You seem to think that pregnant women having to work hard is some sort of rare occurrence on the level with performing surgery on yourself. It isn't. My mother worked as a cleaner up until a few days before I was born. A good friend of mine works in childcare, also worked right up until a few days before labour (4 times!) My pump instructor was still teaching classes (4 a week!) up until two weeks before she was due. These are all physically demanding jobs.
And these stories come from the rich, well-to-do West. In developing countries many women don't get the luxury of things like maternity leave. Women work hard as long as they can and get back to work as soon as they can.
Does pregnancy slow a person down? Not at all in the early stages. Somewhat in later stages. Can a heavily pregnant woman say to herself "naughty word that!" and power on through discomfort to do what needs to be done? Yes. Obviously. And all of this before we assume that PCs are made of sterner stuff (in the classic heroic mould) than we mere mortals.
If you want to give a penalty to attack because of a large belly and out of whack abdominal muscles?* Go for it. But if you're going to be this " realistic" don't forget to give pregnant women increased hit points & fort saves to represent better tolerance for pain.
As for the penalties you list to mental prowess, really? "Baby brain" is not a real thing. A pregnant woman in a dangerous situation is going to have more Will** to fight and survive than most.
*You can compensate for this with back muscles. Tiring? Sure. But you know, higher pain tolerance and all that.
** capitalised to indicate it's being used in the game jargon sense, as well as the common English usage.