What Should I Expect If My Doctor Orders A Non-Stress Test?
If your doctor orders a fetal non-stress test (NST) it is not necessarily something to worry about. He/she may just want to be sure that all is well with your baby especially if it is past your delivery date. It is non-invasive and called “non-stress” because no stress is placed on your unborn child during the procedure.
What is a fetal NST?
A non-stress test measures:
- Fetal heart rate
- Reactivity of the fetal heart to movements
Its main purpose is to determine if the fetus is in distress. Healthy babies will respond with an increased heart rate during times of movement. The heart rate will decrease at rest. The premise of this form of prenatal testing is that adequate oxygen is required for fetal activity and heart rate to be within normal ranges. The fetus may not respond normally when oxygen levels are low. Low oxygen levels can often be caused by problems with the placenta or umbilical cord.
When is a fetal non-stress test done?
The NST may be done any time after 24 to 26 weeks (usually at 28 weeks). Most mothers who are advised to have them done will do so in the third trimester of their pregnancy. It may also be combined with a biophysical profile. There are no significant risks to you or your baby associated with a non-stress test.
When will you be asked to do a non-stress test?
The non-stress test indicates if your baby is not receiving enough oxygen because of placental or umbilical cord problems. It also highlights other types of fetal distress. You may be asked to do a non-stress test during pregnancy if:
- You sense that the baby’s movements are less frequent than normal
- You are overdue
- There is any indication that the placenta is not functioning adequately
- You are at high risk for any other problems e.g. preeclampsia, diabetes or have multiple gestations that may require an early delivery
- You have previously lost a baby in the second half of your pregnancy
How is an NST done?
- You may be asked to sit in a chair, or lean back on a gurney or exam table
- A stretch belt monitor is placed around your belly.
- There are two monitors fastened on to you:
- One will monitor your baby's heart rate (cardiotocograph)
- The second senses uterine contractions
- You will be given a clicker which you have to press each time you feel the baby move
- The monitoring may last from 20 to 40 minutes
- A baby who moves a lot and has a normal heart rate is classified as "reactive." It indicates that blood flow (and oxygen) to the fetus is adequate. He/she is considered healthy and likely to remain so for the next three to seven days.
- A "nonreactive" baby may lead to more tests to detect fetal distress. An early delivery might also be considered.
- If the baby does not move, it does not necessarily indicate that there is a problem. There could be other reasons for the baby’s non-reactivity than poor oxygenation. For instance, the baby could just be asleep. In such cases the nurse may use a small “buzzer” to wake the baby for the remainder of the test.
It could also be caused by certain maternal prescription or non-prescription drugs). A non-stress test reassures you that all is well or indicates if the baby needs to be delivered immediately. It helps reduce the risk of complications while increasing the chances of a positive outcome.
Dr. Jorge L. Gomez earned his Medical Degree in 1990 at Central Del Caribe University in Bayamon, Puerto Rico. Following residency in Obstetrics and Gynecology at Bronx-Lebanon Hospital center in the Bronx, NY (1990–1994), he completed additional fellowship training at New York University Medical Center NY, specializing in Maternal Fetal Medicine (1994-1996). After his fellowship in 1996 he joined South Florida Perinatal Medicine. Dr. Gomez is Board certified in OBGYN and Maternal Fetal Medicine. From 2003–2007 He was a reviewer for the American Journal Of Obstetrics and Gynecology.