Neonatal infection can be acquired in the womb, passed through the placenta by the mother or through ruptured membranes, in the birth canal during delivery or from external sources after birth (postpartum). Maternal infections can cause a birth injury if undiagnosed and not treated. Infections to babies in the womb can occur any time before birth. The effect of the virus to the baby depend on the type of infection and timing of infection in gestation. This can have a devastating impact to the baby and can cause spontaneous miscarriage, intrauterine growth restriction, premature birth, stillbirth and congenital malformation.

Viral infections can include herpes simplex viruses, HIV, cytomegalovirus (CMV), and hepatitis B. Infections such as HIV or hepatitis B can be passed to the baby from passage through an infected birth canal or if delivery is delayed after rupture of membranes.

Bacterial infections include group B streptococci, enteric gram-negative organisms (primarily Escherichia coli), Listeria monocytogenes, gonococci, and chlamydia.

Group B Streptococci is a common infection and can be treated effectively following an early and quick diagnosis. If left untreated Group B Strep can be harmful to the baby and can affect brain development. On rare occasions, it can cause serious infections such as meningitis, sepsis or pneumonia.