First Congrats on both your trip and your little bun!!!!
For the crowds I have to say these days it is so hard to call what they are going to be like. Between the change in how schools schedule their spring breaks, the economy and everything else it really is kind of hard to call. I do agree it seems that DLR seems to be losing its slow/down seasons and becoming harder to predict and just busier overall.
I usually say go in expecting things to be busy and then you can only be surprised.

I would suggest having a plan of what you really want to do ride and show wise and work from there. Don't forget to use the FP system and just have fun!
As for being pregnant I can help you lots with that as I just went last week at 17 weeks and plan on going back next week too for my fourth pregnant trip, third knowing I was pregnant.
There are actually lots of things you do and they are not all kids rides. Any ride that does not have a height restriction is "safe" in pregnancy this includes all the Fantasyland rides, all Bugs land rides I believe, HM, POTC, Toy STory and Buzz Lightyear. Personally I am ok on going on a few height restricted rides as well depending on why they are restricted like I would probably do Splash (though I rarely ride it in general), Autopia, and Soarin.
There are also lots of shows, parades and other things that you can do to fill the time that use to be filled with thrill rides.
The big thing for me is bringing a water bottle I can fill so I know I am keeping hydrated which is very important pregnant. Use shows to relax and get off your feet so you don't over do it. Have snacks in your bag so if you something NOW you have something. I brought nuts and fruit leather to help keep myself going between snacks and meals

Also DLR has lots of bathrooms all easy to find and you will find them

If you take care of yourself you will have a great time!