Is there a seasonal pattern in risk of early pregnancy loss?
We recruited 221 women with no known fertility problems who were discontinuing contraception to conceive a pregnancy. The primary objective of this prospective study was to estimate the incidence of very early pregnancy loss by using a highly sensitive and specific assay to detect the pregnancy hormone chorionic gonadotropin in first morning urine specimens. We found the risk of early pregnancy loss, defined as loss within 6 weeks of the last menstrual period, to vary by season of conception, with a large amplitude and some consistency across the 3 years of the study. Such a seasonal pattern may reflect the contribution of an environmental factor that varies with season. The peaks in risk ranged from early September to early December. A seasonal pattern of early pregnancy loss should contribute to a corresponding lagged seasonal pattern in livebirths. Accordingly, we looked for corroborative evidence in regional birth data from the same years. There was some correspondence, but this wa
