During the past years there has been a conflict between different studies regarding the correlation between intercourse during pregnancy and early labor. Brustman et al showed that women that were at a high risk for early delivery and had intercourse and then an early labor had significantly increase uterine activity compared to women at low risk. Petridou et al showed that this risk is significantly higher at week 33 of gestation. However, the Cochrane Library summary leaves the question of correlation between intercourse and early labor unanswered. In Sayle et al's study showed no correlation between early delivery and intercourse. In 2004 Oguma described 3 polymorphisms in the Prostanoid receptor gene. These polymorphisms were correlated to increased activity of smooth muscles of bronchi in asthma. Since this gene is also expressed in the uterine muscles we wanted to determine whether there is a correlation between the three polymorphisms T-549C, C-441T, T-197C, G+1044A and early delivery due to intercourse.