A straightforward term for a pregnant woman. The kanji 孕 means 'to become pregnant' or 'to conceive', and 女 means 'woman'.
I gave up my seat to a pregnant woman on the train.
Compound of 孕み (はらみ, 'pregnancy', the continuative form of 孕む 'to become pregnant') and 女 (おんな, 'woman').