Preconception and Early-Pregnancy Body Mass Index in Women and Men, Time to Pregnancy, and Risk of Miscarriage.
Level 3 - non-randomized controlled study
Prospective cohort study
PubMed 39298166 · doi:10.1001/jamanetworkopen.2024.36157
What was done
A prospective population-based cohort study in Rotterdam, Netherlands, followed 3,604 women and their partners from preconception or early pregnancy through birth (August 2017 to July 2021). The study examined associations between maternal and paternal body mass index (BMI) and reproductive outcomes: fecundability (monthly probability of conceiving), subfertility (time to pregnancy >12 months or assisted reproductive technology use), and miscarriage (<22 weeks gestation), assessed via questionnaires and clinical records.
What was found
Each 1-unit increase in BMI decreased fecundability in women (fecundability ratio [FR] 0.98, 95% CI 0.97–0.99; n=3,033) and men (FR 0.99, 95% CI 0.98–1.00; n=2,288). Relative to normal weight, female overweight (FR 0.88, 95% CI 0.80–0.98) and obesity (FR 0.72, 95% CI 0.63–0.82) reduced fecundability. Subfertility odds in women were elevated for underweight (OR 1.88, 95% CI 1.22–2.88), overweight (OR 1.35, 95% CI 1.11–1.63), and obesity (OR 1.67, 95% CI 1.30–2.13). Male obesity also increased odds of subfertility (OR 1.69, 95% CI 1.24–2.31). Overweight (OR 1.49, 95% CI 1.12–1.98) and obesity (OR 1.44, 95% CI 1.00–2.08) in women were associated with increased odds of miscarriage (n=2,770).
Why it matters
These findings show that abnormal BMI in both partners—not just maternal weight—is linked to longer time to pregnancy and increased subfertility, underscoring the importance of couple-centered preconception health.
Limits
As an observational cohort, residual confounding from unmeasured lifestyle, dietary, or metabolic factors cannot be ruled out. BMI was captured either preconception or during early pregnancy rather than at a single standardized time point. The cohort was conducted in a single metropolitan area in the Netherlands, which may limit generalizability to other geographic or ethnic populations.
Cited by
- supports Being either significantly underweight or significantly overweight reduces a woman's likelihood of getting pregnant.