May 9, 2002 -- It's been thought that the timing of sex -- waiting too long after ovulation -- can cause birth defects. However, a new study finds no link between aging gametes (egg and sperm) and major birth defects like Down syndrome.
"Overall, our findings are reassuring for users of natural family planning, for couples who have intercourse episodically, or for couples who have intercourse infrequently of their own volition for health or other reasons," writes Joe Leigh Simpson, MD, an obstetrics/gynecology researcher with Baylor College of Medicine in Houston.
His study appears in this week's issue of The Lancet.
In their study, Simpson and colleagues reviewed records of over 600 infants born to women who had recorded timing (with regard to presumed ovulation) of sexual intercourse leading to conception. These were all women attending family planning clinics in South America, Europe, and the U.S.
"Optimally timed conceptions" were defined as those occurring on the day -- or one day before -- ovulation because the egg and sperm were unlikely to have been retained in the woman's genital tract for "prolonged" periods, Simpson writes.
All others were regarded as "non-optimal conception," whether the sperm was in the uterus more than two days before ovulation and fertilization -- or if sperm met egg one day or more after ovulation.
"Major anomalies" were defined as those causing death, severe handicap, or structural malformations requiring surgery.
There was only a miniscule difference in the number of babies born with major anomalies or Down syndrome from optimally timed conceptions (2.5% and 0.5%, respectively), compared with babies born from non-optimally timed conceptions (2.7% and 0.7%, respectively).
"There is no association between aging gametes and major birth defects, including Down syndrome," Simpson writes.
His findings regarding Down syndrome are consistent with other recent studies, he says.