Majikow the Kaua'i Marriott Resort is very nice with a great pool and a beach onsite. There are also a number of restaurants on property including Duke's which is very good at a reasonable price. It is also a good central location on the island to use as a home base to explore. If it turns out your wife doesn't feel like touring during your trip, it is also just a relaxing environment to hangout. I have stayed here a couple of times and also stayed once at the Kauai Lagoons MVCI property which is just up the road in the same complex. If you can get that one, it is wonderful. Ritz Carlton Grade Timeshare units with nice Lanai's and a good view and a free shuttle bus down to the Marriott for access to more services.

I haven't stayed there but the new Koloa Landing Resort at Poipu, an Autograph Collection property, looks great. Poipu is another great part of the island though less centrally located. You could also try to get the St. Regis (Starwood property) in Princeville which is also very nice area; however, it is the Northern most part of the island and far away from other activities. Princeville is a good place to stay for a few days as part of trip and then go to Poipu or Lihue. There are tons of vacation rentals at relatively reasonable prices in Princeville if you want to tack a few days on to your travel package.

Lots to do on Kauai including Waimea Canyon, Snorkeling, Boat Tours to see the Napali Cliffs. Kokee State Park, various hikes of all difficulty levels, sea kayaking, etc. We have been to the Big Island and liked it a lot; however, to do it well you need to split your stay between the Kona side and the Hilo side. Furthermore, the activities on The Big Island tend to be a bit more intense and probably not something you'd want to do in the third trimester of pregnancy (e.g. seeing the volcano or the Observatories on the summit of Mauna Kea).

Hope this helps...

--Jon

P.S. Hawaii is wonderful in general and hard to go wrong as long as you don't skimp too much on your accomodations. We have been to Oaho, Maui, Kauai, and The Big Island multiple times and liked all of them. Any of the full service Marriott properties or timeshare properties (harder to get) should be fine. I am less familiar with the Starwood properties but they also have lots of nice ones in Hawaii that are worth considering.