Absence of transplacental passage of the low molecular weight heparin enoxaparin

Background: Venous thromboembolism (VTE) during pregnancy and puerperium remains a major cause of maternal morbidity and mortality. The use of low molecular weight heparin (LMWH) constitutes a promising alternative for the prevention of VTE instead of unfractionated heparin as it can be administered subcutaneously once daily and without coagulation measurement. Unfortunately, the safety of LMWHs administration for the mother and fetus has not been well established. Study Design: In order to examine the safety of enoxaparin to the fetus, 24 women were recruited and 40 mg of enoxaparin was administered in 14 of them. All 24 women were going to have an early termination of pregnancy due to major fetal malformations. Maternal blood samples were drawn before and after the injection of enoxaparin, while fetal blood samples were taken only after the drug administration. Anti-IIa and anti-Xa activities were measured. Results: A statistically significant increase of anti-Xa activity in the mothers studied was pointed out, while there was no detection of anti-IIa and anti-Xa activities in the fetuses. Conclusions: Since no anti-IIa and anti-Xa activities were detected in the fetuses' blood samples, it is concluded that enoxaparin does not cross the placenta and therefore appears safe for the fetus. Copyright (C) 2001 S. Karger AG, Basel.