Antepartum testing is a series of tests performed at the end of pregnancy to confirm fetal well-being. These tests are based on the baby’s heart rate and other characteristics.
The nonstress test (NST), biophysical profile (BSP), and the contraction stress test (CST) are all examples of antepartum tests.
Antepartum testing takes place after 32 weeks of pregnancy. This is so the doctor and the couple can be forewarned about any potential problems that could require further testing or the immediate delivery of the baby.
These results show the amount of oxygen and blood flow to the fetus through the placenta.
Pregnancies with a high likelihood of fetal complications are most likely to have antepartum testing. There are many reasons to have antepartum tests:
- A chronic condition in the mother such as high blood pressure and diabetes
- Problems with pregnancies in the past, such as stillbirths, may be a problem.
- Fetal complications include intrauterine growth retardation (a slowing down of the fetus’s growth) and .congenital disabilities.
- Problems in current pregnancy include preeclampsia (serious pregnancy-induced high blood pressure), gestational diabetes (pregnancy-related), premature rupture of membranes, excessive amniotic liquid (the liquid surrounding the fetus), vaginal hemorrhage, and placenta Previa (a condition where the placenta is placed over the cervix rather than near the top of the uterus).
- Twins and other multiple fetuses
Post-term pregnancy is one of the frequent reasons for antepartum screening. A normal pregnancy lasts 40 weeks. Pregnancy should be stopped if it continues past 42 weeks. Pregnancy testing should begin at 41 weeks.
There is an increased chance that the placenta will not meet the baby’s growing nutritional and oxygen needs after 41 weeks. This could be seen in reducing the baby’s movement, decreased amniotic fluid, and changes in the baby’s heartbeat pattern.
CST and NST use an electronic fetal monitoring technique to assess the heartbeat of the fetus. An ultrasound exam is required to determine the biophysical profile.
The NST is often the first test to confirm fetal well-being. The NST is based upon the principle that if the fetus moves, its heartbeat normally accelerates.
NST monitors the accelerations in the heart rate of the baby in response to their movements. These are also called movements without stress.
Medical personnel place an electronic monitor on the mother’s abdomen to monitor the baby’s heart rate. A graph or trace is created to determine if the baby’s heartbeat shows correct reactivity or acceleration.
The mother presses a button each time the baby moves on the tracing to record their movements. The mother might be asked to rub the baby’s abdomen to awaken it if it is not active.
Vibroacoustic stimulation is sometimes used to stimulate the fetus with a loud instrument. The test usually takes between 20 and 45 minutes.
If the baby is getting enough oxygen, they should move at least twice per 20-minute period. The baby’s heartbeat should rise at least 20 beats per hour for at least twenty seconds during these movements.
NST is the easiest and most affordable antepartum test.
The biophysical profile can be used to add information to the NST. The biophysical profile is an ultrasound examination that looks at the baby’s health and examines for abnormalities.
These include fetal movements, fetal tone, and breathing, as well as amniotic fluid volumes. A decreased amniotic fluid volume can indicate that the baby is under stress.
Each component of the test (NST) is scored. The scoring system is as follows: 2 for normal or present, 1 if decreased, and 0 for abnormal. 10. is the highest score possible.
Another option is the modified biophysical profile. This includes only NST and amniotic liquid volume.
CST is similar to the NST, except it evaluates the fetus responding to contractions in the mother’s uterus.
It is more complex and is usually used to confirm the results of an abnormal NST. Because they temporarily stop blood flow and oxygen, uterine contractions can cause stress in the fetus.
CST is used for confirmation that the heart rate does not decrease when the fetus is under stress.
CST can be performed using the same equipment used for the NST. The CST is performed with the same equipment as the NST.
It records maternal blood pressure and fetal pulse, along with the time, intensity, and duration of any spontaneous contractions. To perform an accurate test, the contractions must be sufficiently frequent and of sufficient duration.
An oxytocin stress test (OCT) may be performed if a uterine activity is not normal. An intravenously administered drug called oxytocin to the mother to trigger contractions is used during an OCT.
Self-stimulation of the mother’s nipples is another option, which releases natural oxytocin. The fetal heartbeat is monitored until three moderate contractions occur in a 10-minute period.
To stimulate fetal activity, the mother should eat right before the antepartum test.
The NST and the biophysical profile pose no significant risks. The biophysical profile uses ultrasound which is painless and safe.
It does not emit harmful radiation, and there has never been any evidence that sound waves can cause harm to the mother or the fetus.
The reason for the testing will determine how often it is performed. Sometimes, the test results are not correct and can lead to an unneeded early delivery or cesarean. It is important to repeat any abnormal results.
Normal or negative antepartum tests should assure that the baby is healthy. This should be enough to last for a few days without needing to deliver immediately.
False-normal results are possible, but this is not a common occurrence. It is vital to remember that even if all tests are normal, this does not guarantee a perfect baby.
If there are two or more distinct movements of the fetal heart and appropriate accelerations within twenty minutes, the NST is considered normal (reactive). A biophysical profile score between 8-10 is considered to be reassuring.
Normal CST means that the fetus does not show any decelerations in a heartbeat in response to three uterine cramps in a period of ten minutes.
Positive results indicate that the baby isn’t getting enough oxygen. It is possible, however, that the test result was not as expected.
Follow-up testing using the same test or another is done at least once a week to confirm or monitor suspected disorders.
If the NST is not normal (nonreactive), it means that the fetal heartbeat does not increase by at least twenty beats/minute at least twice in a twenty-minute period. Also, abnormal decreases in heart rate (decelerations) are cause for concern.
A biophysical profile score below 6 should be considered a cause for concern. Further testing should then be done. An immediate emergency delivery may be necessary if the score is below 4.
Late decelerations or abnormally slowing down fetal heartbeat after uterine contractions are examples of abnormal CST results.
This could indicate that the baby isn’t getting enough oxygen and may be having difficulty with the stress of labor or vaginal birth.
A C-section might be required to save the baby from the pain of labor. A severe deceleration, which is a slow or very rapid heartbeat, can indicate fetal distress.
The outcome of each woman’s situation will determine the outcome.
Sometimes, the woman’s individual situation will dictate whether she can postpone the delivery. At the same time, the medication is administered to the mother to treat high blood pressure or to the fetus to prevent premature lung development.
The doctor might decide to induce labor depending on the readiness of the mother’s cervical cavity. Extra-large fetuses of diabetic women may need C-section delivery.
Severe preeclampsia may also require a Cesarean section or induction of labor. The best direction of action will be determined by your doctor.
Bad results in antepartum testing could cause stress for expectant parents. Mother and father should discuss all results with their doctor.
Creasy, R., et al. Creasy, and Resnik’s Maternal-Fetal Medicine: Principles and Practice. 8th ed. Philadelphia, PA: Saunders/Elsevier, 2018.
Gabbe, S., et al. “Antepartum Fetal Evaluation.” In Obstetrics: Normal and Problem Pregnancies. 7th ed. Philadelphia, PA: Saunders/Elsevier, 2016.
Johns Hopkins Medicine. “Gynecology & Obstetrics: Antepartum Testing.” HopkinsMedicine.org . https://www.hopkinsmedicine.org/gynecology_obstetrics/specialty_areas/maternal_fetal_medicine/services/antepartum_testing_prenatal_diagnosis_treatment_center/ (accessed April 15, 2020).
American Congress of Obstetricians and Gynecologists (ACOG), 409 12th St., S.W., P.O. Box 96920, Washington, DC 20024, http://www.acog.org.