i know of a baby who was 5 months old before they detected a cardiac condition.
I know of a twin who was born with a hip condition - only recently diagnosed and he is almost 4.
In fact in the hospital when dd1 was having her cardiac surgery a few babies/children ahd been born without cardiac conditions being present.
My dd2 and 3 have a 1 in 50 chance of having what their father has ( he was only diagnosed with congenital cardiac condition in his 40's!!) Whilst they were both checked out in utero - unfortunately it is not able to totally ruled out or in until they are around 3 or 4 - when an echo gives a better view of the heart. Dd2 has had her scan but dd3 is not old enough yet.