Fetal Biophysical Profile and Nonstress Testing
Dr. Marla Eglowstein
In use since the 1980s, the biophysical profile (BPP) and nonstress test (NST) are widely-used methods of monitoring fetal activity. Both allow doctors to determine that uteroplacental function is adequate.
In the late second and early third trimester, the fetus develops characteristic responses to its environment, including breathing and periodically increased heart rate. During a BPP, real-time ultrasound looks at fetal movement, tone and breathing, and each of these is counted for 30 minutes. During that interval, a fetus receiving adequate oxygenation should show:
•two or more discrete body movements
•one or more extensions or flexion of a limb (an opening and closing of a hand for example)
•one or more series of breathing events lasting 30 seconds or more (rhythmic diaphragmatic movements)
As part of the BPP, the doctor determines if the amniotic fluid volume is adequate by measuring a single vertical pocket of at least two centimeters (cm). Often BPP may be combined with nonstress testing. The NST continuously reads the fetal heart rate and uterine activity for 20 to 30 minutes.
The NST is considered reactive when the fetal heart rate accelerates at least twice, at least 15 beats per minute above the baseline, lasting at least 15 seconds, within 20 minutes. Without this response the test is nonreactive. When all four ultrasound components are normal, doctors may omit the NST. Or if nonreactive, the NST time may be extended to allow for a fetal sleep cycle.
The NST is assigned a score of 2 if reactive, 0 if nonreactive (inadequate). The doctor conducting the test assigns each of the four ultrasound components a score of either 2 (normal or present) or 0 (abnormal, absent or insufficient). A score of 8 or 10 is normal, a score of 6 is equivocal and a score of 4 or less is abnormal. Regardless of the overall score, the presence of oligohydramnios (the largest vertical pocket of amniotic fluid volume less than 2 cm) indicates the need for more evaluation.
The BPP and NST are used for fetal surveillance in many situations. Common indications for the exams are:
•decreased fetal activity
•maternal conditions affecting placental function, such as diabetes (both preexisting and gestational), hypertension, autoimmune disease and preeclampsia
•fetal conditions such as oligohydramnios, polyhydramnios, growth restriction, multiple gestation and known genetic or developmental defects
•post-date pregnancy
Normal BPP and NST results indicate adequate function of the placenta and normal reactivity of the fetal autonomic nervous system. When the doctor sees abnormal results, more monitoring is needed to determine the cause or to determine whether delivering the fetus is necessary.
Typically, pre-approval for BPP and NST by a health plan provider is not needed. However, because BPP and NST are based on fetal responses that develop in the late second and early third trimester, normally they are not applicable before 24 weeks. Tests prior to this would be exceptional and case managers should look closely at them. Whenever doctors conduct the tests before 40 weeks, they should note reasons in the patient’s record. Without this documentation, whether or not the test was needed can be questioned. After the expected date of delivery, BPP and NST also become part of routine pregnancy care.