Objective: To evaluate gonadotropins, estrogen, and insulin-like growth hormone factor (IGF)-I and its binding proteins throughout the normal menstrual cycle and during aging within the reproductive life span.
Design: Daily blood samples were obtained from 17 normally cycling women.
Setting: Center for Fertility and Reproductive Medicine, Newark, New Jersey.
Participants: Ten women aged 19 to 34 years old and seven women aged 42 to 47 years old.
Main outcome measures: Luteinizing hormone (LH), FSH, E2, and P were assayed in daily blood samples. Early follicular, late follicular, midluteal phase, and samples taken at ovulation were also assayed for IGF-I and IGFBP-I and IGFBP-III.
Results: Follicle-stimulating hormone (FSH) increased significantly with reproductive aging. IGF-I and its binding proteins did not fluctuate through the menstrual cycle. IGF-I and its binding proteins did not change over the 28-year time span studied, in the face of significantly increased circulating estradiol associated with reproductive aging.
Conclusion: Rising E2 may be a subtle harbinger of the perimenopause. IGF-I and its binding proteins did not decrease with cycle stage or with aging during the reproductive years, perhaps because of increased estradiol stimulation of the somatotrophic axis.