Lancet 05/09/2002 By Harvey McConnell
There is no clinical evidence supporting the widespread assumption that sexual intercourse too soon or too long after ovulation is associated with an increased risk of birth defects and Down’s syndrome. This has been shown in a four nation study by Dr Joe Simpson and colleagues at the Department of Obstetrics and Gynaecology, Baylor College of Medicine, Houston, Texas, United States. The investigators point out that it is not know if prolonged retention of gametes in the female reproductive tract before fertilisation –aging sperm or oocyte– compromises embryonic development, specifically causing chromosomal aneuploidy There has been circumstantial evidence but no studies have assessed the specific effects of conception timing on pregnancy outcome.
Study participants were women using natural family planning who became pregnant either inadvertently or deliberately, enrolled at natural family planning centers in Santiago, Chile; Bogota and Medellin, Colombia; Milan, Italy; and Washington, DC.
The natural family planning method used by 93 percent of the women was the ovulation method: the last day at which lubrication or stretchable mucus is present on the vulva is taken to be the date of ovulation. Conceptions resulting from intercourse on the day before or the day of presumed ovulation (day -1 or 0) were regarded as “optimal” because gametes are unlikely to have undergone prolonged retention in the genital tract before fertilisation. All other conceptions were regarded as “non-optimal”, whether due to conceptions in the preovulatory phase (sperm two or more days old before ovulation and fertilisation) or in the postovulatory phase (ova aged one day or more after ovulation).
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