Congratulations on becoming a parent very soon, if not already.

The combo carseat+stroller contraptions do get to the gate for gate checking in the US, but you may want to disassemble them for security screening and the gate checking, assuming the carrier and TSA allows it to go airside. I have seen such things make it to the gate of my AA flights and get one or two valet tags. Make sure to get two valet tags if you're not able to take the car seat into the cabin in the off-chance that there's a spare seat next to you/your significant other to use for the car seat and a child who would otherwise be a lapchild infant.

Put the car seat and stroller in a protective bag of some sort, if only to reduce the chances of grease and other dirt making contact with the stroller/car seat and getting on the child or the parents thereafter.

Even with a protective covering, when these items are gate-checked (or even checked in at the check-in counter), they aren't always handled with the greatest of care by baggage handlers. I have seen strollers tossed from up high and onto the ground or thrown down shoots only to crash into the ground rather hard.