Childhood overweight linked to reduced fertility in women, study finds

A Danish study involving nearly 61,000 women reveals that excess weight from as early as age 6 may impact reproductive outcomes decades later, highlighting the importance of early weight management to support future fertility.

A large Danish cohort study suggests that excess weight in childhood may shape reproductive outcomes decades later, with girls whose body mass index stayed in the overweight or obesity range from as early as age 6 less likely to give birth as adults than peers who tracked at an average BMI. The association was already visible by the mid-20s and became more pronounced after age 30, according to the JAMA Network Open study of nearly 61,000 women. Public-health research has long shown that childhood obesity can carry consequences into adulthood, including later metabolic disease, so the new findings add another reason to treat early weight management as a life-course issue rather than a narrow paediatric one.

Jennifer Baker, head of research in lifecourse epidemiology at Copenhagen University Hospital, said the study points to lasting reproductive effects from elevated BMI in childhood and adolescence. She added that the absence of a clear link with diagnosed infertility may reflect Denmark’s fertility referral rules, which can limit access to IVF for women above certain BMI thresholds. In other words, some women with obesity may never enter the hospital infertility system, even if they go on to have difficulty conceiving or carrying a pregnancy. That makes childbirth data a more informative signal than infertility diagnoses alone.

The research does not prove that childhood obesity causes childlessness, but it fits with established biology. The American Society for Reproductive Medicine has said obesity in women is associated with ovulatory dysfunction, poorer response to fertility treatment, altered egg and uterine function and lower IVF birth rates, although most women with obesity remain fertile. The Danish authors also point to possible disruption of the hypothalamic-pituitary-ovarian axis and hormonal changes as plausible pathways. Baker stressed that the study does not show whether weight loss improves fertility, and she said counselling should stay aligned with current obesity and reproductive-health guidance.

For pharmacists and other clinicians, the practical lesson is timing. The conversation about weight, pregnancy and fertility may need to begin years before a patient is planning a family, especially because childhood overweight often persists into adult life. That makes person-centred counselling in paediatric, adolescent and family settings particularly important, alongside careful medication advice for people of reproductive age. Broader evidence also suggests that early-life obesity is tied to later health risks, reinforcing the value of prevention long before conception becomes an immediate concern.