i had one at 24 weeks with my DS. He had a heart defect that is often linked with downs and 22q deletion. his results came back all clear
it isnt a pleasant procedure. the ob said it felt like a blood test, afterwards i told him i was going to push a giant needle through his belly and he can tell me if it feels like a blood test!!
I had my mum at home with me for a few days after just to ensure i didnt pick up DD2 or hang out washing to make sure everything healed. there was no pain or bruising afterwards.
Wishing u all the best