Absence of transplacental passage of the low molecular weight heparin enoxaparin

Background: Venous thromboembolism (VTE) during pregnancy and puerperium re mains a major cause of maternal morbidity and mortality. The use of low mol ecular weight heparin (LMWH) constitutes a promising alternative for the pr evention of VTE instead of unfractionated heparin as it can be administered subcutaneously once daily and without coagulation measurement. Unfortunate ly, the safety of LMWHs administration for the mother and fetus has not bee n well established. Study Design: In order to examine the safety of enoxapa rin to the fetus, 24 women were recruited and 40 mg of enoxaparin was admin istered 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 samp les were taken only after the drug administration. Anti-IIa and anti-Xa act ivities were measured. Results: A statistically significant increase of ant i-Xa activity in the mothers studied was pointed out, while there was no de tection of anti-IIa and anti-Xa activities in the fetuses. Conclusions: Sin ce no anti-IIa and anti-Xa activities were detected in the fetuses' blood s amples, it is concluded that enoxaparin does not cross the placenta and the refore appears safe for the fetus. Copyright (C) 2001 S. Karger AG, Basel.