Objectives: We describe the epidemiologic characteristics of conception, including subclinical early pregnancy loss, in a population of healthy women volunteers who had heterogeneous fertility experiences, and we describe the conception experience of women within this group who had evidence of impaired fertility.
Study design: This was a prospective observational study of a cohort of women employed in two semiconductor manufacturing facilities. A total of 148 volunteers completed interviews and daily diaries and collected daily urine specimens for an average of 7 months. Conception, including subclinical losses and clinical pregnancies, was determined with a highly sensitive and specific assay for urinary human chorionic gonadotropin, and ovulation was determined with assays of urinary ovarian steroid hormones.
Results: There were 679 menstrual cycles at risk for pregnancy contributed by 124 (84%) of the 148 women. Women with evidence of subfertility before or during the study period had a rate of early pregnancy loss of 70% compared with 21% in women without fertility problems (relative risk 2.6, 95% confidence interval 1.8 to 3.8). The risk of pregnancy loss associated with subfertility increased with age and remained the same in women treated with clomiphene citrate.
Conclusions: These results suggest that subfertile women have increased subclinical pregnancy losses regardless of fertility treatment and that the association between reduced fertility and advancing age may be related, in part, to early subclinical pregnancy loss.