The Prenatal Ultrasound - biophysical profile (BPP)

This is a noninvasive test that predicts the presence or absence of fetal asphyxia and, ultimately, the risk of fetal death in the antenatal period. When the BPP identifies a compromised fetus, measures can be taken to intervene before progressive metabolic acidosis leads to fetal death.

The BPP combines data from two sources, ie, ultrasound imaging and fetal heart rate (FHR) monitoring. Dynamic realtime B-mode ultrasound is used to measure the amniotic fluid volume (AFV) and to observe several types of fetal movement. The FHR is obtained using a pulsed Doppler transducer integrated with a high-speed microprocessor, which provides a continuously updated reading.

Originally described by Manning and colleagues, the BPP has become a standard tool for providing antepartum fetal surveillance. The BPP integrates 5 parameters to yield a biophysical profile score (BPS) and includes (1) the nonstress test (NST), (2) ultrasound measurement of the AFV, (3) observation of the presence or absence of fetal breathing movements, (4) gross body movements, and (5) tone. Table 1 describes specific criteria for the BPS.

The BPP allows 2 points for each parameter that is present, yielding a maximum score of 10; however, if all the ultrasound variable findings are normal, the FHR variable may be excluded because no change is made in the predicative accuracy of the BPP by including the FHR. If one or more ultrasound variable findings are abnormal, the NST should be performed.

A basic principle of antepartum testing is that a more accurate prediction of fetal wellness is achieved in direct proportion to the number of variables considered. The BPP is a clinical tool that integrates levels of dynamic biophysical activities into a useable standard. The BPP allows 2 points for each parameter that is present, yielding a maximum score of 10; however, if all ultrasound variables are normal, the FHR variable may be excluded because no change is made in the predictive accuracy of the BPP by including the FHR. If one or more ultrasound variable is abnormal, the NST should be performed.

Table 1. Criteria for Coding Prenatal Ultrasound Variables as Normal or Abnormal

Biophysical Variable	Normal (Score = 2)	Abnormal (Score = 0)
Fetal breathing movements	1 or more episodes of >20s within 30 min	Absent or no episode of >20s within 30 min
Gross body movements	2 or more discrete body/limb movements within 30 min (episodes of active continuous movement considered as a single movement)	<2 episodes of body/limb movements within 30 min
Fetal tone	1 or more episodes of active extension with return to flexion of fetal limb(s) or trunk (opening and closing of hand considered normal tone)	Slow extension with return to partial flexion, movement of limb in full extension, absent fetal movement, or partially open fetal hand
Reactive FHR	2 or more episodes of acceleration of >15 bmp* and of >15 s associated with fetal movement within 20 min	1 or more episodes of acceleration of fetal heart rate or acceleration of <15 bmp within 20 min
Qualitative AFV	1 or more pockets of fluid measuring >2 cm in vertical axis	Either no pockets or largest pocket <2 cm in vertical axis

*Beats per minute