How will I know if my fetus is healthy?

Get Care! There is no one test to assure that your baby is healthy. The purpose of prenatal care is to optimize outcomes and put the most number of healthy babies into mother's arms. Early care and regular physician supervised care will identify any risks that are specific to your pregnancy. Ask questions and find an obg that meets your communication style and makes you feel comfortable.
You do! Believe it or not, only about 1% of all pregnancies have major genetic abnormalities. So...The assumption is, and should be, that your baby is healthy. Of course, you do need pre-natal care, and most patients will get a sonogram to assess fetal health. Remember: the reason you go the obstetrician is to prevent medical problems!