The association of sexual intercourse during pregnancy with labor onset.

Background: Pregnancy is one of the most critical periods in women's lives. Sexual relationships change in this period. Monitoring of uterine contractions has been shown increase in uterine activity after sexual intercourse in pregnant women.

Objectives: This study aimed to determine the association of sexual intercourse during pregnancy with labor onset.

Patients and methods: This cross-sectional study included 120 pregnant women with signs of labor onset at referral hospitals of Kashan University of Medical Sciences between November and March 2012. Signs of labor onset included labor pain, bloody show, or rupture of membrane. Subjects were investigated in two groups regarding history of coitus in the last week of pregnancy. A questionnaire containing demographic questions, obstetrical history, and sexual activity was completed by trained midwife through face-to-face interview. Chi-square test, Fisher's exact test, and t-test were used to check the homogeneity of the two groups for basic and confounding variables. Independent-samples t-test was used to compare differences between groups in terms of mean gestational age.

Results: There was no significant difference between groups in age (P = 0.434), body mass index (P = 0.705), neonatal weight (P = 0.421), maternal education (P = 0.963), occupation (P = 0.381), and parity (P = 0.925). Gestational age at the time of delivery was significantly lower in intercourse group in comparison with control group based on last menstrual period (P = 0.012) and ultrasonography (P = 0.002). There was no correlation between intercourse and cause of admission (P = 0.720). Type of delivery (cesarean section or vaginal delivery) was not affected by intercourse (P = 0.820) or contact with semen (P = 0.841). Results showed no significant difference in neonatal weight based on presence of sexual intercourse (P = 0.422) or contact with semen (P = 0.583) at the last week of pregnancy.

Conclusions: Sexual activity in last week of pregnancy might be associated with the onset of labor. Therefore, in the absence of complications in term pregnancy, sexual activity can be considered as a natural way to prevent post term pregnancy.