STDs/STIs can be caused by bacteria, viruses, yeasts, parasites or insects. They are transmitted through sexual contact like intercourse, oral sex or sharing needles. Pregnant women are at particular risk of transmitting infections to their babies before or during birth. While some infections like HIV, gonorrhea or herpes pose high risks, steps can be taken to reduce transmission like screening, treatment or C-section delivery. CMV infection affects about 1% of births and can cause deafness or disabilities if transmitted, though fetal testing and potential early termination are options considered.