Detection of anti-D following antepartum injections of Rh immune globulin

Antepartum prophylaxis using Rh immune globulin (RhIG) at 28 weeks of gestation is routine in unsensitized Rh-negative women. As various sources state that anti-D may be detected up to 6 months after administration, we reviewed the medical and laboratory records of all Rh-negative women who delivered at our institution during 1995. For 385 evaluable women, only 137 (35.6%) had anti-D demonstrable in their sera at delivery; 97.8 percent of these delivered within 75 days after administration of RhIG. Of 248 women (64.4%) who delivered in < 76 days after administration of RhIG, 134 (54%) had demonstrable anti-D. For 123 women who delivered between 76 to 95 days after RhIG, only 3 (2.4%) had demonstrable anti-D. Of 14 women who delivered more than 96 days after RhIG, none had anti- D at delivery. These data show that the 300-μg dose used in the United States may not be adequate for antepartum protection and that the detection of anti-D more than 100 days after the administration of RhIG should be viewed with suspicion.