YANBU to expect a thank you message for a gift, that is totally rude IMHO. However the checking on the pregnancy, it just sounds a little stifling if it's more than a congrats, are you well etc?
Perhaps they were the type of women who didn't want you checking constantly? I know I didn't like the attention and constant baby chitchat, i had a job and a life other than that, and i wanted to enjoy it before it went up in smoke for a while!
My mate thanked me for just being normal about it, and not gushing, tummy rubbing, wanting all the detail, as she felt she stopped being a human in her own right!
Also TBH, once you've done the pregnancy thing, it gets a bit, well boring. They are probably onto the next stage now....whether that be weaning, walking talking, schooling, that is relevant to the childs age.
My uni buddy had a baby 6 months before me, and we have remained the closest because we always have the same thing in common with our ds's and they play well together and allow us to catchup. Plus we have the same outlook, career, family, etc and aren't baby bores as some of my friends have become (not that i am implying you are, just saying people react differently).
It might be a good idea to reach out of your social circle, NCT groups are where people make a lot of good friends as you are experiencing the same things at the same time? MN meets in your locality?
It's hard, but you do grow out of friendships, and you should grow out of "duty" friendships, which it sounds like these are becoming. I had a male best mate, for 20 years, we travelled the world together, once he met someone he dropped me like a sack of spuds! It was hard, but i have made close adult friendships that i think have more longevity and support. Strangely enough my closest mate is a gay ex colleague and his partner, we are so different, yet so close!
I think you do have to cut a bit of slack too, it is soo hard keeping a family, career, marriage on constant boil and trying to keep up contact with others doing the same! Sometimes I get a card and realise that it's been behind the breadbin for 4 weeks! Ouch 