Follicular phase hormone levels and menstrual bleeding status in the approach to menopause

OBJECTIVE: (1) Characterize the relationship between follicular phase hormone levels and menstrual bleeding patterns in the approach to menopause; (2) identify racial differences in hormone levels; (3) determine independent contributions of menstrual status, race, age, BMI, and smoking to hormone levels. DESIGN: Randomly identified, population-based cohort, stratified to obtain equal numbers of African American and Caucasian women, prospectively followed for 5 years. SETTING: Women in Philadelphia County, PA, identified by random-digit telephone dialing. PARTICIPANT(S): Women aged 35 to 47 years with regular menstrual cycles at enrollment (N = 436). DATA COLLECTION: Blood sampling twice in each of 7 assessment periods during days 1-6 of the cycle, menstrual dates identified through structured interview and daily symptom reports, anthropometric measures and standardized questionnaires at each assessment period. MAIN OUTCOME MEASURE(S): Serum levels of follicular E(2), FSH, inhibin B, and LH. RESULT(S): The mean levels of E(2), FSH, inhibin B, and LH were differentially associated with the 5 menstrual status groups defined by changes in bleeding patterns. Significant changes in hormone levels occurred prior to missed menstrual cycles for inhibin B, FSH, and LH. All hormones had a highly significant interaction between menstrual status and BMI. African American women had significantly lower levels of E(2) and LH compared to Caucasian women in univariate analyses. The interaction of race, menstrual status, and BMI was highly significant (P<.001) for E(2), with African American women having lower E(2) levels until postmenopause, when E(2) levels were higher in AA women with BMI > or =25 and BMI > or =30. CONCLUSION(S): Levels of E(2), FSH, LH, and inhibin B are significantly associated with menstrual bleeding patterns in late reproductive age women and differentiate the earliest stages of the menopausal transition. Racial differences in mean levels of E(2) appear strongly mediated by BMI.