Antenatal Testing - NST and AFI
Testing and monitoring are normal parts of care during pregnancy. But some pregnancies may require extra testing to
check the health of the baby more closely. In most cases the results of monitoring will reassure you and your doctor
that all is going well with your pregnancy. If your doctor has recommended you to complete NST and AFI testing then
don’t be alarmed.
The tests are simple, comfortable, non-invasive and safe. It takes approximately 30 mins – 1 hr. to complete both
tests. Most women enjoy these tests because they provide reassurance about the health of their baby, and also
because they get to hear the baby’s heart and see images of their little one.
Why is this special fetal testing needed?
Every patient and pregnancy are different. Your physician may order NST and AFI testing due to:
- Chronic medical conditions such as diabetes or hypertension
- Pregnancy related conditions such as preeclampsia
- History of problems in past pregnancy
- Abnormal ultrasound or test finding during the pregnancy
- Pregnant with more than one baby
- Pregnancy has lasted longer than 40wks
The Fetal Non-Stress test is a simple, non-invasive test performed in pregnancies over 28 weeks of gestation. This
common prenatal test is named “non-stress” because no stress is place on the fetus during the test. The primary goal
is to observe the heart rate of the fetus through a longer period of time, and this test is a good indication of
whether the baby is receiving enough oxygen.
During the test, 2 belts are placed on the mother’s abdomen; one to measure fetal heart rate and the other to
measure contractions. This test can be completed in our office and also at the hospital. The test is performed for
20-40 minutes (so make sure to bring a good book).
If your baby does not move for a while during the Non-Stress test, he or she may just be asleep. Your nurse may
suggest you have something to drink to make the baby active. A buzzer sound device may also be used to wake the baby
and cause movement to make sure it is doing well.
NST is usually performed twice a week until the baby is born.
In addition to the Non-Stress Test (NST), the doctor may order an ultrasound to measure the Amniotic Fluid Index
(AFI) level. Amniotic fluid surrounds your baby in your womb. It cushions your baby, helps the development of your
baby’s lungs, digestive system, and muscle development, and helps protect the umbilical cord from too much
The ultrasound technician will have you lie down on your back and will move the ultrasound transducer over your
abdomen. You’ll be able to see your baby on the monitor while the tech carefully measures the pockets of fluid
surrounding your baby. The measurements are added up to give your baby a score called AFI. AFI score of 5-25 is
AFI is performed once a week until the baby is born.