When women (not you, troons) get pregnant they are recommended to get up to date with vaccines, because the antibodies and other certain chemicals/drugs can cross the placental barrier and influence the foetus. I suspect the current advice is only because we don't have long term data required to back up the advice to have it.
If your baby is gonna be a mutant it's because something happened in the first trimester. After this point you're relatively safe, if something does go wrong it almost always results in miscarriage/stillbirth.
Tldr Xander is only going to be as retarded as his genetics dictate