Women develop carpal tunnel syndrome at least three times more commonly than men. The reason for this is unknown but currently a topic of research. It has been proposed that the "swelling" we have during pregnancy--particularly in the third trimester--causes pressure on the nerve. However, many women develop this early in pregnancy (or even when they are using hormonal contraception). Women also develop it around and after menopause. It is suspected that there are genetic and hormonal reasons for this that go beyond "swelling."
Carpal tunnel syndrome symptoms can be treated during pregnancy. Splinting and (in some cases) corticosteroid injections into the carpal canal can provide relief. If you are pregnant and have symptoms, discuss the options with your OB or ask for a consultation with a hand specialist.