Biophysical profile scoring

  The fetal biophysical profile (BPP) is a test performed to measure fetal well-being. It uses ultrasonography to measure fetal breathing, fetal movement, fetal tone, and amniotic fluid volume. A non-stress test is done to assess fetal heart rate. Each of these five variables is given a score of zero or two, for a potential total score of ten.

Purpose

The purpose of the BPP is to assess fetal well-being. It is a tool used near or at term by clinicians to assess the potential risk of fetal compromise or demise due to fetal hypoxia or acidosis. Intervention such as maternal hospitalization, or delivery may follow a BPP score of four or below.

Precautions

A reliable BPP score necessitates that a well-trained ultrasonographer perform the test. However, fetal parameters are recorded over a 30-minute time period, with an additional 30 minutes for the non-stress test (NST) component. Information on a very active fetus is obtained inconsiderably less time. The complete BPP can therefore be a time-consuming test. The NST records the relationship of fetal heart rate to fetal movement. It is associated, however, with a false-positive rate as high as 80%, and averaging about 50%.

Description

The BPP is a test scoring five fetal vital sign variables: fetal heart rate, fetal breathing, fetal movement, fetal tone, and amniotic fluid volume. An ultrasound is used to visualize the fetus to measure these variables. The fetal heart rate is assessed through an NST. Each parameter is given a score of two or zero, based on specific criteria. The total potential score is a 10. The BPP may be ordered following a non-reactive NST; after a suspicious oxytocin challenge/contraction stress test (CST); or after term, especially if there is concern about low amniotic fluid volume (oligohydramnios). The first researchers to report the results of scoring these fetal biophysical variables as a group were Manning and colleagues in 1980.

Fetal breathing (FB) is measured by watching for movement of the fetal thorax and diaphragm. This is to assure breathing, and not just chest wall movement. A score of two is given if at least one occurrence of FB lasting at least 30 seconds during the 30-minute test is noted. A score of zero is given if no FB is seen, or if the FB lasted less than 30 seconds.

Fetal movement is defined by gross arm, leg, or body activity. A score of two is given if there are at least three separate limb/body movements during the 30-minute test. A score of 0 is given if there are two or fewer limb/body movements during the test. Facial movement is not scored.

Fetal tone is defined by active extension and flexion of the fetal limbs, trunk, or hand; or if the hand remains in a flexed position during the entire 30-minute test. A score of two is given if the hand and fingers are seen to fully extend and flex into a fist. A score of zero is given if no such movement is recorded, or with slow or partial flexion or extension.

Amniotic fluid volume is estimated for sufficiency. Since fetal anatomic structures do not allow full visualization of all the amniotic fluid, it is estimated by measuring pockets of fluid from 0.39 to 0.78 in (1 to 2 cm) in height on ultrasound. A score of two is given if at least one pocket of fluid measures 0.78 in (2 cm) or more in height. A score of zero is given when no such pockets can be measured. Normal amniotic fluid volume peaks at about 750 ml at 32 weeks gestation, stays stable until term at 40 weeks, and then declines to about 400 ml by 42 weeks. Excessive amniotic fluid amounts (hydramnios), such as might be seen in diabetic mothers, may be as high as 1700 to 1900 ml. Oligohydramnios is defined by about 300 ml of fluid volume. The amniotic fluid is produced as the fetus urinates and through lung secretions. The volume is controlled by fetal swallowing and by reabsorption through the membranes. The amniotic fluid index (AFI) is also used to determine sufficiency of amniotic fluid. In this method, the largest vertical column of fluid in each of the four uterine quadrants is measured. Because of the role of the fetus in the production and control of amniotic fluid, it is one variable in fetal wellbeing assessment.

Fetal heart rate (FHR) variability is measured during a NST. The fetal heart rate is normally variable in nature. Accelerations, or increases in FHR, are usually seen in response to fetal movements and are therefore reassuring. A score of two is given for two or more accelerations of at least 15 beats per minute that last at least 15 seconds each during a 30-minute period. A score of 0 is given if fewer than two accelerations are seen within 30 minutes