The timing for starting combination OCs after pregnancy varies: After a 1st-trimester spontaneous or induced abortion: Started immediately For deliveries at 12 to 28 weeks gestation: Started within 1 week if women have no other significant risk factors for thromboembolism After a delivery at > 28 weeks: Not started until > 21 days postpartum because risk of thromboembolism is additionally increased during the postpartum period (however, should be delayed 42 days if women are exclusively breastfeeding [feeding on demand including night feedings and not supplementing with other foods] or if their risk of venous thromboembolism is increased [eg, because of a recent cesarean delivery] In 98% of women who are exclusively breastfeeding and in whom menses does not resume, pregnancy does not occur for 6 months postpartum even when no contraception is used.