Role of 200 mg Versus 400mg Vaginal Progesterone in Prevention of Preterm Labor in Twin Gestation

Inclusion Criteria: * Women pregnant in dichorionic twins. * Transvaginal sonographic cervical length is \<25 mm at 18-22 weeks gestational age. * No symptoms, signs or other risk factors for preterm labor. Exclusion Criteria: * Known allergy or contraindication (relative or absolute) to progesterone therapy. * Monochorionic twins. * Known major fetal structural or chromosomal abnormality. * Intrauterine death of one fetus or death of both fetuses. * Fetal reduction in the current pregnancy. * Cervical cerclage in the current pregnancy. * Medical conditions that may lead to preterm delivery. * Rupture of membranes. * Vaginal bleeding.