A study published in JAMA Network Open finds that Danish women who had overweight or obesity body mass index (BMI) trajectories during childhood were less likely to have children as adults compared to those with average BMI trajectories, according to an Aug. 4 report.
Researchers analyzed data from 60,864 women born between 1950 and 1989 who attended school in Copenhagen. The study used annual school health records measuring height and weight from ages 6 to 15 years. Participants were grouped into five categories based on their childhood BMI: below-average, average, above-average, overweight, and obesity.
By linking this information with the Danish Medical Birth Register covering births from 1977 through 2022, the researchers found that across the study period, 78% of women gave birth while 22% remained childless. After adjusting for factors such as birth cohort and parental education level, the analysis showed that women with an overweight or obesity trajectory from as young as age six were less likely to give birth than those with an average BMI trajectory—particularly at older ages. For example, between ages 25 and 29 years, women with a childhood obesity trajectory were found to be 22% less likely to give birth; at ages 30–34 years they were found to be 42% less likely.
Dr. Pedersen said, "Although advancing age is a major driver of childlessness, with postponed parenthood being a substantial contributor, overweight and obesity appear to further increase these risks through physiological and social pathways, possibly including effects on egg quality and hormonal disturbances. So it is concerning that one in three school-aged girls in Europe are currently living with overweight or obesity."
Senior author Dr. Jennifer Baker from Copenhagen University Hospital – Bispebjerg and Frederiksberg said, "Our study paves the way for a better understanding of how overweight and obesity during childhood may contribute to involuntary childlessness. More broadly, our findings suggest that reproductive health has much earlier origins than is commonly appreciated. We need to be thinking of infertility as a cumulative physical and social experience... Recognizing these early-life influences could reshape how we understand reproductive health and identify opportunities to support it long before family planning begins."
The authors note their findings show associations but do not establish causality between childhood BMI trajectories and later-life childlessness. They also highlight limitations such as lack of adult BMI data for participants when trying to conceive and suggest further research is needed for broader generalizability.
