Objective: To investigate changes in menstrual cycle hormones and endo
metrial maturation that may contribute to the decline in fertility wit
h aging. Design: Prospective controlled clinical study. Setting: Norma
l human volunteers in an academic research institution. Subjects: Wome
n with regular menstrual cycles. Interventions: Thirty-two women, aged
20 to 30 or 40 to 50 years, had daily blood drawing starting on cycle
day 6 to 10 and continuing until 2 days after the onset of next mense
s. In addition, 60 women, aged 20 to 30 or 40 to 50 years, had a total
of 93 endometrial biopsies performed on day 7 to 9 after the LH surge
. Main Outcome Measures: Serum LH, FSH, E(2), inhibin, P, and placenta
l protein 14 (PP14) levels and histologic maturation of the endometriu
m. Results: Serum FSH levels were increased whereas inhibin concentrat
ions were reduced in the luteal-follicular transition of women >40 yea
rs. No other hormonal changes were seen in this population, including
P and PP14 secretion. Disruption of endometrial maturation occurred at
a similar frequency in both age groups. Conclusions: Follicular recru
itment, but not luteal function or endometrial maturation, is disturbe
d in cycling women >40 years and may contribute to the decline in fert
ility with aging.