Do Anti-Factor Xa Levels have any Impact on Pregnancy Outcome in Women with Previous Adverse Outcomes?

Objective Low-molecular-weight heparin (LMWH) is used during pregnancy in women diagnosed with thrombophilia for prevention of thromboembolic events and prevention of recurrent pregnancy loss. Prophylactic dosing does not always achieve target anti-FXa levels of 0.2-0.6 IU/ml. We aimed to determine if anti-FXa levels, measured in the first trimester, have an influence on pregnancy outcome. Material and Methods Eighty-one first-trimester women with a history of adverse pregnancy outcomes under LMWH therapy during pregnancy were enrolled in this study. Anti-FXa levels were measured in the first trimester, and fetal and maternal outcomes were recorded. Results The mean age of women was 28 +/- 4 (19-40) and mean anti-FXa level 0.44 +/- 0.93 IU/ml. No bleeding or clotting complications were associated with LMWH administration. Anti-FXa levels did not have a relationship with gestational age at birth, fetal weight, type of delivery, cesarean indications, postpartum bleeding, APGAR scores, or admission to the neonatal intensive care unit (p > 0.005). Anti-FXa levels were not correlated with live birth rates. Conclusion Anti-FXa levels did not have an influence on pregnancy and fetal outcomes. The effect of LMWH on pregnancy outcomes may not be due to anticoagulant activity but other mechanisms.