Biologics
Antibodies are an interesting lot, Dr. Murase noted. Maternal antibodies are transported to the fetus across the villi by Fc receptor; most of this transfer happens during the third trimester. The large, hydrophilic monoclonal antibodies infliximab, adalimumab, and ustekinumab travel this way as well. Cord blood can contain 50% higher serum levels than in maternal blood. Etanercept, however, is a fusion protein that diffuses across the placenta. Cord blood levels generally exceed maternal levels by less than 7%.
There is one published report of a fetal death associated with maternal infliximab for Crohn’s disease. The infant was healthy until it received a Bacillus Calmette–Guerin vaccine. It then developed widespread eczematous dermatitis, head lag, and poor weight gain and died at 4.5 months.
“This is another important counseling point,” Dr. Murase said. “Babies who have been exposed to infliximab in utero can’t have that vaccination in the first 9 months of life.”
Perhaps the safest bet for a pregnant women who needs a biologic is PEGylated certolizumab. “Certolizumab is the only PEGylated anti-TNF [tumor necrosis factor] without an Fc region; study of patients greater than 30 weeks pregnant certolizumab levels were below 0.032 mcg/mL in 13 of 14 infant samples at birth.”