Socioeconomic status as a modifier of the relationship between antibiotic use during pregnancy and birthweight

Antibiotics taken during pregnancy treat underlying maternal infections that may otherwise contribute to poor birth outcomes, including decreased birthweight. This study investigated whether antibiotics taken by a diverse sample of North American women were associated with increased mean infant birthweight and whether this relationship was modified by socioeconomic status. The study hypothesized that women of low socioeconomic status, whose babies are at highest risk of low birthweight perhaps due to long-standing undiagnosed infections, might benefit from antibiotic use more than women of higher socioeconomic status.

The sample was 868 control women from a case-control study of hemifacial microsomia, a craniofacial birth defect. Participants reported information on antibiotic use during pregnancy (type, indication, and timing) and baby's birthweight in telephone interviews.

Nineteen percent of women reported taking at least one antibiotic in the first half of pregnancy, but average birthweights were similar among users and nonusers. However, low-socioeconomic status women who reported taking antibiotics to treat genitourinary infections had babies that were 286 g heavier than those who did not (p = 0.01). No association was seen among higher socioeconomic status women. Differences by socioeconomic status were also seen in treatment for respiratory conditions and use of penicillin antibiotics.

These findings suggest that socioeconomic status might modify the association between antibiotics taken during pregnancy and infant birthweight. They emphasize the need to consider socioeconomic status in studies of antibiotic use and birth outcomes and extend previous studies of socioeconomic disparities in birth outcomes.