In utero exposure to steroid contraceptives and outcome of pregnancy.

A cohort study of women who used steroid contraceptives during pregnancy was conducted in Chiang Mai, northern Thailand, between 1984 and 1987. There were 1,573 pregnancies in which the fetus was exposed to the injectable contraceptive Depo-Provera (The Upjohn Company, Kalamazoo, Michigan) (830 accidental pregnancies and 743 infants conceived before the mother started use of Depo-Provera), 601 accidental pregnancies in women who were using oral contraceptives, and 2,578 planned pregnancies with no steroid exposures (controls). Subjects were followed up for interview, and medical records were traced for birth weight. Women using Depo-Provera had more risk factors for adverse pregnancy outcomes than did the other groups. The adjusted odds ratios for low birth weight were increased for accidental pregnancies with fetal exposure to Depo-Provera (odds ratio (OR) = 1.5, 95% confidence interval (Cl) 1.2-1.9) or oral contraceptives (OR = 1.5, 95% Cl 1.2-2.0). The higher risk of low birth weight among infants exposed in utero to Depo-Provera or oral contraceptives is due in part to self-selection for adverse outcomes among women with unplanned pregnancies. However, among accidental pregnancies with Depo-Provera, the risk of low birth weight was significantly increased when conception was estimated to have occurred within 4 weeks of injection. The odds ratios were 1.9 (95% Cl 1.4-3.2) for injection-to-conception intervals of less than or equal to 4 weeks, 1.5 (95% Cl 0.9-2.3) for intervals of 5-8 weeks, and 1.2 (95% Cl 0.7-1.9) for intervals of greater than or equal to 9 weeks. This trend was highly significant. Thus, the authors conclude that early, high-dose in utero exposures to Depo-Provera may affect fetal growth.