Fetal Treatment Program of New England

Fetal Assessment

Sometimes we need to check the health of your unborn baby. The Prenatal Diagnosis Center offers a non-stress test, biophysical profile and amniotic fluid index.

Non-stress Test

A non-stress test (NST) uses a fetal monitor to examine your baby’s heart rate over time (usually 20 to 30 minutes, but sometimes up to an hour). The monitor has two sensors that are placed on your belly with two belts that go around your waist. One sensor detects any contractions you may be having—including those you can’t feel—while the other sensor tracks your baby’s heart rate, which you will be able to hear. As you sit in a reclining chair during the test, a nurse watches your baby’s heart rate, making sure that it increases when your baby moves.

Results are categorized as follows:

  • Reactive NST. A NST is considered reassuring if the fetal heart rate increases at least 15 beats per minute over the baseline (between 120 and 160 beats per minute) and lasts at least 15 seconds, within a 20-minute timeframe.
  • Nonreactive NST. If these accelerations do not occur, the test is said to be nonreactive. Although a reactive NST is a good sign, a nonreactive NST does not mean there is something wrong with your baby. The baby might be sleeping or require a longer NST or biophysical profile.

Biophysical Profile

A biophysical profile (BPP) is an ultrasound exam that monitors the movement, body tone, breathing efforts, amniotic fluid volume and fetal heart rate of your unborn baby. Each measurement is given a score of zero to two points, which is then totaled. An additional two points are added if there has been a “reactive” fetal heart rate.

Results are categorized as follows:

  • A high score of 8 to 10 means the fetus is in good condition inside the womb.
  • A low score of 0 to 4 usually means that the fetus needs to be delivered.
  • A score of 5 or 6 usually requires a repeat test within 24 hours.

Amniotic Fluid Index

The amniotic fluid index (AFI) is an ultrasound exam that measures the amount of amniotic fluid in your womb. Amniotic fluid may need to be measured for several reasons: perhaps you are past your due date or you have a history of your water breaking too early in a pregnancy. The BPP and AFI tests take approximately one hour each and are performed without discomfort for the mother or unborn child.