How can some sexually transmitted infections pass from a mother to a child before or during birth?

Sexually transmitted infections (STIs) can be transmitted from a mother to her child through a process known as vertical or perinatal transmission. This can occur during pregnancy, labor, delivery, or through breast-feeding.1

• HIV: The virus can be transmitted across the placenta during pregnancy, during labor and delivery, or via breast milk. Without preventative measures, the risk of transmission is significant, but it can be reduced to less than 2 percent through the use of antiretroviral drugs by the mother and newborn, as well as formula feeding. In some cases, an elective cesarean section may also be used to lower transmission risk.12
• Syphilis: This infection is transmitted to the fetus of an untreated pregnant woman, most commonly when the mother becomes infected during pregnancy, though prior infection also poses a risk. If untreated, it can lead to miscarriage, stillbirth, or severe congenital defects in the infant, including pneumonia, skeletal abnormalities, and long-term damage to the central nervous system. Antibiotic treatment, such as penicillin, can effectively prevent this transmission.34