Antepartum Fetal Testing

What is a nonstress test?
A nonstress test (NST) measures the fetal heart rate in response to the fetus' movements. Generally, the heart rate of a healthy fetus increases when the fetus moves. The NST is usually performed in the last trimester of pregnancy.

Test results of the NST may be:
  • reactive (normal) - two or more fetal heart rate increases in the testing period (usually 20 minutes).
  • nonreactive - there is no change in the fetal heart rate when the fetus moves. This may indicate a problem that requires further testing.
A nonreactive NST does not always mean there is a problem with the fetus. The fetus may simply be asleep. Or, it may be nonreactive because of fetal immaturity or due to medications the mom is taking. It is common for preterm fetuses, especially those before 28 weeks, to have nonreactive nonstress tests. Additional prenatal testing may be necessary.

What is a biophysical profile (BPP)?
A biophysical profile (BPP) is an ultrasound evaluation of the fetus and amniotic fluid and may also include an NST (non-stress test) (link to above). Biophysical profile testing is usually performed in the last trimester of pregnancy.

There are four to five parts to a biophysical profile. Four areas are assessed by ultrasound:
  • fetal breathing movements
  • fetal movements
  • fetal tone
  • amniotic fluid volume
The fifth area is the non-stress test which may be optional based on physician preference and patient history

What is a Doppler flow study?
Doppler flow is a type of ultrasound that uses sound waves to measure the flow of blood through a blood vessel. Waveforms of the blood flow are shown on the ultrasound screen. Doppler flow studies may be used to assess blood flow in the umbilical blood vein and arteries, fetal brain, and fetal heart. Doppler flow is sometimes called Doppler velocimetry. A Doppler flow study is often used when a fetus has intrauterine growth restriction (IUGR), which means the fetus is smaller than normal for his/her gestational age.