A prospective study of early pregnancy loss.

The New York State Early Pregnancy Detection Study was a prospective study of early pregnancy loss, between implantation and menses, in 217 women attempting to become pregnant during 1989-1992. Women collected urine samples on three consecutive mornings during the late luteal phase of their menstrual cycle, for up to 12 cycles, contributing samples for 1253 menstrual cycles. Urinary human chorionic gonadotrophin (HCG), measured using an immunoradiometric assay, was the biomarker for pregnancy. We observed a range of early pregnancy loss (EPL) rates, from a low estimate of 11.0% to a high estimate of 26.9%, depending on the definition used and the subgroup analysed. Based on a definition of 3 days of HCG concentration > or = 4.00 pmol/l, 2 days > or = 5.33 pmol/l or the last day of HCG > or = 6.67 pmol/l, we identified 115 positive cycles; 95 cycles were clinically confirmed pregnancies and 20 cycles were EPL, giving an EPL rate of 17.4% [95% confidence interval (CI) 11.0-25.6]. In addition, we observed an EPL rate of 19.5% (95% CI 11.3-30.1) for samples collected within a 15 day window around menses, and a rate of 20.3% (95% CI 11.3-32.2) for samples limited to the first three menstrual cycles. Because studies use urine collection schemes other than daily sampling, the definition of pregnancy will be crucial in defining EPL.