OBJECTIVE: Our purpose was to investigate the use of low-molecular-weight heparin (enoxaparin, Clexane) for thromboprophylaxis in pregnancy.

STUDY DESIGN: A prospective consecutive cohort of 61 pregnant women at high risk of thromboembolism receiving antenatal thromboprophylaxis with enoxaparin (usually 40 mg, subcutaneously daily) in a total of 69 pregnancies was identified from the obstetric medicine clinic at Queen Charlotte's Hospital. Bone density measurements of the hip and lumbar spine were taken in 26 women after 28 pregnancies within 16 months post partum. Nonparametric statistics were used for comparisons.

RESULTS: There were no episodes of antenatal thromboembolism. One woman (1.6%) (receiving 20 mg of enoxaparin) had a pulmonary embolus post partum. Heparin levels (anti-Xa assay) were greater with the 40 mg dose (median 0.09 U/ml) than with the 20 mg dose (median 0.03 U/ml) (p = 0.0006) but were not affected by gestational age (r = –0.1, p = 0.14). Enoxaparin had no effect on platelet count or on in vitro coagulation tests. Nine (32%) women had bone density in the spine or hip >1 SD below the mean for age- and sex-matched controls.

CONCLUSION: This, the largest study to date of low-molecular-weight heparin use in pregnancy, confirms previous reports that it is a safe and effective alternative to unfractionated heparin for obstetric thromboprophylaxis in high-risk women. Effects on bone demineralization require further investigation. (Am J Obstet Gynecol 1997;176:1062-8.)