Final answer:
During fetal development, maternal antibodies transferred to the baby provide passive immunity that lasts up to 6 months after birth, with IgG antibodies crossing the placenta and IgA through breast milk.
Step-by-step explanation:
The nurse assures an anxious primigravida that during fetal development from week 34 and beyond, maternal antibodies are transferred to the baby. These antibodies provide passive immunity for the baby, which lasts for a significant period after birth. The correct answer to the question of how long these antibodies provide immunity for the baby is d. 6 months.
Natural passive immunity involves the passage of antibodies from a mother to her child, with IgG being the only antibody class that can cross the placenta. Once transferred, these antibodies give the newborn protection from certain infections, due to the immunological memory based on the pathogens to which the pregnant person has been exposed. Secretory IgA antibodies, transferred through breast milk, also play a role in protecting the infant.
While passive immunity provides immediate protection, it does not induce lasting immunological memory in the baby, which means this form of immunity will eventually wane and require the baby's own immune system to take over.