IS THERE A SEASONAL PATTERN IN RISK OF EARLY-PREGNANCY LOSS

We recruited 221 women with no known fertility problems who were disco ntinuing 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 detec t 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 conc eption, with a large amplitude and some consistency across the 3 years of the study. Such a seasonal pattern may reflect the contribution of an environ mental factor that varies with season. The peaks in risk r anged from early September to early December. A seasonal pattern of ea rly pregnancy loss should contribute to a corresponding lagged seasona l pattern in livebirths. Accordingly, we looked for corroborative evid ence in regional birth data from the same years. There was some corres pondence, but this was largely limited to the first: year of the study .