TOPLINE

Women with overweight or obesity BMI trajectories during childhood were less likely to give birth in adulthood than those with average BMI trajectories. This association was more pronounced after 30 years of age. However, childhood BMI trajectories were not significantly associated with any infertility outcomes.

METHODOLOGY

• Researchers conducted a prospective population-based cohort study to evaluate associations between childhood BMI trajectories and later childbirth and infertility in women.
• They analyzed data from women born between 1950 and 1989, including 60,864 women in the childbirth analysis (median age at childbirth, 27.2 years), 58,148 in the primary infertility analysis (median age at diagnosis, 31.3 years), and 63,066 in the any infertility analysis (median age at diagnosis, 31.9 years). Participants were followed up for reproductive outcomes from January 1977 through December 2022.
• Childhood BMI was calculated from height and weight measurements collected during school health examinations from 6 to 15 years of age. Women were classified into five BMI trajectory groups — below-average, average, above-average, overweight, and obesity.
• Associations were assessed across four reproductive age groups — younger than 25, 25-29, 30-34, and 35-45 years — to examine patterns across the reproductive lifespan.
• The study combined data from multiple Danish national registries to identify childbirths and hospital-diagnosed cases of infertility.

TAKEAWAY

• After adjustments, women with obesity BMI trajectories in childhood were less likely to give birth as they aged than those with average BMI trajectories at 25-29 years of age (hazard ratio [HR], 0.78; 95% CI, 0.72-0.86), 30-34 years of age (HR, 0.58; 95% CI, 0.52-0.66), and 35-45 years of age (HR, 0.56; 95% CI, 0.46-0.67).
• Similarly, women with overweight BMI trajectories during childhood were also less likely to give birth as they aged than those with average BMI trajectories at 25-29 years of age (HR, 0.91; 95% CI, 0.86-0.96), 30-34 years of age (HR, 0.74; 95% CI, 0.69-0.79), and 35-45 years of age (HR, 0.82; 95% CI, 0.73-0.91).
• Women with above-average BMI trajectories during childhood showed similar childbirth patterns as those with average BMI trajectories at 18-24 and 25-29 years of age but were less likely to give birth at 30-34 years of age (HR, 0.91; 95% CI, 0.86-0.96) and 35-45 years of age (HR, 0.83; 95% CI, 0.76-0.91). No significant association with childbirth was observed among women with below-average BMI trajectories across any age group.
• Women with obesity BMI trajectories during childhood were less likely to be diagnosed with primary infertility at ages 20-45 years than those with average BMI trajectories (HR, 0.79; 95% CI, 0.68-0.92). No significant associations were observed between other childhood BMI trajectories and primary or any infertility.

IN PRACTICE

“By the time women reach their thirties, when fertility difficulties often become apparent, these effects may already be established, underscoring the need for preventive efforts focused on healthy growth and weight management well before the reproductive age,” the authors of the study wrote.

“Overall, these findings support the concept that reproductive health may be shaped long before reproductive age itself. Importantly, obesity should no longer be viewed solely as a pregnancy-related comorbidity, but rather a condition that influences the entire reproductive continuum, from conception to long-term offspring health,” experts wrote in an invited commentary accompanying the journal article.

SOURCE

The study was led by Dorthe C. Pedersen, PhD, Center for Clinical Research and Prevention, Copenhagen University Hospital-Bispebjerg and Frederiksberg, Copenhagen, Denmark. It was published online on August 4, 2026, in JAMA Network Open.

LIMITATIONS

Infertility may have been underidentified because women with lower educational attainment were less likely to seek medical care for fertility problems. The analysis lacked data on some potential confounding factors, leaving the possibility of residual or unmeasured confounding. The study did not capture BMI in adulthood, preventing the evaluation of the potential impact of weight during the reproductive years on childbirth and infertility.

DISCLOSURES

The study was funded by the Independent Research Fund Denmark. One author disclosed receiving grants from the funding source during the conduct of the study and consulting fees from industry, with all fees paid to the author’s institute outside the submitted work.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.