With my first they wanted a 2nd ultrasound to see her face more clearly. I was told not to worry that follow up ultrasounds are very routine. They just "need to rule out cleft pallet". So of course for two weeks I was obsessed with 'cleft pallet'. I cried and cried. My husband tried desperately to reassure me. Blah to worrying. She was fine, beautiful in fact.
With my sister's 4th she was told they couldn't find her babies right arm. She had to go to a specialist a few weeks later. My sister was told there was probably nothing to worry about. She tried to keep herself from worrying at the same time she read everything the internet offered on amniotic banding. Her follow up was clear, and her baby is perfectly healthy, fully intact.
When it comes down to it 'rational thinking' doesn't always go hand in hand with needing a follow up ultra sound. Give yourself lots of room to breath, relax, and if you need to worry a little bit. But remember that odds are on your side. In a few weeks you'll be able to see your precious little one again, and that is always a good thing!
Blessings to you and all other mamas that have to go through this!