Maternal oral health indicators during pregnancy and childhood allergic outcomes up to three years: a retrospective analysis of a prospective cohort study

Abstract

Maternal oral health during pregnancy may be associated with offspring allergic outcomes, but evidence linking specific oral health indicators to childhood allergy is limited. We examined associations between maternal oral health indicators during pregnancy and questionnaire-ascertained asthma, allergic rhinitis, eczema, and food allergy in children up to three years of age, with particular attention to effect modification by maternal atopy. We conducted a retrospective analysis of data from the Yazd Mother-Infant Health Cohort (2016–2019) in Iran. A total of 3,110 mother-child pairs had complete maternal oral health and covariate data at baseline and constituted the exposure cohort. Because childhood allergic outcomes could only be analysed in children with follow-up data, the outcome analyses were restricted to 1,752 children with at least one outcome assessment at age 2 or 3 years and, for the analyses stratified by maternal atopy and for the baseline characteristics presented in Table 1, to the 1,113 children (35.8% of the baseline cohort) assessed at age 3 years. Maternal oral health indicators assessed in early pregnancy included the clinically assessed decayed, missing, and filled teeth (DMFT) index, self-reported total number of teeth, tooth brushing frequency, dental floss use, and gingival bleeding. Childhood outcomes were ascertained through standardized cohort questionnaires administered to parents at ages 1, 2, and 3 years and were not independently confirmed by clinical examination. Modified Poisson regression with robust standard errors was used to estimate adjusted risk ratios (RR) for ever-reported outcomes by age 3 years. Longitudinal associations were examined using generalized estimating equations (GEE). Effect modification by maternal atopy history was assessed using interaction terms. Among the 3,110 mothers of the baseline exposure cohort, the mean DMFT index was 10.63 (SD 6.85), comprising 2.34 decayed (SD 3.02), 3.35 missing (SD 4.84), and 5.61 filled teeth (SD 4.48). Mean tooth brushing frequency was 3.02 times/day (SD 1.17). Among the 1,752 children with at least one follow-up assessment at age 2 or 3 years, ever-reported childhood allergic outcomes by age three were 10.8% for asthma, 5.6% for allergic rhinitis, 7.8% for eczema, and 16.9% for food allergy. The association between maternal DMFT and questionnaire-ascertained allergic rhinitis was significantly modified by maternal atopy history (interaction p=0.008). In these analyses, which were based on the 1,113 children with an age-3 assessment, higher DMFT was associated with an increased risk of allergic rhinitis among mothers with atopy (n=387; adjusted RR per 1 SD increase =1.56, 95% CI 1.09-2.24, p=0.016), whereas an inverse association was observed among mothers without atopy (n=726; adjusted RR=0.77, 95% CI 0.60-0.99, p=0.042). Maternal DMFT was not significantly associated with ever-reported food allergy by age three years (RR=1.13, 95% CI 0.98–1.30, p=0.096). In longitudinal GEE analysis, higher DMFT was associated with increased risk of questionnaire-ascertained food allergy (RR=1.28, 95% CI 1.09–1.50, p=0.002). No significant associations were observed between maternal DMFT and asthma or eczema, nor between maternal oral hygiene behaviors and allergic outcome. Higher maternal DMFT was associated with questionnaire-ascertained allergic rhinitis differently according to maternal atopy history. The association between maternal DMFT and ever-reported food allergy by age three was not statistically significant, although a positive association was observed in the longitudinal analysis. Given the questionnaire-based ascertainment of childhood allergic outcomes, the restriction of the outcome analyses to the minority of the baseline cohort with follow-up data (1,752 of 3,110 pairs, and 1,113 at age 3 years), and multiple comparisons, these findings should be interpreted cautiously and require replication using clinically assessed oral health and objectively defined allergic outcomes.