They may go away, they may not.

Best to stay off your feet whenever you can to reduce the pressure on your veins (the issue is the veins not being able to fight against gravity, so the blood flow kind of "backlogs," and pools, rather than neatly flowing). They're definitely not something only really heavy people get, but pregnancy does bring them out in a lot of people.

You can always have them removed if they don't go away on their own after you've given birth.