Gonadotropin and body mass index: High FSH levels in lean, normally cycling women

Objective: To characterize the relationships between body mass index (BMI) and LH or FSH levels over the cycle in normally cycling women. Methods: We compared baseline characteristics, cycle characteristics, follicle sizes, and daily hormone levels among women with low (n = 22), normal (n = 63), or high (n = 22) BMIs over 326 cycles. Results: There were no significant differences in age or other lifestyle characteristics between groups. High BMI was significantly associated with younger age at menarche and less sleeping time. No differences were observed between high- and low-BMI groups in cycle length or diameter of the dominant follicle. Luteinizing hormone levels were significantly higher only in the beginning of the cycle in women with low BMIs than in those with high BMIs. Follicle-stimulating hormone levels were also significantly higher but were high during all three phases of the cycle (early follicular, periovulatory, and luteal phases). Mean levels were approximately 1.9, 1.8, and 1.2 times higher, respectively, in the low-BMI group than the high-BMI group. Conclusion: Luteinizing hormone levels and BMI were inversely associated in normally cycling women during the early follicular phase. Follicule-stimulating hormone levels and BMI were inversely associated during the whole cycle, independent of age. (Obstet Gynecol 2000;96:8-12. (C) 2000 by The American College of Obstetricians and Gynecologists.).