To the best of my memory, pregnancy of a player character has only come up once in my games. We had rescued a PC's husband from slavery, and her player decided to roll to decide whether their "continued relationship" resulted in her getting pregnant, and it did. If I recall correctly, she took a minor penalty to heavy physical activity, which thanks to the style of game we were playing, came up rather infrequently.
It was actually a great source of RP for us, as my character had earlier been established as wanting to protect her due to owing her father a life-debt, and was only with the group in the first place to ensure she survived while she dove head first into spearheading The Rebellion against The Evil Empire. Learning that she was pregnant and wanting to be a good great-uncle for the baby is what ultimately drove him from being the token Evil teammate (Pathfinder: Oracle of Asmodeus) into a lowercase g good person.
There was weeks of in-game downtime between sessions, and lots of sessions with little combat, which helped with the suspension of disbelief in regards to heavily pregnant women in martial combat. Plus, everyone was perfectly fine with the idea that in a world where healing magic was readily available and human sized creatures were durable enough to routinely fight monsters the size of small houses, the odds of complication were a lot lower.
It actually created a hilariously dark moment where we discovered a Slaver's Ring set (a set of rings that once put on, couldn't be removed without powerful magic, and one removable ring that allowed the wearer to know the location and health of the other wearers), and my character immediately went "this is perfect for the baby!" The soon-to-be-mother was not amused.