Maternal-Fetal Interactions
Core concepts
Understand maternal-fetal immunologic tolerance, placental transfer of IgG (predominantly third trimester), and the consequences for neonatal immunity and passive antibody-mediated disease (e.g., alloimmune thrombocytopenia, neonatal lupus from maternal autoantibodies). Know how maternal conditions-diabetes, hypertension, thyroid disease, and autoimmune disease-shape fetal development and placental histology. Grasp the pathophysiology of maternal diabetes effects: hyperglycemia drives fetal hyperinsulinism, macrosomia, and increased risk of caudal regression and cardiac septal defects with poor glycemic control.
Be able to reason about Rh and ABO incompatibility, hemolytic disease of the fetus/newborn, and the role of Rh immunoglobulin prophylaxis. Understand vertical transmission windows for infectious agents and the concept of TORCH screening-its limits and its interpretive pitfalls.
Traps
Questions conflate passive transfer of cells (fetomaternal hemorrhage, microchimerism) with transfer of antibodies. Another trap: assuming all neonatal thrombocytopenia is immune; consider infection, chromosomal disease, and congenital marrow failure. Rh disease requires sensitization, so a first pregnancy is typically unaffected-questions exploit this. Also remember that maternal IgG can produce transient neonatal disease even when the infant's own genetics are normal.
Worked example / rule of thumb
A neonate with petechiae and severe thrombocytopenia born to a mother with immune thrombocytopenia: consider passive transfer of maternal antiplatelet IgG, which clears over weeks. Rule of thumb: "Antibody-mediated neonatal disease is transient; cell-mediated or genetic disease persists."