Thank you for your question. Yes, you are right a pregnant person is offered routine screening for sexually transmitted infections. The majority of STIs have phases where there are no symptoms and can go unnoticed unless tested. Even if the person has had an STI test in the past, testing again during pregnancy is routine.
Having an STI during pregnancy can result in serious conditions to the fetus and has been linked to low birth weight or miscarriage, among other complications. Testing is generally offered during the first prenatal visit to a doctor. If infections are identified, they can be treated to support a healthy pregnancy.
It is safe and normal to have sex during pregnancy, unless advised not to. If the pregnant person engages in penetrative sexual activity with new partner(s) and without a condom (internal or external), additional STI testing may be recommended. It is important for the pregnant person to have a open discussion with their health care provider for a safe and healthy pregnancy.