Pregnant and peeing blood. Ring healthdirect Australia on 22.05.2018 Niramar 5 Comments First trimester: Blood in urine pee isn't usually caused by anything serious but you must get it checked out by a GP. Could my operation have affected my sperm count? About 2 percent of pregnant women develop these kidney infections, called pyelonephritis, most commonly in the late second or early third trimester. It's caused, at least in part, by the pressure of your uterus on your bladder. Constantly vomiting during pregnancy. Health conditions. Tell your doctor about any leakage so she can rule out an infection.