Hemophilia A is an X-linked, recessive disorder caused by deficiency of functional plasma clotting factor VIII (FVIII), which may be inherited or arise from spontaneous mutation. Because hemophilia is an X-linked, recessive condition, it occurs predominantly in males. Females usually are asymptomatic carriers. However, mild hemophilia has been described in female carriers.

Hemophilia B is much less common than hemophilia A. It is an inherited, X-linked, recessive disorder that results in deficiency of functional plasma coagulation factor IX. Because hemophilia is an X-linked, recessive condition, it occurs predominantly in males. Females usually are asymptomatic carriers and often have normal FIX levels.

Recently, Swedish Medical Birth Registry records were reviewed to determine if pregnant females who were hemophilia A and B carriers had an increased risk of bleeding or other maternal and neonatal complications. Data from 298 pregnancies in153 hemophilia A carriers and 51 pregnancies in 27 hemophilia B carriers was reviewed between the years of 1987 and 2013.

The study found that the risk of bleeding was more than three times higher in hemophilia B carriers than in non-carriers, but the risk for having other pregnancy complications, such as preeclampsia, preterm birth, low birth weight or low Apgar score was similar in both groups. In contrast, researchers found no differences in the risk of postpartum bleeding between hemophilia A carriers and non-carriers, or in the risk of complications during pregnancy or in the newborn.

The bleeding risk differences between hemophilia A and B carriers is most likely because factor VIII levels normally increase more than twofold during the third trimester of pregnancy, while FIX remains the same or only slightly increases. FVIII levels can also increase in female carriers of hemophilia A during pregnancy and reach normal levels. However, FIX levels in female carriers of hemophilia B remain low throughout pregnancy.

The authors recommended that factor VIII and IX levels should be checked during the third trimester of pregnancy. If clotting factors are too low, factor concentrate should be administered to reduce the risk of excessive bleeding during labor and delivery.

Reference

Olsson A et al. Maternal and neonatal outcomes in carriers of haemophilia A and B: A Swedish Medical Birth Register study. Haemophilia, 2019;00:1-4, https://doi.org/10.1111/hae.13884


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