Being overweight or obese during childhood can negatively impact a girl's fertility and reduce her likelihood of having children later in life, a recent study suggests. Researchers found that girls who gained the most weight from the age of six were less likely to become mothers by their mid-30s, with their chances diminished by as much as 42 percent.
The findings indicate that issues affecting reproductive health can begin at an earlier age than previously understood, highlighting the need for interventions to address a growing cause of involuntary childlessness. "Our findings suggest that less favourable BMI patterns from as young as six years old may increase a woman’s risk of childlessness from their mid-20s onwards," said lead author Dr. Dorthe Pedersen from Copenhagen University Hospital in Denmark. "By the time women reach their 30s, when many women start trying to conceive and fertility difficulties often become evident, the effects on reproductive capacity may already be established, underscoring the importance of preventive efforts focused on healthy growth and development in childhood."
In Western European countries, approximately 20 percent of women born around 1965 remain childless. Birth rates have fallen below replacement levels, and an estimated 5 percent of European women aged 18 to 40 do not intend to have children, suggesting that most childlessness is involuntary.
While a higher body mass index (BMI) in adult women is known to be associated with reduced reproductive capacity, research specifically examining the contribution of early-life BMI to adult childlessness and infertility has been limited. To investigate this, researchers analyzed data from 60,864 women born in Copenhagen between 1950 and 1989. Their height and weight were recorded annually during school health examinations. This data was linked with the Danish Medical Birth Register to identify girls who later gave birth between the ages of 18 and 45.
During the study period, 78 percent of the women gave birth, with an average age of 27. The remaining 22 percent remained childless. After accounting for factors such as relationship status, women with overweight or obese BMI trajectories starting from age six were less likely to give birth compared to those with a healthy childhood BMI trajectory, particularly at older ages.
Specifically, between ages 25 and 29, women with an obese childhood trajectory were 22 percent less likely to give birth than those with an average childhood BMI trajectory. This likelihood decreased further to 42 percent for women aged 30 to 34. Women with an overweight childhood trajectory were 9 percent less likely to give birth between ages 25 and 29 and 26 percent less likely between ages 30 and 34 compared to their peers with an average BMI trajectory.
Dr. Pedersen, whose findings were published in JAMA Network Open, noted that while advancing age is a significant factor in childlessness, overweight and obesity appear to exacerbate these risks through physiological and social mechanisms, potentially affecting egg quality and hormonal balance. She expressed concern that approximately one in three school-aged girls in Europe currently live with overweight or obesity.
Dr. Jennifer Baker, a senior author from Copenhagen University Hospital and president-elect of the European Association for the Study of Obesity, stated that the study enhances the understanding of how childhood overweight and obesity may contribute to involuntary childlessness. "More broadly, our findings suggest that reproductive health has much earlier origins than is commonly appreciated," she said. "We need to be thinking of infertility as a cumulative physical and social experience, with effects beginning many years before women wish to become pregnant. 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 acknowledged that their findings represent associations and do not establish a causal relationship between childhood BMI trajectories and childlessness. They also noted limitations, including the need for additional data on adult BMI to fully understand the impact of overweight and obesity during attempts to conceive.