Your blood pressure, already low these days because of pregnancy, can dip even lower and cause lightheadedness -- which could result in fainting. "Women in the first or second trimester have a greater tendency to faint in the summer because the heat causes your blood vessels to dilate," says Dr. Harms. So how can you get the lightheadedness to pass? Dr. Harms suggests lying down on your left (heart) side to improve circulation. If you’re somewhere you can’t lie down, like a crowded subway platform, take a seat (ask someone to move for you!). Other tips include getting out of the sun, drinking some water, pulling over if you’re feeling woozy while driving, and staying well fed and well rested.