TheGentlemanDM: For reference, our closest relatives have gestations of 230 (chimp) and 257 (gorilla) days, compared to our 270. Rhesus monkeys gestate for 164 days, baboons for 187.
Our gestation time has slowly lengthened as we evolved to be a larger species, and could feasibly continue to do so. Essentially, bigger animals need longer in the womb.
Judging by the 8 month chimp, and the 8.5 month gorilla gestations, it has at least been close to 9 months for as long as we’ve been recognisably human. Where it gets interesting is whether or not this span will make an upward or downward trend in the future- and I’d estimate upward.
The average height of a human has increased greatly over the past century due to availability of nutrition. Larger mothers have larger children, which would hypothetically need a longer gestation. However, this is environmental, and hasn’t necessarily been selected for in our genes.
Humans have also hit a roadblock on gestation- we’re limited by the size of the birthing canal. Our massive brains need to develop, and if they were any larger at birth, we wouldn’t be able to be born.
(This is why human babies are so helpless- that giant brain is basically a blank slate at birth because it wants more development time, but can’t get it in the womb.)
With increased availability for C-sections these days, women having very large babies can still safely deliver. And these over gestated children, which otherwise wouldn’t be born, are able to survive and enter the gene pool.
All of these lean towards a longer gestation. However, at the same time, medical advances mean that children who are born prematurely are also able to survive and enter the gene pool when they otherwise wouldn’t.
So all up, I don’t think we’ll see much change in our gestation time in a hurry. Over a few million years, it might move a week or two either way.
tldr; a) No, with a but, and b) yes, with a but.