3.1 Demographic data of the study subjects
A total of 1288343 mother-child pairs were included in our study with a median follow-up time of 61 months, and the mean (SD) age of AD diagnosis was 0.81 ± 1.1 years old. The mean maternal age was 31.38 ± 4.6 years and 508647 (39.5%) received antibiotics during pregnancy. The prevalence of AD in our cohort was 22.3%, corresponding to the incidence rate of 3.69 (95% CI 3.68-3.71) per 1000 person-months. The frequency of maternal antibiotic use varied slightly during pregnancy, from 17.9% in the first trimester to 19.0% in the second and 14.6% in the third trimester.
As shown in Table 1, the infants of mothers exposed to prenatal antibiotics were more likely to be born preterm than infants of unexposed mothers, but there was no association with increased risk of AD (aHR 0.98, 95% CI 0.96-0.99) (Table 3). In contrast, prenatal acetaminophen exposure, gestational infections, and maternal atopic disorders, such as allergic rhinitis, and AD were positively associated with prenatal antibiotic use and AD risk (Table 1, Table 3). The exposure and unexposed groups were similar regarding childbirth year, sex distributions, birth weight, Apgar scores at birth, maternal age, urbanization, insurance properties, mode of delivery, type of pregnancy, and paternal age (Table 1). Infants born to mothers with prenatal antibiotic exposure were more likely to be exposed to postnatal antibiotics and acetaminophen than those born to unexposed mothers in the first year of life (Table 1). We performed a subgroup analysis that only included AD diagnosed after 1 year of age, as shown in Table 5, which still showed a positive association with AD in the prenatal exposure group, but the estimate was attenuated after adjusting for potential covariates and was even reduced to null in children who were not exposed to postnatal acetaminophen (aHR 1.02, 95% CI 0.97-1.07).