Abdominal surgery (unrelated lu delivery) during pregnancy is not common. Review of a recent 17-year experience at our institution revealed 112 surgical procedures among 25.189 deliveries—an incidence of 0.44% (1 case for every 225 deliveries). Progestational agents have been used privphyiactically in such procedures, but few studies have adequately assessed the effectiveness of these drugs to prevent onset of premature labor. The present study involved 35 gravid patients who had been treated with various doses of hydroxy progesterone caproate before and after operations unrelated to delivery. These 35 patients were matched with 35 gravid control patients who had undergone similar operations but who had not received progestational compounds. Analysis revealed no significant difference in the abortion rate between these two groups.