Use of metronidazole and incidence of birth defects

American Family Physician,  Jan, 1994  

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Metronidazole is widely used to treat vaginal and cervical infections in patients who are not pregnant. It has not been recommended for use in pregnant women because of concerns about teratogenicity. These concerns are based on animal studies supported by case reports and a few human studies that had significant biases and design problems. Since infections that are usually treatable with metronidazole have been implicated in premature labor, the ability to use this drug safely during pregnancy could significantly reduce adverse pregnancy outcomes, particularly in high-risk mothers. To document any association between metronidazole and birth defects, Piper and colleagues studied the outcome of pregnancies in women who used metronidazole during pregnancy.

Medicaid data were used to identify low-income pregnant women aged 15 to 44 years who filled a prescription for metronidazole between 30 days before and 120 days after the last menstrual period. Data were gathered from birth certificates and other sources regarding pregnancy outcome in the women who used metronidazole during pregnancy. These outcomes were compared with those in women who did not fill a metronidazole prescription during early pregnancy. Each exposed woman was matched with one control subject by race, age, hospital and year of delivery. The staff gathering and classifying data on pregnancy outcomes were blinded as to the exposure status of each mother.

Each group included 1,387 mothers, and the two groups were comparable in terms of race, age, parity, level of education, and rural or urban residence. Women with exposure to metronidazole were less likely to be married than women without exposure, but they were significantly more likely to have begun prenatal care in the first trimester and to have more prenatal visits.

No differences were found between the metronidazole group and the control group in terms of very low birth weight, fetal viability at birth or rates of multiple birth. Eight stillbirths occurred in the non-exposed group, compared with four in the exposed group. Although 96 birth defects occurred in infants of exposed women and 80 in infants of nonexposed women, this difference was not statistically significant and the risk ratio was 1.2. Detailed examination of birth defects by category did not show any pattern of excess defects in infants exposed to metronidazole.

The authors conclude that use of metronidazole during pregnancy had neither an overall effect nor a specific effect on one or more fetal organ systems. No evidence was found to indicate that birth defects are attributable to metronidazole use in early pregnancy.

COPYRIGHT 1994 American Academy of Family Physicians
COPYRIGHT 2008 Gale, Cengage Learning