Childhood Overweight and Obesity Linked to Lower Childbirth Rates: Study

A large Danish cohort study of 60,864 women published in the JAMA Network Open found that those who were overweight or obese throughout childhood were less likely to have a child than women with an average childhood body mass index (BMI). The association became stronger with age, with women who had childhood obesity showing a 44% lower likelihood of childbirth at ages 35–45 years (HR 0.56). However, childhood BMI was not associated with overall infertility.

The population-based study tracked more than 60,000 women born in Copenhagen between 1950 and 1989, using measured height and weight records collected during school health examinations between the ages of 6 and 15 years. Among the 60,864 women included in the childbirth analysis, nearly 78% had their first child during the follow-up period, with a median age of 27.2 years.

Women whose BMI followed an obesity trajectory in childhood were significantly less likely to have their first child at younger reproductive ages when compared to women who maintained an average BMI trajectory. This difference became more pronounced as women aged. Between 25 and 29 years, women with childhood obesity had a 22% lower likelihood of giving birth, while between 35 and 45 years, they were 44% less likely to have had their first childbirth. Women with a childhood overweight trajectory showed a similar pattern, although the association was less pronounced.

Despite the delayed timing of childbirth, this study found no evidence that childhood BMI trajectories increased the risk of infertility. Among more than 58,000 women assessed for primary infertility and over 63,000 evaluated for any infertility diagnosis, childhood overweight and obesity were not associated with either outcome. The study noted that childbirth timing is influenced by multiple biological, social, and behavioral factors, and the observed association may reflect a combination of these influences rather than fertility alone.

The declining likelihood of childbirth at older reproductive ages among women with childhood obesity may become more significant as the natural fertility window narrows. Overall, the findings of this study suggest that promoting healthy growth during childhood could have lasting benefits beyond physical health, supporting reproductive well-being throughout adulthood.

Reference:

Pedersen, D. C., Aarestrup, J., Bjerregaard, L. G., Andersen, E. W., Jensen, A., Kjær, S. K., Juliusson, P. B., Rasmussen, K. M., & Baker, J. L. (2026). Early life BMI trajectories and associations with childbirth and infertility among women. JAMA Network Open, 9(8), e2626893. https://doi.org/10.1001/jamanetworkopen.2026.26893