Heating pads are safe to use during pregnancy with proper precautions.
According to the American College of Obstetricians and Gynecologists, heating pads can be used to help reduce low back pain during pregnancy, but they should be used at the lowest possible setting 1 and wrapped in a towel to prevent burns.
Using heat on the body helps to improve circulation, relax the muscles, and reduce pain and stiffness 2 . Although pregnant people are generally advised to avoid heat exposure due to the risk of fetal abnormalities and pregnancy complications, heating pads on an isolated area are unlikely to raise your core body temperature 3 to that associated with neural tube defects (>39 degrees Celsius, 102 degrees Fahrenheit).
Taking a warm bath or shower can also be helpful in relieving pain. Newer research 4 suggests that pregnant people may be able to sit in a hot bath or sauna for up to 20 minutes without their core body temperature reaching dangerous thresholds, but any use of heat in pregnancy should be discussed with your healthcare provider prior to use.