St. Luke’s Maternal Fetal Medicine

Nonstress Test

The nonstress test or NST may be performed after 30 weeks gestation or about six months pregnant, when indicated for maternal conditions such as diabetes or high blood pressure and fetal conditions such as poor fetal growth or low amniotic fluid. This is usually performed once per week or two times per week depending on the woman’s caregiver preference.

The NST is performed with the pregnant woman comfortably positioned in a recliner, with an external transducer placed on her abdomen to monitor the fetal heart rate and another transducer placed on the upper abdomen to monitor uterine activity such as contractions. The monitoring lasts from 20 – 40 minutes.

A “reactive” NST is when the baby’s heart rate rises to a certain point above the baseline heart rate at least two times in a 20-minute period. Acoustic stimulation can be used to “wake” a baby that may be in a sleep cycle, which usually makes the baby move and raises it’s heart rate on the monitor. If a NST is not reactive within about 40 minutes, the woman’s caregiver is notified for further instructions or testing.