Belimumab (Benlysta) in Pregnancy There has been no study to determine the safety of Belimumab in pregnant women. It may cross the placenta and become injurious for the fetus. It is preferred to stay cautious. Belimumab is registered in the pregnancy registry for drugs.The number for the registry is 1-877-681-6296. Belimumab (Benlysta) in Nursing Mothers There has been no study to determine the safety of Belimumab in nursing mothers. Since antibodies pass into breast milk therefore, Belimumab is not recommended for use among nursing mothers.