California has no "Romeo and Juliet" defense. Under 18 is a crime. Period. If within 3 years, it s a wobbler and most often charged as a felony. If, in an interview with police, there is an admission of certain other sexual acts, these can also be charged and are felonies. The former (PC 261.5) is NOT a registerable offense in CA, but the others can be.
As for doctors, medical professionals in CA are NOT mandated to report consensual sexual encounters if the minor is 16 or older, even if the partner is an adult. Unless there is the possibility of force or coercion, it can be a violation of HIPAA for medical offices to report these offenses. There is no law that mandates medical reporting under the scenario as laid out here. This has long been a frustrating element of the law in CA.
However! WHEN the child is born and mom seeks financial aid, you can bet that there will be an inquiry, the name sought, blood tests ordered, and the police called.