OBJECTIVE: To generate estimates of the association between fecundability (probability of conceiving in a menstrual cycle) and urinary markers of ovarian aging, which are used in commercial fertility tests. OBJECTIVE: To generate estimates of the association between fecundability (probability of conceiving in a menstrual cycle) and urinary markers of ovarian aging, which are used in commercial fertility tests. DESIGN: Prospective time-to-pregnancy study. MATERIALS AND METHODS: Women, 30-44 years old, with no history of infertility, who had been trying to conceive for less than 3 months, provided early follicular phase serum and urine (N=99). They were followed until pregnancy or 6 months. While trying to conceive, women conducted standardized pregnancy testing and kept a diary to record bleeding and intercourse. Urine was analyzed for follicle stimulating hormone (FSH) and estrone 3-glucuronide (E1G); levels were creatinine-corrected. Cox models were used to calculate fecundability ratios. To adjust for patterns of intercourse, diary data were used to calculate day-specific probabilities of conception. RESULTS: Serum and urinary FSH were highly correlated (r=0.85, p<0.01) as were serum estradiol and urinary E1G (r=0.78, p<0.01). Urinary FSH and E1G were not strongly associated with fecundability. CONCLUSION: Serum and urinary measures of ovarian aging are highly correlated; however, urinary creatinine-corrected early follicular phase FSH and E1G are not strongly associated with natural fertility.