- Patients who are pregnant or nursing. The effects of nivolumab on the developing human fetus are unknown. For this reason, women of child-bearing potential (WOCBP) must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. WOCBP must have a negative serum pregnancy test within 7 days of study enrollment, prior to dosing nivolumab, then every 6 weeks. After discontinuation from nivolumab these should be repeated at approximately 30 days and approximately 70 days. Women must not be breastfeeding.