Fetomaternal hemorrhage in normal vaginal delivery and in delivery by cesarean section.

Background: The objective was to determine the incidence and volume of fetomaternal hemorrhage (FMH) in normal vaginal delivery and in delivery by cesarean section. Determination of these variables would enable optimalization of guidelines for D alloimmunization prophylaxis.

Study Design And Methods: In a prospective cohort study, a total of 3457 examinations were performed, 2413 after normal vaginal delivery and 1044 after cesarean delivery. FMH was assessed by flow cytometry. (FMH is fetal red blood cell [RBC] volume; fetal blood volume is double [expected fetal hematocrit is 50%].)

Results: The fetal RBC volume diagnosed in maternal circulation after delivery ranged from insignificant FMH of not more than 0.1 mL to excessive FMH of 65.9 mL (median, 0.7; mean, 0.78; SD, 1.48). FMH of more than 2.5 mL (immunoglobulin [Ig] G anti-D insufficient dose 50 µg) was observed in 1.4% (49/3457) and excessive volumes of FMH of more than 5 mL (insufficient dose, 100 µg) in 0.29% (10/3457). Delivery by cesarean section presented a higher risk of incidence of FMH of more than 2.5 mL (odds ratio, 2.2; p = 0.004) when compared with normal vaginal delivery. It did not, however, present a significant risk factor for the incidence of excessive volumes of FMH of more than 5 mL.

Conclusion: During normal vaginal delivery as well as during delivery by cesarean section, FMH of less than 5 mL occurs in the great majority of cases, and thus for the prevention of D alloimmunization, an IgG anti-D dose of 100 µg should be sufficient. Contrarily, only rarely does greater FMH occur and delivery by cesarean section does not present a risk factor.