Girls who are overweight or obese in childhood face a significantly reduced likelihood of becoming mothers later in life, according to a recent study.
The research indicates that weight gain from as early as six years old can dramatically lower a girl's fertility, with those accumulating the most weight having up to a 42% lower chance of having a family by their mid-30s.
These findings suggest that issues with reproductive health can begin much earlier than previously understood and highlight the need for interventions to address a growing cause of involuntary childlessness. Lead author Dr. Dorthe Pedersen of Copenhagen University Hospital stated that unfavorable Body Mass Index (BMI) patterns starting at age six may elevate a woman's risk of childlessness from her mid-20s onward.
By the time women reach their 30s, when many attempt to conceive and fertility difficulties become apparent, the impact on reproductive capacity may have already been established. This underscores the importance of preventive measures focused on healthy growth and development during childhood, Pedersen added.
In Western European countries, approximately 20% of women born around 1965 remain childless, with birth rates falling below replacement levels. While only about 5% of European women aged 18 to 40 intend to remain childless, suggesting that most childlessness is involuntary, the connection between early-life BMI and adult infertility is becoming clearer.
To investigate this link, researchers analyzed data from 60,864 women born in Copenhagen between 1950 and 1989. Height and weight measurements were collected annually during school health examinations. The study identified women who gave birth between the ages of 18 and 45 by cross-referencing with the Danish Medical Birth Register.
Over the study period, 78% of the women gave birth, with an average age of 27, while 22% remained childless. After accounting for factors like relationship status, women with an overweight or obese trajectory from age six were less likely to give birth compared to those with a healthy childhood BMI trajectory.
Specifically, between ages 25 and 29, women with an obese childhood trajectory were 22% less likely to give birth, and this figure rose to 42% less likely between ages 30 and 34. For women with an overweight childhood trajectory, the likelihood of giving birth decreased by 9% between ages 25 and 29, and by 26% between ages 30 and 34.
Dr. Pedersen noted that while advanced age is a primary driver of childlessness due to postponed parenthood, being overweight or obese appears to amplify these risks through physiological and social pathways, potentially affecting egg quality and hormonal balance. The observation that one in three school-aged girls in Europe currently live with overweight or obesity is a cause for concern.
Senior author Dr. Jennifer Baker, also from Copenhagen University Hospital, stated that the study enhances the understanding of how childhood overweight and obesity may contribute to involuntary childlessness. The findings suggest that reproductive health originates much earlier than commonly recognized, and infertility should be viewed as a cumulative physical and social experience beginning years before family planning.
Recognizing these early-life influences could reshape the understanding of reproductive health and identify opportunities for support long before individuals plan to have children. The authors acknowledge that these findings represent associations and do not establish a causal relationship, noting the need for further data on adult BMI to fully understand the impact of overweight and obesity during conception attempts.