Swelling in pregnancy might be due to two things: hormonal changes that occur in pregnancy, and slower circulation and lymph drainage. The slower lymph drainage is usually in the lower limbs and due to the pressure the baby puts on the big blood vessels in the abdomen and pelvis.
Actually everything below the level of the uterus might be swollen including the labia of the vagina that are made of connective tissue, which on the other hand can easily take additional amount of fluids and swell.
You might want to visit your gynecologist to check if this is the case or another condition is present.