Neel, don't call yourself a sissy; you're a human being, and why shouldn't you be upset by such blame and undermining of your love and efforts for DS? The fact that you are considering the criticisms also means that you are not a stubborn old goat (like two others we are discussing), and are willing to compromise your own interests for the sake of your child.
I really liked stillfrazzled's quote of "until you are psychic, don't feel guilty" idea, and also MarineIguana's comment on over-protecting children! I take my DS out in weathers that MIL does not consider suitable - like rain , but because she is a reasonable person, she doesn't try to stop me doing that (at least - she does fuss about other things). She does have other bees in her bonnet, for example an unreasonable hatred of nursery - once suggested taking DS out for the rest of the winter "so he doesn't get ill" , but she doesn't go on about it all the time; she does try to control herself and her fears, and I really admire that. (I also think she will have an easier life if she stops worrying quite so much, but "ah shucks - that's just my humanitarian side showing")
As for that "eating well" bollocks, even laying aside the fact that it makes it sound even more like she has it in for you, we don't know that she isn't working to outdated or OTT ideas! One of DH's friends forced his wife to drink a large glass of milk and eat 2-3 eggs for breakfast when she was pregnant, which actually was the opposite of a favour, as she gained a lot of weight (she is very petite), which made it hard to get about while pregnant, and which was hard to lose! She took it well, but I would have been rather annoyed!
Maybe MIL is the problem, not DH, if she was having a go about you before the birth. Does that pre-date any blame your husband has levelled at you? What was your relationship like before? Was he in awe of your 400-page memorisations?!