What happens when you deliver a baby vaginally, and you have an untreated std?

It depends. The effect that untreated stds have on a baby who was delivered vaginally depends on the std. Some stds may cause repiratory lesions, preterm labor, low birth weight, eye infections, pneumonia, death or still birth, deafness, blindness, meningitis, etc. Early prenatal care is vital to prevent transmission of disease from mother to baby.
Baby can get it. Sexually transmitted infections like gonorrhea, chlamydia, and syphilis can pass from the mother to the baby in the birth canal. They can cause very serious problems for the baby, such as blindness, brain damage, and even death. If the patient may have an std and is pregnant, they should see a doctor as soon as possible.