The capacity of prenatal stress to disrupt the placental transfer of maternal antibody was evaluated in neonatal squirrel monkeys (Saimiri boliviensis peruviensis) gestated under different pregnancy conditions. Normal squirrel monkey offspring (n= 63) were compared with infants generated from pregnancies that involved either a single or 3 periods of disturbance (ns= 21 and 29, respectively). At parturition, levels of antibody (IgG) were determined in mothers and neonates. Only the chronic disturbance condition significantly altered antibody levels in the mothers, resulting in lower IgG. Antibody transfer to the fetus was also affected only by chronic disturbance. In this case the effect was bidirectional, influenced by the sex of the infant. Males were born with lower levels, whereas female infants actually had higher-than-normal IgG, despite lower titers in their mothers. Because virtually all IgG is derived from the prenatal transfer of maternal antibody, it indicates that the sex of the fetus differentially affected this placental process. The IgG receptor may have been up-regulated selectively on the placentas of female fetuses, compensating for reduced antibody in the disturbed mothers.(PsycINFO Database Record (c) 2016 APA, all rights reserved)