Effect of coitus on recurrent preterm birth.

OBJECTIVE: To estimate the impact of sexual behavior on the risk of recurrent spontaneous preterm birth at less than 37 weeks of gestation.

METHODS: This is a secondary analysis of a multicenter, blinded observational study of endovaginal sonographic examinations performed at 16-18 weeks of gestation on 187 women with singleton gestations who were at high risk for recurrent spontaneous preterm birth (prior spontaneous preterm birth at < 32 weeks of gestation). At the time of enrollment, each woman was interviewed by a research nurse with regard to her sexual history. The patient was asked about the number of sexual partners in her lifetime, the number of sexual partners since the start of her pregnancy, and, on average, the frequency of intercourse per week in the preceding month.

RESULTS: A total of 165 pregnancies were available for this analysis. The population incidence of spontaneous preterm birth at less than 37 weeks of gestation in the study pregnancy was 36%. An increasing number of sexual partners in a woman's lifetime was associated with an increased risk of spontaneous preterm delivery (one partner 19%, 2-3 partners 29%, >or= 4 partners 44%, P = .007), whereas the number of sexual partners since the start of pregnancy was not (P = .42). Women who reported infrequent sexual intercourse during early pregnancy had an incidence of recurrent spontaneous preterm birth of 28% compared with 38% in those women who reported some intercourse (P = .35).

CONCLUSION: Self-reported coitus during early pregnancy was not associated with an increased risk of recurrent preterm delivery. There was an association between increasing number of sexual partners in a woman's lifetime and recurrent preterm delivery.

LEVEL OF EVIDENCE: II-2.