APPLICATION OF A METHOD FOR ESTIMATING DAY OF OVULATION USING URINARYESTROGEN AND PROGESTERONE METABOLITES

Longitudinal epidemiologic studies of menstrual and reproductive funct ion are more informative if one can identify day of ovulation. We prev iously developed a method for estimating day of ovulation that is feas ible for epidemiologic studies. The method relies on the relative conc entrations of estrogen and progesterone metabolites in daily first-mor ning urine specimens and does not require creatinine adjustment. This paper describes results of applying this method to a large study with 724 menstrual cycles from 217 women. The method estimated a credible d ay of ovulation in 88% of cycles. Missing data accounted for most of t he failures. When we excluded anovulatory cycles (1%) and cycles with missing data, the method estimated a day of ovulation in 97% of cycles . Variance in luteal phase length was small for our sample, suggesting that this method of identifying a day of ovulation introduces no more measurement error than when day of ovulation is determined by plasma luteinizing hormone (LH), the standard clinical method.