Shown is the percent of animals delivering versus day of pregnancy after various treatments: RU-486 (single treatment, 3mg s.c., on day 16,), daily treatments from day 13 until delivery for P4 (4 mg s.c. or 15 mg vaginal bid), 17P (10 mg s.c.) and controls (0.2 ml sesame oil (vehicle) s.c. or 0.18 ml vaginal gel bid). Note that injections of P4 completely blocked delivery, whereas 17P or vaginal P4 had no effect on delaying term delivery. RU- 486 induced preterm delivery.