3.3 Timing of prenatal antibiotic exposure and AD risk
Regarding the timing of prenatal antibiotic exposure and AD risk, the risk was slightly higher in the first trimester (aHR 1.04, 95% CI 1.03-1.05) and second trimester (aHR 1.03, 95% CI 1.01-1.04) than in the third trimester (aHR 1, 95% CI 0.99-1.01), in which the risk became non-significant. When the reference group was set as “no antibiotic use during the whole pregnancy”, the risk of AD was slightly increased in all three trimesters (first trimester: aHR 1.06, 95% CI 1.05-1.08, second trimester: aHR 1.06, 95% CI 1.05-1.07, and third trimester: aHR 1.04, 95% CI 1.02-1.05) (Table 4).