Maternal smoking during pregnancy and type 1 diabetes in the offspring: A nationwide register-based study with family-based designs

Objectives: Maternal smoking during pregnancy is associated with a reduced risk of type 1 diabetes (T1D) in the offspring. We investigated whether this association is consistent with a causal interpretation by accounting for familial (shared genetic and environmental) factors using family-based, quasi-experimental designs. Design: A nationwide, prospective cohort study and a nested case-control study (quasi-experiment) comparing children with T1D to their age-matched siblings (or cousins). Setting: Swedish national registers. Participants: We included 2,995,321 children born in Sweden between 1983 and 2014. Exposure: Information on maternal smoking during pregnancy was retrieved from the Swedish Medical Birth Register. Main outcome measures: Children were followed for a diagnosis of T1D until 2020 through the National Patient, Diabetes and Prescribed Drug Registers. Results: A total of 18,617 children developed T1D, with a median age at diagnosis of 9.4 years. The sibling and cousin comparison design included 14,284 and 7,988 of these children, respectively. Maternal smoking during pregnancy was associated with a 22% lower risk of offspring T1D in the full cohort (hazard ratio: 0.78, 95% confidence interval [CI]: 0.75 to 0.82) in the multivariable-adjusted model. The corresponding odds ratio was 0.78 (95% CI: 0.69 to 0.88) in the sibling and 0.72 (95% CI: 0.66 to 0.79) in the cousin comparison analysis. Conclusions: This nationwide, family-based study provides support for a protective effect of maternal smoking on offspring T1D. Mechanistic studies are needed to elucidate the underlying pathways behind this link.

Association between Smoking during Pregnancy and Short Root Anomaly in Offspring

Short root anomaly (SRA) is a dental anomaly with short dental roots and its pathogenesis is poorly understood. This study investigated the association between maternal smoking during pregnancy and SRA in offspring. A survey was conducted on 558 children aged 8–16 years from two public schools in Ulaanbaatar, Mongolia. SRA was diagnosed using cases with a root-crown ratio of maxillary central incisors of ≤1.0. A questionnaire survey was conducted to assess maternal lifestyle habits. Multiple logistic regression was used to analyse the association between maternal smoking during pregnancy and SRA in offspring after adjusting for possible confounders. The prevalence of SRA in these children was 14.2%. Children whose mothers smoked from pregnancy to date were found to be 4.95 times (95% confidence interval [CI]: 1.65–14.79) more likely to have SRA than those whose mothers never smoked, after adjusting for possible confounders. Additionally, children whose mothers had been exposed to passive smoking during pregnancy were found to be 1.86 times (95% CI: 1.02–3.40) more likely to have SRA than those whose mothers had not been exposed to passive smoke. Our population-based study suggests that maternal and passive smoking exposure during pregnancy can affect tooth root formation in children.

Maternal smoking status before and during pregnancy and bronchial asthma at 3 years of age: a prospective cohort study from the Japan Environment and Children's Study (JECS)

Background Maternal smoking exposure during pregnancy is an established risk factor for childhood asthma, but the association between maternal pre-pregnancy smoking status and asthma risk is not well understood. This study examined the association between maternal smoking status before and during pregnancy and bronchial asthma at 3 years of age. Methods The data of 75,411 mother-child pairs, excluding the missing data of exposure and outcomes from the Japan Environment and Children's Study (JECS) were used. The association between prenatal maternal smoking status and the risk of bronchial asthma at 3 years of age was determined using multivariate logistic regression analysis. Results The percentage of 3-year-old children with doctor-diagnosed bronchial asthma was 7.2%. The distribution of maternal smoking status before childbirth was as follows: Never = 60.0%, Quit before recognizing current pregnancy = 24.1%, Quit after finding out current pregnancy = 12.3%, and Still smoking = 3.6%. Maternal smoking during pregnancy was significantly associated with an increased risk of bronchial asthma at 3 years of age even after adjusting for pre- and postnatal covariates (adjusted odds ratio [aOR] 1.35, 95% confidence interval [CI] 1.16–1.57). Furthermore, mothers who quit before recognizing current pregnancy (aOR 1.10, 95% CI 1.02–1.18) or who quit after finding out about current pregnancy (aOR 1.11, 95% CI 1.01–1.23) were also significantly associated. Conclusions This study suggested that not only maternal smoking during pregnancy but also maternal smoking exposure of pre-pregnancy or early pregnancy may be associated with an increased risk of bronchial asthma in children.