Obesity among women of childbearing age has increased globally, and maternal obesity during pregnancy has been linked to a range of adverse pregnancy outcomes and offspring health problems. Evidence on whether maternal body mass index (BMI) in early pregnancy predicts long-term offspring mortality remains limited. This nationwide cohort study from Sweden examined associations between maternal BMI in early pregnancy and offspring all-cause and cause-specific mortality from birth up to early adulthood.
The study included 2,606,684 live births recorded in Swedish national registers for 1982–2014 (with 1990 and 1991 excluded). Maternal BMI in early pregnancy was obtained from the Medical Birth Register and categorized as: underweight (<18.5 kg/m2), normal weight (18.5–24.9 kg/m2), overweight (25.0–29.9 kg/m2), obesity grade I (30.0–34.9 kg/m2), obesity grade II (35.0–39.9 kg/m2), and obesity grade III (≥40.0 kg/m2). Offspring deaths and underlying causes were ascertained from the national Cause of Death Register. Follow-up continued from birth until death, emigration, or December 31, 2023, whichever occurred first; the median follow-up was 22.4 years (IQR 14.9–30.7 years).
The primary analysis used Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) for offspring mortality per 1 unit increase in maternal BMI and across BMI categories, with normal BMI as the reference. Models adjusted for maternal characteristics recorded at childbirth: age, education, income, marital status, country of birth, smoking status in early pregnancy, and a history of psychiatric disorders or cardiovascular disease before the childbirth. The investigators also implemented a cousin comparison analysis to assess potential confounding by shared familial (genetic or environmental) factors. The role of adverse pregnancy outcomes such as preterm birth and hypertensive disorders was examined in stratified or adjusted analyses where reported.
During the study period 21,981 offspring (0.8% of the cohort) died. Maternal BMI showed a positive association with offspring all-cause mortality. As a continuous measure, each 1 kg/m2 increase in maternal BMI was associated with HR 1.03 for offspring mortality (95% CI 1.02–1.03; p < 0.001). Compared with offspring of mothers with normal early-pregnancy BMI, offspring of mothers who were overweight or obese had higher risks of premature death. Reported category-specific HRs were:
These results indicate a graded, dose–response relationship between higher maternal BMI and greater offspring all-cause mortality risk.
The study reported that similar positive associations were observed for several common causes of death in young people, notably respiratory diseases, cardiovascular diseases, and congenital anomalies. The main text emphasizes that the associations persisted across multiple cause-specific endpoints, consistent with a broad pattern rather than being confined to a single cause category.
To evaluate the influence of familial confounding, the investigators conducted a cousin comparison analysis. In these within-family analyses, associations of maternal BMI with offspring mortality were attenuated compared with population-level estimates but remained present. This attenuation suggests that shared familial factors (genetic or environmental) explain part, but not all, of the observed associations. The authors also examined how adverse pregnancy outcomes related to the associations; details on the extent of mediation or modification by specific pregnancy complications are presented in the full report.
The authors note several important limitations. Residual confounding cannot be excluded despite adjustment for measured maternal characteristics and the use of cousin comparisons. The observational design prevents causal inference; the reported associations should not be interpreted as evidence that higher maternal BMI causes offspring mortality. Data come from Swedish national registers, and certain variables or unmeasured confounders may not have been available or fully accounted for.
In this large nationwide cohort, higher maternal BMI in early pregnancy was associated with an increased risk of offspring death up to early adulthood, with a graded increase in risk by obesity category and consistent patterns across several causes of death. The findings persisted, though were attenuated, in cousin comparison analyses, indicating partial confounding by familial factors. The authors conclude that, given rising obesity prevalence among women of childbearing age, further research is needed to understand mechanisms linking maternal adiposity to long-term offspring mortality. If replicated, these results support public health efforts to promote a healthy maternal BMI prior to conception as a potential strategy to improve long-term child health.
Notes: The study period, sample size, BMI categories, hazard ratios, confidence intervals, follow-up duration, and analytic methods reported here are drawn directly from the published article. The authors caution against interpreting these associations as causal.