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).