ABO Fetomaternal Compatibility Poses a Risk for Massive Fetomaternal Transplacental Hemorrhage

Abstract

In the third trimester, fragility of the placental membrane increases the risk of fetomaternal transplacental hemorrhage (FMH), which can result in severe fetal anemia from the hemorrhage itself or from the subsequent effects of isoimmunization. ABO incompatibility between the mother and fetus is associated with a significantly reduced risk of isoimmunization. The investigators hypothesized that this protective effect might be due to reduced risk of fetomaternal hemorrhage in ABO incompatible mother-fetus pairs, and that ABO compatible pairs might be at increased risk of fetomaternal hemorrhage. Investigators evaluated 8 cases of severe fetomaternal transfusion identified among 17,000 deliveries at a tertiary care center between 2003 and 2007. Blood group compatibility between the mother and fetus was evaluated and the perinatal outcome assessed. The Kleihauer-Betke test was used to diagnose FMH. The mean gestational age in the study population was 35 weeks (range 32–39) and the mean fetal weight was 2750 gm (range 2140–3420). All deliveries were operative. Among the 8 infants, 6 (75%) had adverse outcomes after FMH. Four of the infants were affected by posthypoxic damage of varying severity, and there were 2 perinatal deaths. Seven of the 8 cases had fetomaternal ABO compatibility between the mother and fetus. These findings suggest that ABO compatibility between the mother and fetus significantly increases the risk of severe fetomaternal hemorrhage. For cases with severe fetal anemia, the investigators recommend that resuscitation in utero by intrauterine transfusion should be considered before the 33rd week of gestation.