Shoulder Dystocia and Birth Injury: Prevention and Treatment

By James A. O'Leary

During the past several years, there has been an extensive reappraisal of the physiologic changes of pregnancy and their associated disorders, along with a refinement of diagnostic procedures and evaluation of the therapeutic approaches that are of primary concern to the physician. In Shoulder Dystocia and Birth Injury: Prevention and Treatment, Third Edition, noted authority James A. O’Leary, M.D., with 40 years experience as an M.D. academician, lecturer, practitioner and clinical researcher with almost 200 contributions to the OB-GYN literature and textbooks, shares his insight on treatment techniques, identification and treatment of predisposing risk factors, current statistical data, ultrasound diagnosis and the necessary steps toward prevention, along with a thorough review of the important medical-legal issues.

Shoulder Dystocia and Birth Injury: Prevention and Treatment, Third Edition supplements the limits of personal experience with the accumulated experience of many talented clinicians to aid physicians, midwives, and professionals in training with the most current information in this vital field.

• Language: English
• Publisher: Humana Press
• Release date: Apr 5, 2009
• ISBN: 9781597454735

Book preview

Part 1

Prevention

James A. O'Leary (ed.)Shoulder Dystocia and Birth Injury3Prevention and Treatment10.1007/978-1-59745-473-5_1© Humana Press, a part of Springer Science+Business Media, LLC 2009

1. Preconceptual Risk Factors

James A. O’Leary¹ 

(1)

Professor Obstetrics & Gynecology (retired), University of south Florida, Tampa, Florida, USA

1.1 Introduction

1.2 Maternal Birthweight

1.3 Maternal Age

1.4 Maternal Height

1.5 Obesity

1.6 Obesity and Diabetes

1.7 Conclusion

References

Summary

Identification of risk factors and anticipation of shoulder dystocia will help prevent fetal injury.

Keywords

diabetesmacrosomiaobesity

1.1 Introduction

The simplest and easiest approach to shoulder dystocia is prevention. Thus, obstetricians must have a high level of anticipatory knowledge to avoid this catastrophic event. Such a mindset can only be developed by learning and identifying those risk factors involved in shoulder dystocia. Identification of critical risk factors will lead to anticipation, which in turn will lead to prevention. The risk factors for shoulder dystocia can be divided into preconceptual risk factors, antepartum risk factors, and intrapartum risk factors. This chapter will deal with preconceptual issues.

Risk factors for shoulder dystocia are similar to those for cephalopelvic disproportion [1–14] and can be considered under the triad of the Three P’s: passenger, passage, and power. Preconceptual, or prepregnancy, risk factors relate only to the passage and the patient herself and should be evident to the examiner at the first office visit. Individuals providing obstetric care should have a firm commitment to the recognition of these risk factors and the knowledge and skill to perform clinical pelvimetry. The preconceptual risk factors are an abnormal pelvis, especially the flat or platypelloid pelvis, and those maternal issues that lead to macrosomia.

A strong index of suspicion for a difficult delivery and birth injury is an ongoing responsibility for providers of obstetric care. The optimum time to identify these risk factors is at the first prenatal visit or first gynecologic office visit. Ideally, a woman receiving preconceptual counseling can be alerted to those factors that might be correctable. For example, maternal glucose intolerance will account for 10% of macrosomic infants. Large maternal stature or excessive weight gain in pregnancy will account for slightly more than 50% of macrosomic infants. Thus, women at risk for glucose intolerance or excessive weight gain can be counseled on the need to monitor such events. However, the cause in at least one third of macrosomic infants remains unexplained [15–21].

1.2 Maternal Birthweight

The value of ascertaining maternal birthweight has recently been reconfirmed [22–31]. Klebanoff et al. [22] demonstrated that a mother’s birthweight has a strong influence on her child’s birthweight. Identifying infants whose macrosomia is due to familial factors is important [23], as this explains some previously idiopathic large infants. It may also make it possible to distinguish those infants with benign macrosomia from the subset of infants that are high risk or large for gestational age (LGA). Furthermore, it alerts the obstetrician caring for the small woman who was herself large at birth to the increased possibility of a large infant at delivery. Klebanoff’s study was one of the first to examine the effect of a mother’s birthweight on her risk of producing a macrosomic infant independent of other known risk factors. It demonstrated that women who were large at birth are at increased risk of giving birth to a large infant. In fact, maternal birthweight is more strongly associated with accelerated fetal growth than is either current maternal height or weight.

This relationship between a mother’s own birthweight and the risk of delivering an LGA infant was based on studies in 1,335 women. Compared with women who weighed 8 lb or more at birth, women who weighed 6 to 7.9 lb were only 50% as likely (P = .007), and women who weighed 4 to 5.9 lb were only 15% as likely (P = .002), to give birth to an LGA infant. When this relationship was adjusted for nine other factors known to influence birthweight, including maternal weight and weight gain during pregnancy, maternal birthweight was second only to weight gain during pregnancy in predicting the birth of LGA infants. Maternal birthweight was also accurate in the prediction of macrosomia (birthweight >4,000 g). Therefore, a mother’s birthweight should become part of the routine obstetric and gynecologic history.

The risk of macrosomia will increase from 15.1% to 31.5% when more than one risk factor is present. Preconceptual counseling will help to identify eight key potential predictors of a shoulder dystocia (Table 1.1). The more factors present, the greater the risk. As suggested, the presence of these factors is not only additive but also may be synergistic.

Table 1.1

Key Preconceptual Historical Risk Factors

1.3 Maternal Age

Since 1980, a rather impressive proportion of American women above the age of 35 years began to have babies, and many of these women were pregnant for the first time [19]. In 1950 was coined the hapless term elderly primigravida as a descriptor of obstetric risk. Five decades later, older maternal age is increasingly an issue of perinatal concern. Live births to women aged 30 to 34 years increased from 18.9% of all live births in 1982 to 30.6% in 2002. The relative change in live births to women 35 years or older was even larger, with the proportion of live births to women 35 to 39 years of age increasing from 4.7% in 1982 to 14.1% in 2002 and those among women 40 years of age or older increasing from 0.6% to 2.6%. Similar increases in older maternal age categories have been observed in other industrialized countries [16].

As a net result of these factors, a larger percentage of American women are between the ages of 35 and 50 years. Combined with the trend among many women to delay childbearing due to women’s career opportunities, advanced education, infertility, control over fertility, late and second marriages, and financial concerns, the birth rate for the 1990s has shown a dramatic increase for women older than 35 years. The United States Bureau of the Census estimates that because of the higher birth rate of women older than 35 years combined with the decrease in the number of women aged 20 to 29 years, the proportion of babies born to these older women has almost doubled by the end of the 1990s compared with the early 1980s. Specifically, as noted by Eastman [24], the proportion of total births in women over 35 years of age has increased from 5% in 1982 to 8.6% in the year 2000. Thus, the impact of older maternal age on pregnancy becomes increasingly important.

Maternal age as a risk factor in pregnancy has a long history, but maternal age as a risk factor for shoulder dystocia has not received great emphasis. The significance of increasing age here is its relationship to increasing birthweight, diabetes, and obesity. In the mnemonic that helps to predict macrosomia, A DOPE, A refers to maternal age, which is associated with increased fetal birthweight as maternal age advances. The mature gravida over age 30 is at much greater risk for macrosomia and therefore shoulder dystocia. She is also at increased risk for obesity, diabetes, and excessive weight gain, as well as postdatism or a postterm gestation.

The definition of advanced maternal age in the obstetric literature is varied. Most authors have designated a lower limit of 35 years, others, 40 years, and a few have even indicated that 45 years represents advanced maternal age. Regardless of the specific age definition, pregnancies in women of advanced maternal age are considered by many to be high risk.

Generally, the incidence of most chronic illnesses increases as a function of age; it is not surprising, therefore, that medical complications are encountered more frequently in women who are older than 35 years. It follows logically that the severity and associated complications of many of these conditions increase, as does their duration, and thus it is likely that older pregnant women will have more advanced forms of chronic disorders. Perhaps the best example is diabetes, the incidence of which increases with age, and most type II, or non–insulin-dependent, diabetics are age 40 or older.

Using a computerized database from a perinatal network, 511 pregnancies in women whose age was 40 years or older at delivery were studied by Spellacy [20]. The oldest woman was aged 52 years. This group represented 1.2% of the 41,335 women delivering. Their pregnancy outcomes were compared with those of 26,759 women whose ages at delivery were 20 to 30 years. The older women were of greater parity and had higher weights. There was also an increased frequency of hypertension, diabetes mellitus, and placenta previa in the older women [24].

Spellacy showed [20] that the older women experienced an increase in infant macrosomia, male sex, stillbirths, and low Apgar scores. They also had a higher incidence of cesarean section and fewer forceps deliveries. The older women whose individual weights were less than 67.5 kg at delivery did not show any difference in hypertension, fetal macrosomia, fetal death rates, or low infant Apgar scores.

The results of the Spellacy study [20] confirm many earlier reported observations. The frequency of pregnancy in older women (>40 years) in this study was 1.2%, which is similar to that reported by others. The older women were of higher weight and had an increased frequency of both hypertension and diabetes mellitus. These factors most probably contributed to the increased frequency of cesarean section in older women.

The impact of maternal age is also noted in infant outcomes. Thus, older women have heavier infants with significant increases in macrosomia, low Apgar scores, and fetal deaths. When maternal obesity is removed as a factor, there are no differences in maternal hypertension, macrosomia, fetal deaths, and Apgar scores. Older women more frequently have male infants, shoulder dystocia, and brachial plexus injuries. Although advanced maternal age may have an adverse effect on pregnancy and delivery, the major impact seems to be related to the effect of increased weight and parity rather than to age itself.

As studies have shown, mature gravidas, age 30 years and over, can be expected to be heavier and have more macrosomic infants, with a concomitant risk for shoulder dystocia. The risk for macrosomia with increasing maternal age is as follows:

Table 1

It is difficult to separate maternal gestational diabetes, obesity, and antenatal weight gain from the age factor. The clinician must be aware that older mothers are at risk for increased fetal weight. This awareness should trigger more thorough nutritional counseling, fastidious measurement of fetal growth, liberal use of ultrasound, careful checking for maternal glucose intolerance, and strict control of antenatal weight gain.

The overwhelming majority of studies in the obstetric literature describe a significantly higher rate of cesarean births in older women. Kirz et al. [15] noted an increased use of cesarean delivery for the older age group. No one specific indication for cesarean birth showed an increase in the pregnancies of women over 34 years of age. It may be that the increase is cesarean births for older women is a self-fulfilling prophecy. Because the pregnancies have been considered high risk, the physician may use a lower threshold for terminating the labor process. Pregnant women of advanced maternal age received epidural anesthesia significantly more often than did younger parturients. This may be a contributing factor to the higher rate of forceps and vacuum deliveries for the older age group and to the incidence of shoulder dystocia and birth injury.

1.4 Maternal Height

It is a well-known fact that short obstetric patients have more difficult and prolonged labor. The risks of shoulder dystocia and cesarean section are higher among short women, particularly those with large fetuses, than among tall women.

In a study of 7,543 low-risk women, short stature (less than 5 feet 2 inches) was associated with nearly a doubling in the risk of cesarean section among women delivering their first child (odds ratio 1.72) as well as multiparous women (odds ratio 2.09). Tall stature (more than 5 feet 5 inches) halved the risk in first deliveries (odds ratio 0.42). Tallness had no impact on subsequent births, whose risk of cesarean section (odds ratio 1.01) was about the same as that of average-height women (5 feet 2 inches to 5 feet 4 inches).

On the basis of these results, physicians should consider the timely and judicious use of cesarean section in short women. Short women also had nearly twice the risk of shoulder dystocia (odds ratio 1.8) compared with that of tall women (odds ratio 0.58).

Absolute weight gain, regardless of height, also had an impact. The authors determined that when weight gain was over 35 lb, there appeared to be an increase in the risk of adverse outcomes. Height however, did not modify the effect of weight gain on outcomes [25].

1.5 Obesity

Maternal obesity is a very serious obstetric risk factor. In a discussion of shoulder dystocia or macrosomia, it must be given strong emphasis. It may have greater importance than does diabetes mellitus. Over the past 15 years, Americans have significantly increased their annual consumption of food from as much as 600 lb per year to more than 700 lb per year, and thus obesity is on the increase.

The literature supports a relationship between obesity and coexisting medical illnesses such as diabetes and hypertension. Perinatal adverse outcomes include an increased incidence of stillbirth and congenital anomalies. There is also an established relationship between maternal obesity and fetal macrosomia [26]. Since 1991, there has been a 50% to 70% increase in the rate of obesity in adults of reproductive age [2].

There is strong evidence for the relationship between macrosomia and shoulder dystocia; current case-control studies have demonstrated a higher prevalence of obesity in pregnancies affected by shoulder dystocia than in the corresponding control group [26].

In this large, prospectively collected cohort, it was found that obese and morbidly obese patients were at increased risk for gestational diabetes. The incidence of gestational diabetes in both obese (6.3%) and morbidly obese (9.5%) patients was increased compared with the control group (2.3%). These findings are consistent with previous studies. Creasy and Resnick [27] reported the incidence of gestational diabetes to be 24.5% for patients with a body mass index (BMI) greater than 40 compared with 2.2% for patients with a BMI of 20 to 24.9 (P < .0001). These authors reported an incidence of gestational diabetes of 14.2% for patients with a BMI greater than 35 compared with 4.3% for patients with a BMI of 19 to 27 (P < .01). for nulliparous patients, the cesarean delivery rate was 20.7% for the control group, 33.8% for obese, and 47.4% for morbidly obese patients [28].

The relationship between maternal size and fetal size is interesting. These findings confirm this association. These authors [28] found that both obese and morbidly obese patients have a significantly increased risk for birthweight greater than 4,500 g compared with controls. These findings are important to remember when clinically estimating fetal weight in the labor room. The clinician should know that a large fetus is more common in the obese and morbidly obese population.

Obese patients may have difficulty completing the second stage of labor secondary to soft tissue dystocia, and operative vaginal delivery may be used to expedite delivery in such a situation. After controlling for birthweight, the current study found that morbidly obese patients were more likely to have an operative vaginal delivery than were patients with a BMI less than 30. However, once again the odds ratio was less than 2.0 [28].

The effect of obesity alone was investigated by Garbaciak et al. [29] among 16,858 women who delivered their infants within a 12-month period. Complete analysis was possible for 9,667 patients, who were divided into four weight categories and separated into two groups, those with and those without complications. Perinatal mortality, infant size, and the primary cesarean delivery rate were calculated for each group. Among 2,597 women with prenatal complications, there was a significant increase in perinatal mortality (P < .001), primary cesarean delivery (P < .02), and mean infant birth weight (P < .01) in the obese and the morbidly obese gravid women. Obesity alone did not appear to affect the perinatal mortality rate, but it increased the likelihood of cesarean delivery in the morbidly obese patient, shoulder dystocia, and brachial plexus palsy.

In addition to careful measurement of fetal growth and fundal height measurements, the liberal use of ultrasound measurements in obese women is clearly indicated. The early identification of risk factors will permit early therapy, which should include careful dietary counseling, repeated blood sugar measurements, and weight restriction. Anticipation of the need for abdominal delivery should be noted early. Liberal use of labor induction may be helpful, as well as ultrasound measurements of fetal size at term. The recognition of a macrosomic child in the obese mother requires diligent search for any additional risk factors for shoulder dystocia, if vaginal delivery is considered. Cesarean section is indicated if these factors exist. Inability to evaluate the pelvis in such circumstances may justify imaging pelvimetry and/or consultation. The presence of macrosomia of 4,500 g alone is justification for cesarean section in nonobese women. The presence of macrosomia of 4,000 to 4,500 g may in itself be sufficient to warrant abdominal delivery when other risk factors, especially a platypelloid (flat) pelvis, diabetes, and/or obesity, are present.

Johnson and coauthors [30] recently reviewed the complications of pregnancy in 588 obese women who weighed at least 113.6 kg (250 lb) during pregnancy and in a matched control group of women who weighed less than 90.0 kg (200 lb) during pregnancy. The investigators noted that the incidence of pregnancy complicated by obesity more than doubled during the 20-year time interval of the study. The rates of diabetes and hypertension were significantly higher in the obese group (9.9% and 27.6%, respectively) than in the control group (2.2% and 3.1%, respectively). Therapeutic induction of labor was more common for the obese patients (23.5%) than in the control group (2.2%). The rate of failure of attempted inductions was significantly greater in the obese group (1%) than in the control group (1.5%). The indications for induction in the obese group included postdatism, hypertension, preeclampsia, diabetes, and premature rupture of the membranes without effective labor.

Shoulder dystocia occurred approximately twice as often in the morbidly obese patient without prenatal complications (1.78%) when compared with the normal-weight patient (0.81%) [30]. More recent data suggest that a significant increase in cesarean deliveries is present as a function of maternal obesity. If obese gravid women are at increased risk for prenatal complications, this increase in primary cesarean deliveries could be expected. However, between each weight category in those patients without prenatal complications, a significant increase in the number of cesarean sections was present for those patients who were morbidly obese.

Previous reports have concluded that fetal weight is directly proportional to maternal size. Emerson [31] reported that more than 50% of overweight women had babies who weighed over 8 lb (3,630 g). Eastman and Jackson [24] have shown a straight-line correlation between weight of the newborn infant and maternal weight gain in pregnancy of more than 10 lb. They also showed a direct correlation between prepregnant maternal weight and eventual infant birthweight. They believed that these two factors acted independently and additively in determining the baby’s weight and concluded that mothers who are heavier prior to conception will deliver heavier babies. Others have not only reported a significant increase in macrosomic babies in obese populations but have also noted a significant lengthening of the gestational period [20–23].

These data reveal a significant difference in mean infant birthweight among obese patients both with and without prenatal complications. As the weight of the mother increases, so does the weight of the newborn infant. Analyzing the correlation of fetal weight with maternal weight revealed that only 24% and 27% of the increase in fetal weight in women with and without prenatal complications, respectively, could be attributed to maternal weight alone. This tendency for increased birthweight as maternal weight increased was also present in those women who had prenatal complications.

Gross et al. [4] recently reported a higher incidence of macrosomic babies in their population of obese women. If this increase of macrosomia is present, it could serve as an explanation for the increase in primary cesarean sections, although this was not found in the study of Gross et al. This difference between studies may be due to the different way obesity was defined in their study and in the aforementioned British study [3] and the fact that Gross et al. did not differentiate obese women from morbidly obese women.

The best way to prevent the problems associated with morbidly obese and obese gravid women would be to eliminate the prepregnant obese state. Because this is not realistically possible, it is necessary for those attending such patients to be aware of the specific complications that can occur. This author recommends that all obese and morbidly obese gravid women have a glucose screening test for diabetes at their initial prenatal visit, and that it be repeated at the beginning of the third trimester, if the previous screen was normal. It seems prudent to avoid vaginal delivery in the morbidly obese patient who is at risk for any type of dystocia that is not easily correctable.

1.6 Obesity and Diabetes

The problems of maternal obesity are difficult to separate from gestational diabetes or overt diabetes; however, Johnson and colleagues [30] reported that in pregnant women weighing more than 250 lb, the incidence of shoulder dystocia was 5.1% compared with 0.6% for control women who weighed less than 200 lb. Spellacy and co-workers [20] reported that for women weighing more than 90 kg, infant birthweight distribution was as follows: 8.2% weighed 2,500 to 3,499 g, 33% weighed 4,500 to 4,999 g, and 50% weighed more than 5,000 g. Shoulder dystocia was identified in 0.3% of the 2,500 to 3,499 g infants, 7.3% of the 4,500 to 4,999 g infants, and 14.6% of the larger infants. Parks and Ziel [32] reported that when maternal prepregnancy or early pregnancy weight was above 90 kg, 5.5% of infants weighed more than 4,500 g compared with 1.9% in a control group. Shoulder dystocia was identified in 13.6% of infants who weighed more than 4,500 g compared with 1.7% in the control group.

The association of macrosomia with mild diabetes mellitus is well established and in the studies discussed above was a significant contributing factor in shoulder dystocia and brachial plexus injury [27].

1.7 Conclusion

Maternal age over 30 years, maternal obesity and height, as well as high maternal birthweight are significant risk factors for macrosomia, and thus the risk of shoulder dystocia is increased in this population. Identification of an abnormal pelvis in these women is critically important.

References

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Tracy T, Miller G. Obstetric problems of the massively obese. Obstet Gynecol 1969;33:204–209.PubMed

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Jovanovic L, Peterson C. Screening for gestational diabetes. Diabetes 1985;34:21–26.PubMed

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Leikin E, Jenkins J, Pomerantz G, Klein L. Abnormal glucose screening tests in pregnancy: A risk factor for fetal macrosomia. Obstet Gynecol 1987;69:570–74.PubMed

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Gabbe S, Mestman J, Freeman R, Anderson G, Lowensohn R. Management and outcome of class A diabetes mellitus. Am J Obstet Gynecol 1977;127:465–469.PubMed

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Grimes D, Gross G. Pregnancy outcomes in black women aged 35 and older. Obstet Gynecol 1981;58:614–618.PubMed

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Kajanoja P, Widholm O. Pregnancy and delivery in women aged 40 and over. Obstet Gynecol 1978;51:47–53.PubMed

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Kirz D, Dorchester W, Freeman R. Advanced maternal age: The mature gravida. Am J Obstet Gynecol 1985;152:7–11.PubMed

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Lehman D, Chism J. Pregnancy outcome in medically complicated and uncomplicated patients aged 40 years or older. Am J Obstet Gynecol 1987;157:738–744.

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Martel M, Wacholder S, Lippman A, Brohan J, Hamilton E. Maternal age and primary cesarean section rates: A multivariate analysis. Am J Obstet Gynecol 1987;156:305–310.PubMed

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Mestman J. Outcome of diabetes screening in pregnancy and perinatal morbidity in infants of mothers with mild impairment in glucose tolerance. Diabetes Care 1980;3:447–451.PubMed

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Modanlcu H, Dorchester W, Thorosian A, Freeman R. Macrosomia—maternal, fetal and neonatal implications. Obstet Gynecol 1980;55:420–426.

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Spellacy W, Miller M, Winegar A, Peterson P. Macrosomia—maternal characteristics and infant complications. Obstet Gynecol 1985;66:158–162.PubMed

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Yasin S, Beydoun S. Pregnancy outcome at greater than or equal to 20-weeks gestation in women in their 40 s. A case control study. J Reprod Med 1988;33:209–212.PubMed

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Klebanoff M, Mills J, Berendes H. Mothers birth weight as a predictor of macrosomia. Am J Obstet Gynecol 1985;153:253–258.PubMed

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Coustan D, Widness J, Carpenter M, Rotondo L, Pratt D, Oh W. Should the fifty gram, one hour plasma glucose screening test for gestational diabetes be administered in the fasting or fed state? Am J Obstet Gynecol 1986;154:1031–1035.PubMed

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Eastman N, Jackson E. Weight relations in pregnancy. Obstet Gynecol Survey 1968;23:1003–1024.CrossRef

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Gurewitsch E, Johnson E, Hamzehzadeh S, Allen R. Am J Obstet Gynecol 2006;194:486–492.PubMedCrossRef

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James A. O'Leary (ed.)Shoulder Dystocia and Birth Injury3Prevention and Treatment10.1007/978-1-59745-473-5_2© Humana Press, a part of Springer Science+Business Media, LLC 2009

2. Antepartum Risk Factors

James A. O’Leary¹ 

(1)

Professor Obstetrics & Gynecology (retired), University of south Florida, Tampa, Florida, USA

2.1 Introduction

2.2 Gestational Diabetes and Borderline Diabetes

2.3 Overt Diabetes

2.4 Postdate Pregnancy

2.5 Obesity

2.6 Excessive Weight Gain

2.7 Fundal Height

2.8 Conclusion

References

Summary

Identification of risk factors allows anticipation of shoulder dystocia and prevention of brachial plexus palsy. Obesity, diabetes, and increased fundal height are the most important risk factors.

Keywords

brachial plexus palsydiabetesmacrosomiashoulder dystocia risk factors

2.1 Introduction

The majority of physicians believe that there is a constellation of antepartum and intrapartum clinical features that indicate a predisposition to shoulder dystocia. By recognizing these warning signs, the alert practitioner should be able to avert or manage a shoulder dystocia successfully in most circumstances [1].

The major risk factors for shoulder dystocia (Table 2.1), especially those that lead to fetal injury, are included in the mnemonic A DOPE: age, diabetes (including prediabetes), obesity, postdatism, and excessive weight gain [2–18].

Table 2.1

Antepartum Risk Factors

Other risk factors frequently mentioned, such as maternal birthweight, prior shoulder dystocia, multiparity, and a history of birth injury and/or stillbirth, must be incorporated into the clinical assessment of obstetric patients, during both the pregnancy and the intrapartum period [18–32].

A 1995 report of 16,471 births defined the key risk factors predictive of shoulder dystocia to be a birthweight in excess of 3,600 g, diabetes, lower social class, Indian origin, obesity, four prior births, and Pitocin (oxytocin, Parke-Davis, Indiana, USA) [19].

2.2 Gestational Diabetes and Borderline Diabetes

Pregnancy-induced glucose intolerance includes gestational diabetes and cases with one abnormal value or two borderline values on a 3-hour glucose tolerance test (GTT); it represents a significant risk factor for macrosomia and shoulder dystocia [20–25]. Gestational diabetes is carbohydrate intolerance induced by pregnancy. This definition excludes the possibility that glucose intolerance may have antedated pregnancy. Use of the diagnostic term gestational diabetes communicates the need for high-risk surveillance to third-party payers or others responsible for the financing of health care delivery and to convince women of the need for further testing postpartum. Gestational diabetes is a heterogeneous disorder with varied worldwide prevalence. Indeed, in a 10-year survey [21], the reported prevalence of gestational diabetes varied from 0.15% to 12.3%.

It is well-known that women with fasting hyperglycemia are at greater risk for fetal death and that this danger is not apparent for those with postprandial hyperglycemia only [26]. Today, the perinatal focal point is avoidance of difficult delivery due to macrosomia and of concomitant neonatal morbidity from birth trauma and shoulder dystocia with elevated fasting glucose.

2.2.1 Identification

The obvious advantage of identifying gestational diabetes is increased awareness of potential shoulder dystocia [22–29]. Bochner and colleagues [30] reported the outcomes of 201 gestational diabetics whose fasting and postprandial glucose values were normalized with diet. Fetal abdominal circumference was measured ultrasonically between 30 and 33 weeks. For infants with values over the 90th percentile, 40% weighed more than 4,000 g at delivery, and there was an increased incidence of cesarean section for failure to progress, shoulder dystocia, and birth trauma. Conversely, if the size of the circumference was below the 90th percentile, these complications were not increased compared with the normal population. The predictive value of abdominal circumference measurements greater than the 90th percentile was 56%, thus supporting the role of ultrasound.

It is emphasized that the pregnant woman with a normal fasting glucose level but an abnormal GTT early in pregnancy may develop overt diabetes late in pregnancy and be at increased risk for significant macrosomia. The incidence is estimated to be about 15%, and thus fasting glucose levels should be checked periodically.

All pregnant women should be screened for glucose intolerance in the second trimester. Patients at high risk should receive a repeat screen or its equivalent in the third trimester. The nonfasting 50 g glucose screen should be used. Values above 135 to 140 mg% are considered abnormal. At least 5% to 10% of the gestational diabetics and insulin-dependent patients will have infants who develop macrosomia. The presence of glucose excess, especially if the abnormal value is the fasting blood sugar, will greatly increase risk for shoulder dystocia, especially if any prepregnancy risk factors are present. In O’Shaughnessy’s series, approximately 50% of the diabetic pregnancies resulted in large for gestational age (LGA) infants [31].

The diagnosis of gestational diabetes is based on criteria originally proposed by O’Sullivan and Mahan [32], which include at least two abnormal values on a 3-hour oral GTT. The increased incidence of maternal and fetal complications among patients with gestational diabetes is now well established.

Of the 2,276 patients studied by Leikin et al. [20] who underwent screening for gestational diabetes mellitus, 81.5% had normal glucose screening tests after a 50 g carbohydrate load (serum glucose <135 mg/dL). Of the 15.7% who had abnormal glucose screening tests and went on to complete 3-hour GTT, 48.7% were shown to be nondiabetic when further tested with a 3-hour GTT. The 176 women with abnormal glucose screens but normal GTTs were compared with the 1,854 who had normal screening values. The frequency of infants weighing more than 4,000 g was 11.9% in the study group and 6.4% in the control group (P = .0086). When the data were corrected for other macrosomia risk factors (advanced age, multiparity, obesity, white race, and prolonged gestation), there was still a significantly higher frequency of macrosomia in the study group; this demonstrates that patients with minor abnormalities of carbohydrate metabolism during pregnancy are at risk for delivering a macrosomic infant. These results are similar to those of Frisoli et al. [28], who reported macrosomia in 6 infants of a group of 22 mothers who had an abnormal glucose screening but normal findings on GTT between the 30th and 34th weeks of gestation.

In the study of Al-Shawaf et al. [33] of 218 pregnant women with abnormal glucose tolerance, 81.2% had impaired glucose tolerance and 18.8% had gestational diabetes. Gestational diabetic women were of higher parity, more obese, required insulin therapy more often, had more babies weighing more than 4,000 g, and had higher fasting plasma glucose than women with impaired glucose tolerance. Women with gestational impaired glucose tolerance were older, more obese, of higher parity, and had heavier babies than did pregnant women with a normal screening plasma glucose.

It behooves all care providers to consider every obese patient as high risk for shoulder dystocia. The combination of obesity and diabetes makes these patients very high risk for shoulder dystocia, and thus the threshold for cesarean section should be reduced. Langer studied this association in 4,001 patients. He concluded that achievement of targeted levels of glycemic control was associated with enhanced outcome only in women treated with insulin [34]!

2.2.2 One Abnormal Value

All studies suggest that patients with minor abnormalities of carbohydrate metabolism during pregnancy are at risk for delivering a macrosomic infant [35]. Pregnant patients of the type identified in these studies benefit from dietary control and more intensive evaluation of their fasting and postprandial glucose levels. It is necessary to determine whether such measures would prevent the increased incidence of macrosomia in this population and thus limit the potential morbidity of mothers and their infants.

In a report by Lindsay et al. [36], the presence of either a single abnormality on the oral GTT or an abnormal glucose screen was associated with an increased risk of pregnancy complications. It was clear