Fetal Biophysical Profile
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 10.
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.
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%.
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
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.
Because the BPP is done during the third trimester of pregnancy, there is sufficient amniotic fluid to provide contrast to clearly visualize the fetus. No preparation is usually required before the test is performed. The mother may be asked to have a snack prior to the test to encourage a more active fetus. Because the mother's abdomen is exposed, curtains or a closed door should provide privacy. A comfortable room air temperature and the warming of the transducer gel can assist in putting the mother at ease. The mother should be asked if she wants her partner or support person with her during the test. A towel or cloth should cover the mother's clothing to avoid its getting wet from the transducer gel.
The BPP uses an external transducer to visualize the fetus and the amount of amniotic fluid. A towel or cloth can be used to wipe off excess gel and dry the abdomen after the test. In the event that test results indicate fetal compromise, a health care professional should remain with the mother to provide emotional support and answer questions as needed.
Because the test is noninvasive in nature, complications from the test itself are unexpected. A non-reassuring test may be repeated four to 24 hours later for comparison. Efforts should be made to assess for false negatives or false positives. A low BPP score may be followed by interventions with their own potential complications.
A score of eight or ten out of ten provides a reassuring BPP score. If the score is eight, with a decrease in amniotic fluid volume, delivery may be indicated, with fetal maturity. A score of six arouses suspicions of chronic fetal hypoxia. A repeat test within four to six hours may be ordered. Delivery may be indicated if there is a reduction in the amniotic fluid volume. A score of four is
Fetal demise—The death of the fetus in utero.
Transducer—The external device or probe used in conjunction with the ultrasound machine. Applied on the outside of the abdomen with a special gel, it bounces sound waves into the area being visualized, and then sends the return waves back to the computerized ultrasound machine for interpretation and visualization on the monitor.
Variability—The fetal heart rate is expected to change, or be variable in nature. While the adult heart rate remains stable, except with exertion, the rate of the fetal heart continually moves up and down. A flat fetal heart rate is considered an ominous sign.
suspicious of chronic fetal hypoxia. A fetal lung maturity test may be done to assess readiness for delivery. Delivery is indicated if a repeat BPP after 24 hours confirms a score of four or below. A score of zero to two elicits a strong suspicion of chronic fetal hypoxia. The BPP testing period may continue for two hours instead of the usual 30 minutes. If the two-hour score is four or below, delivery is indicated if the fetus has a good chance at extrauterine survival.
Health care team roles
The BPP should be performed by a trained ultrasonographer. The NST may be performed by a nurse or a radiology technician in the antenatal division of an obstetric department, in the radiology department, or in an obstetric office. As with any test, patient anxiety is heightened with concerns of fetal compromise. Therefore, the ability of the health care professional to convey accurate information in a calming manner is very important.
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