Prospective associations between household secondhand smoke exposure across critical developmental windows and early childhood caries: a birth cohort study.

BACKGROUND: Early childhood caries (ECC) is preventable, and household secondhand smoke (HSHS) is a modifiable risk factor. However, evidence regarding critical early-life exposure windows and potential sex differences in the association remains limited. OBJECTIVE: To examine the associations between HSHS exposure from early fetal life to 24 months of age and ECC in preschool children, and to explore potential sex differences. METHODS: Data from 2,431 mother-child pairs in the Shanghai Maternal-Child Pairs Cohort were analyzed. HSHS exposure was self-reported during early and late pregnancy and at 2, 6, and 24 months of age. ECC was clinically diagnosed at 3-5 years of age. Group-based trajectory modeling identified HSHS exposure patterns, and Cox proportional hazards models estimated associations between HSHS exposure and ECC. RESULTS: Three distinct HSHS exposure trajectories were identified: Never Exposure (31.8%), Prenatal Decline-Postnatal Rebound (40.5%), and Persistently High Exposure (27.7%). Children in the latter two trajectories had a higher risk of ECC compared with those in the Never Exposure group (adjusted HR=1.23, 95% CI: 1.01-1.49; and adjusted HR=1.36, 95% CI: 1.12-1.66, respectively). Exposure at all assessed time points was associated with increased ECC risk, with the strongest associations observed during early pregnancy and at 24 months. Sex-stratified analyses showed significant associations among girls but not among boys. CONCLUSION: Early-life household secondhand smoke exposure was associated with an increased risk of early childhood caries in the overall study population, with significant associations observed among girls but not boys in sex-stratified analyses. CLINICAL SIGNIFICANCE: Assessment of household secondhand smoke exposure during early life may provide useful information for caries risk assessment and oral health counseling in preschool children.