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, folli cle 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 ch aracteristics between groups. High BMI was significantly associated with yo unger age at menarche and less sleeping time. No differences were observed between high- and low-BMI groups in cycle length or diameter of the dominan t follicle. Luteinizing hormone levels were significantly higher only in th e beginning of the cycle in women with low BMIs than in those with high BMI s. Follicle-stimulating hormone levels were also significantly higher but w ere high during all three phases of the cycle (early follicular, periovulat ory, and luteal phases). Mean levels were approximately 1.9, 1.8, and 1.2 t imes 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-stimul ating hormone levels and BMI were inversely associated during the whole cyc le, independent of age. (Obstet Gynecol 2000;96:8-12. (C) 2000 by The Ameri can College of Obstetricians and Gynecologists.).