New recommendations from the Center for Disease Control and Prevention says that women should wait at least 3 weeks after birth to restart oral contraceptives. During this time women are at an increased risk for blood clots and oral contraceptive use during this time adds to this risk .
The statement from the CDC explains:
Hematologic changes that occur normally during pregnancy, including an increase in coagulation factors and fibrinogen and a decrease in natural anticoagulants, result in an increased risk for VTE during the postpartum period. In addition, many postpartum women have additional risk factors that further increase their risk for VTE, such as age ≥35 years, smoking, or recent cesarean delivery. This is of concern when considering postpartum contraception options because combined hormonal contraceptives (i.e., those that contain both estrogen and progestin) are themselves associated with a small increased risk for VTE among healthy women of reproductive age.
Other safe methods birth control methods after birth include an IUD and condoms. Talk with your doctor about which method is correct for you.