What is a common maternal factor that can lead to thrombocytopenia in newborns?

Drug ingestion is indeed a common maternal factor that can lead to thrombocytopenia in newborns. Certain medications and substances can adversely affect platelet production or survival in the fetus. For instance, maternal use of substances such as alcohol, certain anticonvulsants, and nonsteroidal anti-inflammatory drugs (NSAIDs) has been associated with lower platelet counts in infants.

This can occur due to direct toxic effects on the fetal bone marrow, altered hematopoiesis, or immune-mediated destruction of platelets. It's crucial for maternal healthcare providers to screen for drug usage and counsel pregnant women about the potential risks of certain medications.

Other factors listed, while they may have implications for maternal and fetal health, do not have as clear of a direct link to causing thrombocytopenia in newborns as drug ingestion does. Increased activity during pregnancy, excessive dietary iron intake, and excessive weight gain may have various health impacts, but they are not typically associated with causing decreased platelet counts in newborns.