Algorithm for Consideration of the Use of Progestins for Reducing the Risk of Preterm Birth (PTB). Aif Transvaginal Ultrasound (TVU) Cervical Length (Cl) Screening is Performed. B17- Hydroxyprogesterone Caproate (17-P) 250 mg Intramuscularly Every Week from 16-20 to 36 Weeks, if Selected Weighing the Risk and Benefits of Research to Late Discussed on the Prior Page. Cfor Example, Daily 200-mg Suppository or 90-mg Gel from Time of Diagnosis of Short Cl to 36 Weeks i