Your cat is showing some jealousy because he knows you are pregnant and he is afraid you will show him less attention. It happened to me and my mom MANY times. What I do, give him shower of affection, buy him toys, a cat tree and a cat stand BY the window so he can look out the window to keep him busy and calm.
Do you watch Houseat House call
http://www.housecathousecall.com/Default.aspx on Animal Planet. I noticed every cases the vet suggested the cat owner to provide grass and a cat stand by the window to calm the cats.
Example of cat stand

is ideal for cat owners to have. I had one (man-made) and it was VERY useful for all of my 5 cats. I'm telling you, before we had that, the cats would go WILD and go into EVERYTHING. It was frustrating. My friend wanted to get rid of his homemade cat stand for $5... I took it and put it by the window...the cats LOVED IT and I noticed their attitudes toned down.
Might be worth a try. You could always buy a smaller cat stand at Walmart or Target.
My landlord's cat Tornado is always hissing at us even tho we didn't do anything. I bought Feliway diffuser plugin and it worked! It's sold at Petsmart
http://www.petsmart.com/product/inde...ductId=2755197
If you don't want to buy the plug-in, you can buy the Feliway Cat Pheromone Spray or any spray that has pheromone. It calms the cat. What I do on visitors before they come in the house, I spray the pheromone spray on the legs (that's where the cats tend to rub first) then welcome the visitor inside. As for you, I would spray the pheromone on your pants and walk toward the cat... do not make eye contact. Cats HATES eye contact. Just act normal and sit near the cat. Let the cat come to you. Cat hates CONTROL from humans. They like to be in control.
Good luck!