prolonged second-stage labors, but the PAA can add important information even before the onset of the labor, especially in women where cephalopelvic disproportion is suspected.

These studies are the foundations from which IPU started to be considered as a need and not a luxury.

This concept has been brought to its maximum potential by Hassan et al. (Fig. 2.18a), in 2014, when they replaced the classic digital assessment in labors with a partogram based only on US findings. They created the sonopartogram [41] (Fig. 2.18b).

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Fig. 2.18

(a and b) Wassim Hassan created the Sonopartogram, a partogram based only on ultrasound findings

They assessed the cervical dilatation transperineally, the head position transabdominally, and the head station measuring the HPD. Among 20 women, they successfully fulfilled 95% of the sonopartograms and 82% of the traditional partogram. The agreement between the digital and US evaluation of the cervical dilatation was satisfying; however, US was not able to determine cervical dilatation beyond 9 cm. The fetal head position could not be assessed digitally in 54% against the 2% of the ultrasound. The head station could be successfully measured in all cases with both methods.

Even if neither the techniques were perfect, the aim of this work was to show the importance and the enormous clinical potential IPU.

2.3 Current Trend

The papers illustrated before are the milestones of a flourishing literature, which will be addressed in detail within the next chapters.

As demonstrated, the use of IPU is relatively recent, and its acceptability between midwifes and obstetricians is not ubiquitous yet. As advancements in IPU progress, a concern arises with the idea of losing the art of Obstetrics as overreliance on technology develops.

A study conducted in Israel in 2017 by Reuven Achiron and his group (Fig. 2.19a) showed how the ultrasound in the delivery room is mostly used for fetal presentation, placental location, or in twin deliveries. Its advanced use is still overtaken by the clinical experience both for seniors and interns, even though the limitations of digital examination has been widely demonstrated [42] (Fig. 2.19b).

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Fig. 2.19

(a and b) Reuven Achiron shows how obstetricians still prefer digital examination, despite the demonstrated advantages of the ultrasound

Any method proposed for practical use in the delivery room must be reliable, easy to understand and to perform, and must be acceptable for both patients and their caregivers [43]. If we compare the digital examination with the sonographic evaluation, ultrasound demonstrated to be superior in all these aspects.

The vaginal examination is subjective and depends mostly on the examiner’s experience and labor conditions. It is even more inaccurate in the case of caput succedaneum, molding, or malpositions, and the agreement between assessors is frequently poor [28, 44].

Studies demonstrated that head position is imprecise in a third of vaginal examinations prior to instrumental delivery [26, 34, 45]. Clinicians agree on cervical dilatation in only approximately 50% of cases [46], and similarly fetal head station is poorly reliable [28]. An erroneous assessment of the progression of the labor can increase the risk of inappropriate management.

Furthermore, vaginal examination is associated with ascending infection to the fetus, chorioamnionitis, and endometritis as well as reduced time to delivery in preterm labor [47]. Moreover, digital examination is intrusive, uncomfortable, and can become a real trauma for women with a previous sexual trauma or vaginismus.

Hence, there is a clear rational for the development of a less unpleasant and more reproducible technique to assess the labor.

IPU has been demonstrated to perform better than clinical examinations in the assessment of the fetal head station [28, 33, 34, 39, 43] head position [26, 45, 48] and in the diagnosis of the malpositions and malpresentations of the fetal head [49–51].

It is not time-consuming and is well accepted by women. In a recent research by Rizzo et al. [52], ultrasound examination scored significantly higher than vaginal examination in intrusiveness and privacy ensured. Several studies reported also a lower pain score with the ultrasonographic assessment [53–55].

Ultrasound measurements are highly reproduceable and are much easier to learn compared to the vaginal examination, even for caregivers without any previous experience in the delivery room, like student midwifes [56]. For senior obstetricians, theoretical and practical courses conducted by experts might change obstetrician’s perspective on the use of ultrasound in the labor ward, as recently demonstrated by Youssef et al. [57].

Another positive aspect recently investigated is the patient’s psychological benefit in being able to follow on the ultrasound monitor how the fetal head descent and position are being assessed. This effect is the result of the visual biofeedback.

Pilot studies conducted to evaluate the effect of the visualization of the progression of the delivery, showed that women with visual biofeedback were able to improve the pushing efficacy. The duration of the active phase of second stage was reduced by 33% with a decrease perineum lacerations and an increased the sense of connection of the mother with the newborn [58, 59].

Furthermore, ultrasonography is an objective documentation of the labor that can be stored in the patient’s records, which is important in reducing diagnostic errors and complications, but it can also be essential from a legal point of view. Ultrasound measurements can be used as proofs to explain the decision-making process about a complicated delivery and the consequential managing of adverse events, giving evidence of professional correctness in case of suing [60].

The advantages of IPU are clear and demonstrated, but what is the role of this technique in the daily clinical practice?

In 2018, The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) published first practice guidelines for IPU [61], reviewing the literature and clarifying the parameters and their concrete application.

ISUOG stated the following indications for the ultrasound evaluation of the labor:

Slow progress or arrest of labor in the first stage: HPD and AoP are more accurate than digital examination in predicting vaginal delivery in nulliparous women with prolonged first stage of labor (Level of Evidence: 2+, Grade of Recommendation: B) [62, 63].

Slow progress or arrest of labor in the second stage: a favorable head direction (head up) is associated with spontaneous vaginal delivery in 80% of the cases (Level of Evidence: 2+, Grade of Recommendation: B) [64].

Ascertainment of fetal head position and station before considering or performing instrumental vaginal delivery: The combined use of ultrasound and digital examination to detect the fetal head position prior to instrumental vaginal delivery is significantly more accurate compared with digital examination alone (Level of Evidence: 1–, Grade of Recommendation: A) [45].

Wong et al. [48] demonstrated that when the fetal head position is determined by ultrasound, the placement of the suction cup is significantly closer to the flexion point (Level of Evidence: 1–, Grade of Recommendation: A).

AoP is a predictor of successful vacuum delivery in fetuses in occiput anterior position. A cut-off value of 120° was found to predict an easy and successful vacuum extraction in 90% of cases (Level of Evidence: 2+, Grade of Recommendation: B) [35].

Ultrasound can help to predict the outcome of forceps delivery in occiput anterior position: an AoP < 138° and a PD <4.8 cm are strong predictors of complicated procedures (Level of Evidence: 2+, Grade of Recommendation: B) [65].

AoP can help to predict the chance of a successful or unsuccessful vacuum extraction: failed vacuum delivery is associated with a significantly smaller median AoP (136.6° vs 145.9°) (Level of Evidence: 2+, Grade of Recommendation: B) [66].

Objective assessment of fetal head malpresentation: the use of ultrasound to support the clinical diagnosis of malpositions and malpresentations has been reported recently (Level of Evidence: 3, Grade of Recommendation: C) [67–70].

Antonio Malvasi (Fig. 2.20a) has studied asynclitism using the transabdominal and translabial technique [70], describing ultrasound signs which can assist a more accurate diagnosis compared to vaginal digital examination. The most simple asynclitism sign is the Squint Sign (or single orbit sign, or Malvasi sign) (Fig. 2.20b).

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Fig. 2.20

(a and b) Antonio Malvasi demonstrates how ultrasound can detect malposition and asynclitism of the fetal head with the Squint Sign (or single orbit sign, or Malvasi sign)

The guidelines summary those indications in the following recommendations [61]:

(a)

Suspected delay or arrest of first or second stage. We recommend measurement of either AoP or HPD transperineally and assessment of head position transabdominally.

(b)

Potential need for performance of operative vaginal delivery. We recommend assessment of head position by transabdominal ultrasound and suggest measurement of fetal head station by transperineal ultrasound. The most reliable sonographic parameters to predict outcome of the procedure are HPD and AoP. MLA and/or head direction may also be useful to further predict the likelihood of a successful extraction.

The ideal ultrasound method should be easy to perform, easy to learn, clinically valuable, useful at all stations, useful for all positions, applicable to all women, acceptable to women, have high repeatability, and be operator-independent [71].

To find this ideal method, we need first to overcome some limitations [72]:

Most of the hospitals do not have an ultrasound machine permanently available in the delivery rooms.

Most of the studies conducted until now considered small size populations, are non-randomized, and lack stratification of the data according to parity, ethnicity, maternal age. The relationship between IPU and analgesia, preterm, and inducted labors need to be deeply explored. Collecting more data will allow us to assess if IPU can significantly lower the cesarean rate and improve fetal outcomes.

Not all obstetricians have sonographic skills and not all of the parameters described before are easy to obtain without a training and practice; this may scare the physicians and interfere with the use of ultrasound during labor in clinical practice.

IPU should not replace clinical examinations but can be used as a complementary tool. Certainly, labor is a complex process that requires interaction of many factors, ultrasound should supplement and not undermine the clinician’s skills.

Professor Giancarlo Di Renzo (Fig. 2.21) has carried out in the last decades an intense national and international educational activity, promoting the introduction of new technologies in fetal maternal medicine and promoting the concept and study of periconceptional medicine, this however not distinct from a clinical and semiotic traditional education and from the personalized approach of care for the mother and the fetus. He is the founder and Director of the renowned PREIS School of Firenze, dedicated to improving professional achievements in the field of maternal infant care.

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Fig. 2.21

Giancarlo Di Renzo

2.4 Future Perspectives

Every pregnant woman at term that arrives at the hospital wishes to know if she will be able to deliver vaginally, or if she will require a cesarean section. Meanwhile, on the other side of the desk, the doctor has the same concern.

Authors started to combine the intrapartum ultrasound with maternal parameters to predict the chance of a successful vaginal birth, especially during a prolonged second stage [73].

Furthermore, the combination of intrapartum determinations and new advanced technologies is being tested.

The laborPro magnetic position-tracking system is the only automated system used to assess the labor that has been approved from Food and Drugs Administration and European CE conformity. The laborPro can: determine automatically the fetal head position and station assessed by ultrasound, it can measure the cervical dilatation and the pelvic diameters with a ruler like system, it can monitor vacuum and forceps extraction with a 3D real-time reconstruction and can record the entire labor procedure [74, 75]. This technology has been used as a noninvasive method to predict obstructed labor in low-risk patients [76], but despite the potential capability to assess abnormal labor, the clinical benefits should be evaluated by larger studies.

A recent pilot study tested a smartphone application to stratify the change of vaginal delivery. Ultrasonographic measures and maternal characteristics (digital cervical dilatation, sonographic head position, head–perineum distance, maternal age, body mass index, and presence or absence of prolonged labor) were recorded in the app that gives, as output, a high, medium, or low likelihood of vaginal delivery. They used the app on 190 women, and the length of the labor was significantly longer with the decreasing likelihood percentage: 721 min in the high likelihood group versus 1239 min in the low likelihood group [77].

Prediction of a prolonged second-stage labor could decrease several maternal and perinatal complications, including operative vaginal delivery, cesarean section, severe perineal damage, postpartum hemorrhage, and chorioamnionitis.

However, more attention should be focused on identifying high-risk patients even before the onset of the partum.

When the woman arrives in the labor ward to fill out her medical record, a lot of questions regarding her pregnancy are not relevant in predicting the chance of delivering without complications. The serologic state of Cytomegalovirus or the first trimester risk of aneuploids cannot indicate if the labor will be physiologic.

However, check-in ultrasound could be extremely useful to detect in advance women with higher probability of labor complications.

Some of the sonographic parameters that could be part of this pre-labor assessment are already part of the routine evaluation of a fetus at term: fetal viability and heart rate, presentation of the fetus, umbilical artery flow, amniotic fluid, presence of placenta previa or vasa previa [61].

The role of the mid-cerebral artery flow at term is still controversial, but a fetus with a mild cerebral vasodilatation can indicate a relative hypoxic state, and it might not have enough reserves to endure a long labor.

Because a prolonged second stage can be the result of cephalopelvic disproportion, the size of the fetus and the size of the pelvis should be assessed before the onset of labor.

Head dimensions, among all fetal biometric measurements, have the most relevant role in the progress and outcome of the labor, hence biparietal diameter and head circumference should be part of the ultrasound check-in [78].

PAA is the transperineal ultrasound measurement that reflects the pelvis dimension. It not only represents directly the pelvis outlet, but a recent study demonstrates the positive correlation between PAA and the two other significant components of the birth canal: the interspinous diameter and the obstetric conjugate [79].

Check-in ultrasound and maternal characteristics (Table 2.1) should be part of an algorithm that would be ideally applied to all women during the last weeks of the pregnancy. The results will allocate the patient in an initial risk category. Once labor begins, intrapartum ultrasound findings will modify the initial risk, allowing the physician a better management of the different stages of labor.

Table 2.1

Suggested factors to determine a pre-labor risk of complicated vaginal delivery

All medicine is aspiring toward a personalized approach, and so should obstetrics.

The pre-labor risk could give to a low-risk patient with favorable intrapartum condition a longer time of active pushing. On the other side, a promptly operative delivery will prevent severe complications [80–82] in high-risk patients (with non-reassuring intrapartum findings).

An ultrasound evaluation of labor and delivery improves maternal and neonatal outcome and reduces medico-legal problems and therefore litigation and claims [83–86].

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