How often should the baby's heart be monitored if i have a family history of lupus?

Depends: It depends on whether you, yourself, have lupus or not.

SSA / Ro status: The most important thing is to know your ssa antibody status (sometimes called ro antibody). If you are ssa / ro positive, your baby needs extra monitoring.

No more frequently: Not any more often than it would be monitored if there was not family of lupus. It does not depend on whether or not you have lupus. Any problems with heart block from lupus will be detected at birth.

Lupus and heart: How old is your baby... Lupus (with anti-ro and anti-phospholipid antibodies) can result in congenital heart block in fetus/newborn. Please speak to your physician if concerns.

Lupus: At this point have the baby checked by a pediatric rheumatologist thoroughly . Patients pregnant with lupus especially with certain anti bodies need to be monitored from maternal and fetal stand point by an experienced rheumatologist during pregnancy and soon after child birth .From your question it appears you did not have lupus during pregnancy and it was more of a family history of lupus.