Body mass index at age 20 and subsequent childbearing: the Adventist Health Study-2

Some epidemiological, clinical, and laboratory studies suggest that underweight and obesity impact fertility.

This is cross-sectional study of 33,159 North American Adventist women, who were nulliparous at age 20 years and who, as a group, have a healthy lifestyle. Logistic regression analysis was used to assess how body mass index (BMI, kg/m(2)) at age 20 was related to never becoming pregnant, never giving birth to a living child, or not giving birth to a second or third child.

A total of 4954 (15%) of the women reported never becoming pregnant (nulligravidity) and 7461 (23%) women remained nulliparous. Underweight (BMI<18.5 kg/m(2)) at age 20 was associated with approximately 13% increased risk of nulligravidity or nulliparity. Women with BMI≥32.5 kg/m(2) when aged 20 had 2.5 (95% CI: 2.0, 3.1) times increased odds of nulliparity compared to women with BMI 20-24.9 kg/m(2). Increased risk was found for all groups of overweight women (BMI≥25 kg/m(2)). However, if the women gave birth to one live child after age 20, BMI≥32.5 kg/m(2) at age 20 had less impact (OR 1.6 [95% CI: 1.2, 2.2]) on the likelihood of not delivering a second child. In women who delivered two living children, obesity at age 20 had no bearing on the odds of having a third child.

Obesity and, to a lesser extent, underweight at age 20 increases the nulliparity rate. The results underscore the importance of a healthy weight in young women.