In researcher it was found that for every 5-kg increase in body weight from age 18, there was a 5 percent increase in the current duration of pregnancy attempt. The adjusted median current duration was 0.5 months shorter for those who lost weight, 0.3 months longer for those who gained 4 to 19.9 kg, and 1.4 months longer for those who gained 20 kg or more, compared with women who maintained weight (P trend ≤ 0.001). For a 5-kg/m² increase in current BMI, the adjusted time ratio was 1.08. Being underweight at age 18 years correlated with longer current duration of pregnancy attempt compared with normal-weight women, after multivariable adjustment. No correlation with fecundity was seen for being overweight or obese at 18 years. Gaining weight in adulthood, being overweight or obese in adulthood, and being underweight at age 18 years were associated with a modest reduction in fecundity.