It doesn't stop once the baby is born. Our third was a boy after two girls and for three years now we've heard "lucky he was a boy, you'd have to go again!" Now pregnant again and we hear "hope its a boy, even out those odds!"
I honestly think people have no idea what to say and will say it and then later go 'that was stupid'. Then again, you have people who are just silly in general and say silly things with no afterthought.
I'm so tired of it this time around I've swapped to telling people it's most definitely an indominous rex.