Hi K.,
My number 1 pick would be Puerto Rico. If you are having a "good" pregnancy and are fairly comfortable, it's a great getaway. There are lots of wonderful beaches, playgrounds, rainforest walks, scenic drives, old San Juan forts and a full range of accommodations many of which include pools. Check out www.gotopuertorico.com. We've had good luck renting a small home or condo which gives you kitchen and laundry facilities. The prices are in line with good hotels. Check out www.vrbo.com and www.homeaway.com for home rentals.
I also love www.tripadvisor.com for traveler reviews of hotels.
Have a great time planning.