The use of low molecular weight heparins (LMWH) such as enoxaparin as antithrombotic prophylaxis in women with pregnancy complications is controversial.

To evaluate the issue further, Jean-Christophe Gris, MD, University of Montpellier, Nimes, France, and colleagues conducted a prospective evaluation of the effect of thromboprophylaxis in women with one unexplained pregnancy loss from the 10th week of amenorrhoea.

A total of 160 patients, with heterozygous factor V Leiden mutation, prothrombin G20210A mutation, or protein S deficiency, were given 5 mg folic acid daily before conception, continued throughout pregnancy. The women were also given low-dose aspirin, 100 mg daily, or low-molecular weight heparin enoxaparin, 40mg, from the 8th week.

Of the 80 patients treated with low-dose aspirin, 23 had a normal live birth compared to 69 of the 80 patients treated with enoxaparin (OR 15.5 P < .0001). In addition, the neonate weight was higher in the women successfully treated with enoxaparin and neonates small for gestational age were more frequent in patients treated with low-dose aspirin.

According to the researchers, enoxaparin was superior to low-dose aspirin in each subgroup of thrombophilic disorder. Furthermore, protein Z deficiency and/or positive anti-protein Z antibodies were associated with poorer outcomes.

No significant side-effects of the treatments were seen in patients or newborns.

"This is the first study in which the outcome of antithrombotic-treated, constitutional thrombophilia-associated pregnancies in women with a clearly defined obstetric history is not compared to the patients' previous history of pregnancy loss but in which two antithrombotic treatments are prospectively compared," Dr. Gris and colleagues point out.

"As there is no argument to prove that low-dose aspirin may had been deleterious, these results support enoxaparin use during such at-risk pregnancies," the researchers suggest.