Lovenox pregnancy warning proves controversial. (Congenital Anomalies at Issue).

Recently issued precautions about congenital anomalies associated with Lovenox use in pregnancy should not dissuade doctors from prescribing the drug, but they should heed the warning not to use it in women with prosthetic heart valves, according to one expert.

Aventis, which manufactures the low-molecular-weight heparin (LMWH), sent a letter to health care professionals in February about additions to the drug's labeling information. According to the letter, congenital anomalies reported in infants born to women who received the drug during pregnancy include cerebral anomalies, limb anomalies, hypospadias, peripheral vascular malformations, fibrotic dysplasia, and cardiac defects. It also noted that a cause-and-effect relationship has not been established and that the incidence of these defects was no higher than in the general population.

The revised label also includes a warning that Lovenox (enoxaparin) is not recommended for use in patients with prosthetic heart valves because of an increased risk of valvular thrombosis.

But according to Dr. Charles Lockwood, the revised label should not prevent physicians from using the drug in most pregnant women. "There is no reason to change practice in any way except to avoid low molecular weight heparin in women with mechanical prosthetic heart valves," said Dr. Lockwood, professor and chair of obstetrics and gynecology at New York University, New York.

"The agent does not cross the placenta, providing no biological plausibility for such a risk. Secondly, a large study by Dr. J. Lepercq and associates [BJOG 108(1l):1134-40, 2001] described pregnancy outcomes in 604 women treated with enoxaparin and observed a congenital anomaly rate of only 2.5%. And lastly, the variety of anomalies reported by Aventis and their rare occurrence strongly suggests no specific malformation pattern or increased frequency," he said.

The American College of Obstetricians and Gynecologists has yet to issue an official position on use of LMWH in pregnancy and congenital defects but is considering the matter in detail, said Dr. Lockwood, chair of ACOG's Committee on Obstetric Practice.

A spokeswoman for Aventis in Bridgewater, N.J., said that the label revision was meant as "a precaution" and that the company is currently "in discussions to perhaps revisit the warning" and that "it might be toned down."