Petridou's comprehensive study 1 of triggers for preterm delivery analyses socio-demographic, lifestyle and pregnancy rated variables. They showed that women who delivered at 33–35 weeks of gestation were twice as likely to have had intercourse in the last two weeks of their pregnancy compared with women who delivered just before 37 weeks. The odds ratio increased to 3.2 for deliveries before the 33rd week of gestation. They conclude that coitus should be discouraged as it appears to be a risk factor for preterm delivery. Perhaps there is a simpler and more logical explanation. Women with a term uterus are far less likely to have sex compared with women with a smaller preterm uterus.
It might be wrong to conclude that sexual intercourse precipitates preterm labour. It might be more appropriate to conclude that women are more likely to have intercourse before term for other natural and understandable reasons.