Sexual activity during weeks 29-36 of pregnancy does not increase women's risk of delivering preterm, according to a study of nearly 600 women who visited three prenatal clinics in North Carolina.1 By contrast, the results suggest that women who are sexually active late in pregnancy are considerably less likely than pregnant women who are not sexually active to deliver before 37 weeks of gestation.
As part of a larger study of preterm birth, researchers recruited women who were aged 16 or older and between 24 and 29 weeks pregnant from three community-based prenatal clinics in Chapel Hill and Raleigh. Between August 1995 and July 1998, researchers interviewed 1,853 women two weeks after recruiting them for the study, at approximately 28 weeks' gestation. In follow-up interviews before and after delivery, they asked women about their frequency of sexual intercourse, use of the male superior position, experience of orgasm and interest in intercourse, as well as the date of their most recent intercourse and whether they received any medical advice regarding bed rest.
The researchers assessed three measures of sexual activity during the 29-36-week gestational period: sexual intercourse during the last two weeks (any vs. none), time since last sexual intercourse (fewer than seven days vs. seven or more days ago) and orgasm within the past two weeks (any vs. none). Using conditional logistic regression models, the researchers calculated odds ratios measuring the association between sexual activity and preterm delivery, taking into account a range of demographic, reproductive and behavioral factors that may affect the risk of this outcome. The analyses included 187 women who delivered preterm and a control group consisting of 409 randomly selected women who were still carrying their pregnancies.
Women who attended the three clinics came from a range of social and economic backgrounds--though they generally were from lower- and lower-middle-class backgrounds--and from both urban and rural areas. The women who delivered preterm were similar to those in the control group in their demographic characteristics: About half of the women in each group were white, about a third in each group had completed high school and nearly half had education beyond high school. About equal proportions of women in each group were married (41% of women who delivered preterm and 45% of controls).
The women also were similar in their reports of the frequency of sexual intercourse before pregnancy (roughly 2.5 times per week) and during the first trimester (about twice weekly). For both groups of women, the frequency of sexual intercourse decreased as their pregnancies progressed. However, women who delivered preterm reported less-frequent sexual intercourse during their sixth month and, especially, in weeks 29-36 than did women with full-term pregnancies.
At the first interview, a smaller proportion of women who delivered preterm than of women in the comparison group reported having had at least one orgasm in the previous month (52% compared with 63%). This pattern was consistent through weeks 29-36. During weeks 29-36, a larger proportion of women who delivered preterm than of those in the comparison group reported reduced interest in sex in the last two weeks (71% compared with 57%). Furthermore, a larger proportion of women who delivered preterm than of women in the control group reported that a doctor or nurse had given them advice related to sexual activity during pregnancy (41% compared with 23%), including a recommendation that they stop or limit intercourse or orgasm (32% compared with 12%).
When women were asked why their frequency of intercourse decreased during weeks 29-36, a larger proportion of women who delivered preterm than of women in the control group reported medical reasons, such as receiving a recommendation of bed rest from their doctor, admission to the hospital or having surgery. In addition, women who delivered preterm were more likely than controls to say that they were in fair or poor health during late pregnancy (19% compared with 13%).
The regression analysis revealed no relationship between preterm delivery and women's frequency of sexual intercourse six months prior to pregnancy or during the first trimester. However, women who said during weeks 29-36 that they had had sexual intercourse in the past two weeks or fewer than seven days ago had reduced odds of delivering preterm (odds ratio, 0.3 for each measure); the odds of preterm delivery also were reduced if women had had an orgasm in the previous two weeks (0.4). Women who reported having had sexual intercourse but not an orgasm in late pregnancy and those who had not had intercourse but reported having had an orgasm late in pregnancy also had reduced odds of preterm delivery (odds ratio, 0.3 for each). These results did not change when the researchers controlled for demographic and socioeconomic variables.
The researchers also examined the association between sexual activity and preterm delivery among subgroups of women defined by marital status; diagnosis of bacterial vaginosis; and type of preterm delivery (preterm labor, premature rupture of membranes or medically induced preterm delivery). They also examined the association according to women's level of risk of preterm delivery, classifying women as "higher-risk" if they reported poor health during the 29-36-week period; had had a previous miscarriage, stillbirth or preterm birth; or had received medical advice regarding bed rest or limiting intercourse or orgasm during pregnancy.
For most subgroups, results of this analysis were similar to those for the overall cohort: Recent sexual activity was associated with significantly reduced odds of preterm delivery (odds ratios, 0.2-0.4). The most notable exceptions were that whereas sexual activity was associated with reduced odds of preterm delivery for married and higher-risk women, it was not associated with preterm delivery risk among women who were unmarried or at lower risk of this outcome. Odds ratios were lower for women who had medically induced deliveries than for those with other types of preterm delivery, and were comparable for women who had bacterial vaginosis and those who did not.
The researchers offer two possible interpretations of their findings. One is that the protective effect of sexual activity indicated by their data could be related to the amount of social support a pregnant woman experiences. The other is that the overall effect is partly attributable to higher-risk women's simply limiting or stopping late-pregnancy sexual activity. This interpretation, according to the researchers, is supported by the analysis for lower-risk women: Since these women had fewer medical reasons to reduce their sexual activity, the investigators note, they are a useful group in whom to assess "an effect of sexual activity per se," and no such effect was uncovered. The researchers conclude that "as a whole...continued sexual activity during late pregnancy was a strong predictor that a pregnancy [would] go full term."--B. Brown
REFERENCE
1. Sayle AE et al., Sexual activity during late pregnancy and risk of preterm delivery, Obstetrics and Gynecology, 2001, 97(2):283-289.