The Impact of Vaginal and IM Progestins on the Cervix

Inclusion Criteria All Groups * Singleton gestation (16 0/7 - 23 6/7 weeks gestation) * Willing to provide informed consent * Age 18 - 50 years inclusive Additionally, Group 1: One or more prior term births (\>37 0/7 weeks); No prior spontaneous birth at 16 0/7 - 36 6/7 weeks; and normal cervical length (\>25 mm) Group 2: Cervical length of 20 mm or less at 16 0/7 - 23 6/7 weeks Groups 3 and 4: History of prior spontaneous birth at 16 0/7 - 34 0/7 weeks and normal cervical length (\> 25mm) at enrollment. Exclusion Criteria All Groups * Active labor * Active bleeding * On progestin therapy, chronic steroid, or current NSAID therapy * Actively receiving study treatment in another clinical trial (observational trials allowed) * Major fetal malformation lethal anomalies, or anomalies that may lead to early delivery or increased risk of neonatal death e.g., gastroschisis, spina bifida, or serious karyotypic abnormalities * Amniotic membranes prolapsed beyond the external os (ostium of uterus) or protruding into the vagina * Pregnancy without a viable fetus * Prenatal care or delivery planned elsewhere (unless the study visits can be made as scheduled and complete outcome information can be obtained) Additionally: Group 1: Cervical dilation greater than or equal to 3cm Group 2: Prior preterm birth (16 0/7 - 34 0/7); active deep vein thrombosis, pulmonary embolism, or history of these conditions; known liver dysfunction or disease (active hepatitis, HIV) Group 3: inabil…