Hello, Luckily, for the vast majority of women, sex right up until their due date is perfectly safe though it may become uncomfortable as the months pass. In some high-risk cases, however, sex during pregnancy can be risky. Many doctors recommend that women at risk for preterm labor avoid pregnancy sex because semen contains substances that can cause the uterus to contract. In your case twin pregnancy and cervical incompetence provoke preterm labour ,so better to avoid sex.