Any food from chain places will be fine I'm sure. McDonalds don't allow their staff any judgement in the cooking process and actually have timers on everything which beep when the food is done (you'll hear them now I've mentioned it). The burgers are so thin there is no way they could undercook them.
If that's what you fancy, go for it!
I've had McDonalds a couple of times since being pregnant (not really that much of a fan but sometimes I just fancy it). If you want to be ultra careful avoid the milkshakes/icecreams as they are Mr Whippy type things which can be a problem but again, from McDonalds, which has such strict hygiene standards there probably isn't that much of a risk.
I'd worry more about the late night, unbranded pizza shop on the high street than anything with a name. That said, I've had food from there as well and been fine. Our town gives everywhere hygiene ratings which are publicly available (and should be displayed in the shop) so you know if you find somewhere with a D not to eat there. McDonalds is B (not sure I've seen anywhere with an A).