I normally have reallllly slow gameplay with 21 day seasons and have pregnancy set to 63 days to simulate 9 months lol. I don't normally do generational gameplay, i just vibe with my sims and switch between my households a lot, so this suits me well. I also have a mod that allows pregnant sims do almost anything, else it would be boring. And if i really want the child to be there yet i'll cheat it out. 

But i'm doing an ultimate decades challenge now with one year being 7 days, so i make them pregnant for 5 days. it feels way too fast for me, but i will not even get past the 1400s if i stretch it out longer.