Latent syphilis and pregnant. I'm being treated but how does this affect my baby 17wks preg?

Congenital syphilis. The risk to your baby is low. Dangerous consequences of congenital syphilis (infection of the baby in in utero) occur mostly in the last few weeks before delivery. You're way ahead of that and penicillin now will protect the baby against serious outcomes. If your latent syphilis is late (over a year with weakly pos blood test) the risk is even lower. Best wishes for your growing family!