The choice of maternity wear included in the game is limited at best, so here's six items of game clothing enabled and morphed for pregnancy. These are all for Adult/Young Adult females. Included are:
T-shirt (Everyday, Sleepwear, Athletic)
V-neck sweater (Everyday)
Capri pants (Everyday, Athletic)
Fitted skirt (Everyday, Formal)
Sleep shirt (Sleepwear)
Short flared dress (Everyday, Formal)
Although these are game clothing, they will show in CAS as additional items with their own custom thumbnails indicating they are enabled for maternity. Unfortunately I couldn't find any way to simply add pregnancy to the in-game clothing and be able to choose them or even have them used randomly more than once in a blue moon, so these are basically custom clothes using the same in-game base meshes with different designs and an added pregnant morph.
They're fully plan-able, meaning if you have the sim wear these items before becoming pregnant she will continue to wear them.
Updated 8/9/10 to conform to the standard EA top and bottom pregnant shape. If you have problems with gapping between the skirt or Capri pants and other CC maternity wear that's bare midriff or tight at the waist, this should fix it.
If you don't already have it, it would be a good idea to grab my fix for the game maternity jeans, since without it they'll look pretty funny with the t-shirt or sweater. (This has also been updated to the standard shape on 8/9/10): http://www.modthesims.info/download.php?t=371019
Are these compatible with WA/Ambitions/Late Night/XXX expansion?
Almost certainly, yes. Unless the basic way the game handles morphs changes, there's no reason they wouldn't be compatible. Please try it, find out, and don't ask unless there's a problem. Sorry, but I'm getting VERY tired of seeing the same question on every morph-related mod I've done every time a patch or expansion comes out.
These are only morphs added to game meshes, so there are no additional poly counts.
Wes H. for his Milkshape plugins
Delphy for CTU
P.L. Jones for S3PE
** Update 7/14/2010
Wouldn't you know it, if you have Ambitions installed the new custom content symbol is right on top of the pregnant symbol I used to mark the thumbnails for this clothing. I've updated the package so the thumbnails have the pregnant symbol on the other side.
** Update 8/9/2010
Uploaded a new version that conforms to the EA standard top and bottom pregnant shape. This should fix problems with gapping between these and other CC maternity wear.