"We use Doppler in the clinic to detect the heartbeat because it's more readily available than ultrasound machines," says Layan Alrahmani, M.D., a board-certified ob-gyn, maternal-fetal medicine ...

A Doppler device is a small, portable machine that uses ultrasound waves to detect and magnify the baby's heartbeat. Doctors use this test during most office visits to verify that the baby is alive.