In plain words
Transplacental IgG is the type of antibody that passes across the placenta from the birthing parent to the baby. Most of it moves in the third trimester, so a baby born at term has more than a baby born early. These antibodies protect against some infections the parent has had or been vaccinated for. Their levels fall over the first three to six months, while the baby makes its own immunity. This is why vaccines in pregnancy can matter for the baby. It is a temporary shield, not lifelong protection. Your pediatrician can explain how the baby's own vaccine schedule fills the gap.
The deeper version
IgG is the antibody class that crosses the placenta, by FcRn-mediated transport across the syncytiotrophoblast. Transfer is predominantly in the third trimester, so term infants are born with maternal titers that wane over the first three to six months, while preterm infants receive less. Passive protection against , influenza, and other infections is the rationale for maternal vaccination. The duration of protection, and whether maternal antibodies interfere with infant responses to vaccines, are active research areas.
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What mothers here say about transplacental IgG
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Sources
- Palmeira P et al. — IgG placental transfer in healthy and pathological pregnancies, Clinical and Developmental Immunology 2012
- American Academy of Pediatrics — Red Book: Report of the Committee on Infectious Diseases