BMI as a modifying factor in the relations between age at menarche, menstrual cycle characteristics, and risk of preeclampsia.

To examine the relations between age at menarche and menstrual cycle characteristics and preeclampsia risk, we analyzed data from a case-control study conducted from 1998 to 2002. Usual menstrual cycle characteristics among 286 preeclampsia cases and 471 normotensive controls were assessed using a structured interview during postpartum hospitalization. We used multivariable logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI), adjusting for confounders. We also examined the influence of pre-pregnancy body mass index (BMI) on selected hypothesized relations. Among lean women (pre-pregnancy BMI < 25 kg/m(2)), preeclampsia risk was lower in those reporting cycles > or = 36 days in length (adjusted OR 0.78, CI 0.35-1.83) and menarche at > or = 14 years (adjusted OR 0.48, 95% CI 0.28-0.82). In contrast, among overweight or obese women, preeclampsia risk was higher in those with long cycles (OR 3.11, 95% CI 0.62-1.56, p(interaction) = 0.16) and late menarche (OR 1.53, 95% CI 0.59-3.97, p(interaction) = 0.03). These data suggest that adiposity influences the relations between usual menstrual cycle length, age at menarche, and preeclampsia. Overweight women with long cycles are at particularly high preeclampsia risk.