Author: Dylan Luyten, M.D. Educational Pearls Rhogam is commonly used when an Rh negative woman has an Rh positive fetus. It is commonly used in the ER in the setting of a miscarriage. Rh(+) fetal blood can enter the Rh(-) maternal circulation, sensitizing the woman to the Rh antigen. During a subsequent pregnancy, if the fetus is Rh(+), the woman may mount an immune response to the fetus, lead to fetal demise. Rhogam is used to block this process. Use of Rhogam has reduced this complication from 16% of Rh(+) pregnancies in the 1960’s to less than 1% today. Under 10 weeks, the amount of maternal-fetal blood exchange is very small, so the use of Rhogam in a 1st trimester miscarriage is unnecessary. It should be used in patients with a miscarriage after 12 weeks, or women undergoing a surgical D&C. Rhogam is expensive and in limited supply, so it is important to only use it when necessary. References: Hannafin, Blaine et al. Do Rh-negative women with first trimester spontaneous abortions need Rh immune globulin? 2006.  The American Journal of Emergency Medicine, Volume 24 , Issue 4 , 487 - 489