Non-Stress Test (NST) What? This test measures your baby’s heart rate and records any contractions of your uterus. Why? This test helps gauge your baby’s well-being. Normally, a baby’s heart will beat faster (accelerate) when he/she moves. This suggests that the placenta is delivering enough oxygen to your baby’s brain and heart and that is doing well. How? You will lie down or recline, and two straps with monitors will be placed around your abdomen. One monitor measures your baby’s heart and the other picks up any contractions. The data is recorded by the machine.