Chapter 6. Biophysical Profile

Welcome to the Biophysical Profile chapter. This widely used antenatal test is a primary tool for monitoring fetal well-being. Indications, techniques, scoring, and clinical management are presented. The biophysical profile (BPP) falls within point-of-care ultrasound practices. The ultimate purpose of the BPP is to prevent stillbirth.

OBJECTIVES:

By the completion of this Section the participant will be able to:

1. Know the indications for performing BPP as a part of antenatal surveillance

2. Know the numeric criteria for all 4 components of the BPP, and the clinical implications of scoring totals

3. Describe common pitfalls in measuring AFI

4. Define a modified BPP

5. Discuss basic clinical management of women with abnormal BPP scores

The biophysical profile (BPP) monitors high-risk pregnancies for potential fetal complications. Certain maternal, fetal, or obstetric factors can raise the risk from twice as high to up to 40 times greater than the 5 per 1,000 rate seen in low-risk pregnancies.

Goals of the Biophysical Profile (BPP)

Figure 1. Goals of the biophysical profile.

The American College of Radiology issued recommendations based on extensive review of evidence in 2016 and concluded that since there is limited evidence that antepartum testing decreases the risk of fetal death, testing is not recommended in low-risk pregnancies. However, women with high risk factors for stillbirth should have antenatal testing. No single testing modality is superior to another since all have relatively high negative predictive values. Testing must be individualized for the particular clinical condition and risk for stillbirth.¹

Figure 2. Indications for outpatient fetal surveillance, including the biophysical profile.

A BPP is commonly performed due to potential compromises in placental function from maternal complications, oligohydramnios, or decreased fetal movement. Fetal growth restriction often results from reduced placental perfusion. Previous unexplained fetal demise increases monitoring vigilance, and monochorionic multiple gestation presents risks since both fetuses share one placental circulation.

ACOG and SMFM recommendations for performing antenatal testing (factors associated with increased risk of stillbirth and strategy for surveillance after viability. These are not designed to be mandates, but present guidelines for identifying those at greater risk.²

Condition	Weeks of gestation to begin	Frequency
Pre-pregnancy BMI 35-40	37	weekly
Pre-pregnancy BMI >40	34	weekly
Maternal age older than 35 years	Individualized	individualized
Previous stillbirth before 32 wks	Individualized	Individualized
Previous stillbirth at or after 32 wks	32	once or twice weekly
History of other adverse pregnancy outcomes in preceding pregnancy --Previous growth restriction requiring preterm delivery --Previous preeclampsia requiring preterm delivery	32	weekly
Cholestasis	At diagnosis	once or twice weekly
Late term (postdates)	41	once or twice weekly
Chronic placental abruption	At diagnosis	once or twice weekly
Vasa previa	Individualized	individualized
Velamentous cord insertion	36	weekly
Single umbilical artery	36	weekly
Isolated oligohydramnios	At diagnosis	once or twice weekly
Polyhydramnios (mod to severe)	32-34	once or twice weekly
Fetal growth restriction	At diagnosis	once or twice weekly
Decreased fetal movement	At diagnosis	once
Twins uncomplicated	36	weekly
Twins dichorionic, with maternal complications	At diagnosis	Individualized
Twins uncomplicated Mono-Di	32	weekly
Twins complicated	Individualized	Individualized
Twins monoamniotic	Individualized	Individualized
Fetal anomalies	Individualized	Individualized

Table 1. Specific indications for antenatal testing (ACOG and SMFM)

Conditions: Maternal	Weeks of gestation to begin	Frequency
Hypertension, chronic	32	weekly
Hypertension, poorly controlled	At diagnosis	Individualized
Gestational hypertension/preeclampsia Without severe features	At diagnosis	twice weekly
Gestational hypertension/preeclampsia WITH severe features	At diagnosis	daily
Diabetes – gestational, controlled	32	once or twice weekly
Diabetes – gestational, poorly controlled	32	twice weekly
Diabetes – pregestational	32	twice weekly
Lupus - uncomplicated	32	weekly
Lupus – complicated	At diagnosis	twice weekly
Sickle cell disease - uncomplicated	32	once or twice weekly
Sickle cell disease – complicated	At diagnosis	individualized
Other hemoglobinopathies	Individualized	Individualized
Renal disease (Cr greater than 1.4 mg/dl)	Individualized	Individualized
In Vitro fertilization	36	weekly
Substance abuse (alcohol, 5 or more drinks per week)	36	weekly

Table 2. Specific maternal indications for antenatal testing (ACOG and SMFM).

When to start testing

Figure 3. When to start antenatal testing.

Biophysical profile testing typically begins at 32 weeks or at the earliest point when neonatal survival is possible in cases of severe fetal compromise. Although some may conduct BPP earlier if all indicators are present, it is generally considered most reliable starting at 32 weeks.

Biophysical profiles are usually done weekly but may be performed more often if risk is higher. Some providers alternate BPPs with nonstress tests every three days to ensure frequent fetal evaluation.

The Biophysical Profile consists of 2 components:

1. Electronic fetal monitoring (sometimes called CTG, or cardiotocography in countries outside of the United States) with the specific protocol known as Nonstress Testing (NST).

2. Ultrasound components .

Each component is scored and added together to determine total score.

The MODIFIED biophysical profile consists of only the ultrasound component, and is used in many settings alternating with the NST.

Some practice now use simply amniotic fluid index and NST together.

This chapter will focus on the ultrasound component only.

Xx components

The 4 major components of a BPP assessed by ultrasound:³

1) Amniotic fluid, sometimes called the amniotic fluid index or AFI

2) Fetal breathing movements

3) Fetal Tone

4) Fetal Movement

Figure 4. The four components of a biophysical profile.

Table 3 details the scoring system used for the BPP assessment. Each of the four sections assessed by ultrasound receives either a score of 2 (if the parameter is present as defined), or 0 if it is not. There are no values assigned to odd numbers – only even numbers (2 or 0). The possible total scores are 2, 4, 6, or 8, with 8 being the highest score. Including a non-stress fetal monitoring test can add an additional 2 points if the result meets criteria, making the maximum possible total score 10 out of 10.

Normal scores are defined as 8 out of 8, or 8-10 out of 10 if the non-stress test (NST) is included.

Further details will be provided in the following text and figures.

Table 3. Components, descriptions and scoring of the biophysical profile.

Amniotic Fluid

Amniotic fluid was once thought to be simply an environment for the fetus to allow for growth and movement, but more recently it is known as a complex and dynamic system. Its presence and amount are correlated with fetal and maternal conditions.⁴

Amniotic fluid in the second half of pregnancy is affected by pulmonary excretion, fetal urine production, and fetal swallowing

Figure 5, Images 1, 2. Description and image examples of measuring a fluid pocket.

Amniotic fluid volume (AFV), also known as the Amniotic Fluid Index (AFI), can be measured in two ways. One method is to measure the single deepest pocket of fluid in the uterus, excluding fetal parts or the umbilical cord. This involves scanning all uterine quadrants to find the largest pocket.

The 4-Quadrant AFI method measures the depth of fluid in four pockets, one from each quadrant, then adding together for a total. Consistent technique is crucial to avoid measurement variance, so technique will be presented. The top of each measured pocket should be either the anterior uterine wall or the placenta if it is positioned anteriorly.

Figure 4. Photo of correct and incorrect ways to hold a transabdominal transducer to measure fluid pockets.

To measure fluid in a pocket, the transducer must be held in the sagittal plan; not transverse or angled in any way.

Measuring the 4 quadrant AFI

Divide the abdomen into right, left, upper, and lower halves at the umbilicus to view all four uterine quadrants. Scan each quadrant by moving up and down to locate fluid pockets but keep the transducer straight along the sagittal axis without angling it.

Figure 5. Illustration of how to position the transabdominal transducer in measuring the 4 maternal abdominal quadrants in fluid measurement.

The following diagrams (Figures 6 and 7) demonstrate how NOT to hold the transducer.

Figure 6. Illustration of incorrect ways to place the transabdominal transducer while measuring fluid pockets.

A – the transducer is angled and not in a vertical position

B – is at the intersection of 2 quadrants, creating the potential of measuring the same pocket in those region 2 times

C – is probably too low. Sometimes there is a pocket of fluid that is midline, between the fetal head and the cervix, but this pocket should not be measured.

D – transducer is too far lateral, making it less likely to locate a pocket without angling the transducer inward, causing the measurement to be inaccurate.

It is recommended to maintain the transducer perpendicular to the floor rather than at an angle. Applying excessive pressure to the transducer may decrease the volume of the pocket.

Figure 7. Illustration of incorrect ways of approaching the fluid pocket while measuring fluid pockets.

There are 3 conditions that are found when measuring amniotic fluid index:

Figure 8. Definitions of normal, low (oligoohydramnios) and elevate (polyhydramnios) fluid.

Normal (5-24cm total AFI)

Oligohydramnios (less than 5 cm total AFI)

Polyhydramnios (25 or greater cm total AFI)

Figure 9, Images 1, 2, 3, 4. Images to illustrate correct measurement of a 4-quadrant AFI, and the total indicated by the red arrow.

While measuring, the machine’s computer usually sums the measurements for each quadrant and provides a total (see red arrow). If no fluid is seen in a pocket, skip it or record zero (see green arrow).

Figure 10, Image 5. Guideline for avoiding measurement of a thin pocket.

Another guideline to follow is to exclude the measurement of any pocket with a width less than 1 cm, regardless of its depth.

Pitfalls of measuring AFI

Certain challenges must be addressed when measuring AFI. In this image, the measurement indicated by the white dotted line is inaccurate because it does not extend to the uterine wall. The image illustrates a measurement taken from the reverberation artifact downward, resulting in an underestimation of the true value.

Figure 11, Image 6. Pitfalls in measuring amniotic fluid.

Some other pitfalls are:

Excessive pressure on the transducer, causing the measurement to be shallower.

Ensure that the measurement line is drawn straight down rather than at an angle. Drawing at an angle will result in a measurement that exceeds the actual size of the pocket and does not comply with established guidelines.

Figure 12, Images 7, 8. Additional pitfalls in measuring amniotic fluid.

A 4-quadrant AFI can be captured on a single screen with some ultrasound machines, while others require separate images for each quadrant.

Images 9, 10, 11, 12. Images illustrating a correctly measured AFI.

Most experts require that any fluid pocket be free of any fetal part or umbilical cord. Applying color flow to the view of a fluid pocket provides proof that the cord was not present. There are some perinatologists no longer recommending the exclusion of pockets including cord. Check local guidelines or protocols in your institution. If a cord loop or fetal part is seen, measure away from them or to the side of the structure.

Images 13, 14. Images depicting the use of color flow to identify umbilical cord to avoid inclusion in the fluid pocket measurement.

Maximum vertical pocket (MVP)

The term "maximum vertical pocket" (MVP) refers to the single deepest pocket. It may also be called the "deepest vertical pocket" (DVP), both of which have the same meaning.

Refer to the table in Figure 13 (below) for parameters: a single pocket less than 2 cm suggests oligohydramnios, while a 2–8 cm deepest pocket is considered normal regardless of other pocket sizes.

A single pocket measuring more than 8 cm may indicate polyhydramnios; however, a 4-quadrant AFI is recommended for confirmation, as additional pockets may be smaller and result in a normal total 4-quadrant volume. DVP is considered less reliable for assessing polyhydramnios compared to oligohydramnios.

Figure 13. Definition of oligohydramnios, normal fluid, and polyhydramnios by AFI measurements.

Oligohydramnios

The more concerning problem in terms of fetal outcomes related to fluid level is oligohydramnios. Causes of oligohydramnios are:

Fetal demise or medications

Fetal Renal abnormalities

Intrauterine growth retardation

Premature rupture of membranes or preterm premature rupture of membranes

Postdates

Chromosomal abnormalities (usually noted in second trimester rather than later)

Figure 14. Causes of oligohydramnios

The overall incidence of oligohydramnios ranges from approximately 0.5% to 6% of all pregnancies. Diagnostic criteria include an amniotic fluid index (AFI) of 5 cm or less, which correlates to an estimated fluid volume below 500 mL, or identification of a single deepest vertical pocket measuring less than 2 cm.

Oligohydramnios early in pregnancy suggests reduced fetal kidney output and a poor prognosis.

Figure 15. Diagram of oligohydramnios descriptors.

Oligohydramnios, or reduced amniotic fluid, is sometimes suspected when there is difficulty obtaining clear visualization of anatomical structures in the uterus, making assessment more challenging. If fetal parts are unclear or “fuzzy” when scanning, this may indicate low fluid. Some radiologists or sonologists may describe fluid as “subjectively low fluid,” and this is acceptable. However, non-specialists should provide actual measurements rather than making qualitative assessments.

Images 15, 16, 17. Images depicting the “cloudy” views of fetal parts due to low fluid, often a first indication of low fluid.

ecommended management of oligohydramnios

The American College of Obstetricians and Gynecologists notes that fetal surveillance tests often yield high false-positive rates and low positive predictive values.⁵ Abnormal results typically lead to further testing or delivery, depending on test outcomes, maternal and fetal condition, and gestational age. Because there can be subjective evaluation while performing a BPP, it is essential that technique is observed to minimize inappropriate clinical decisions based on the scores obtained.

Clinical management may vary depending on the clinical situation. A BPP score of 4 typically indicates the need for imminent delivery. For growth-restricted infants with this score, delivery may be considered at or after 37.0 weeks. A secondary assessment is Doppler evaluation is usually performed in the case of a low BPP, to confirm fetal compromise.

Figure 16. Recommended management guidelines per ACOG 2021.⁶

GENERAL RECOMMENDATIONS: Abnormal results from a non-stress test (NST) or modified biophysical profile (BPP) should typically be followed by further evaluation, such as a contraction stress test (CST) or a complete BPP. In the absence of obstetric contraindications, induction of labor (IOL) with continuous fetal monitoring may be considered for delivery in the setting of abnormal test results. The management of oligohydramnios is best approached in a stepwise and systematic manner.

Figure 17. Recognized criteria and management of oligohydramnios.⁶

For managing oligohydramnios, using SDP or DVP rather than AFI is recommended, as it leads to fewer unnecessary interventions. It should be noted, however, that one must view all quadrants to determine which pocket is the lowest. If low fluid is caused by ruptured membranes, management should focus on the membrane status rather than placental function. If oligohydramnios persists or worsens, deliver the baby at 36-37 weeks.⁴

Polyhydramnios

Polyhydramnios, the opposite of oligohydramnios, is excess amniotic fluid. On ultrasound, this appears as large fluid pockets around the baby. Fetal features are noted to be very clear and distinct. If seen in second trimester, polyhydramnios may indicate a trisomy, so timely evaluation is important. If polyhydramnios is seen near term, there is a risk of cord prolapse if membranes rupture spontaneously.

Figure 18, Image 18. Definition and image demonstrating polyhydramnios.

Polyhydramnios may be classified as mild, moderate, or severe based on its quantitative assessment. When polyhydramnios is identified, consultation with an advanced provider is recommended.

Table 4. Measurement parameters for degrees of polyhydramnios.

Image 18 shows a 9.53 cm fluid pocket. By SDP criteria, this suggests polyhydramnios, requiring further evaluation. However, if the other three pockets total less than 5 cm, the AFI would be 14.5 cm, which is normal. This demonstrates that the 4-Quadrant AFI is a more reliable method for diagnosing polyhydramnios than DVP.

Image 18. Image illustrating a large DVP (greater than 8 cm).

The images below (images 19-22) display a high-normal fluid level (24.75cm). Polyhydramnios is defined by an AFI of 25 or higher; however, it also applies here because the deepest pocket in quadrant 2 measures 8.25cm, exceeding the threshold of 8cm. Thus, both criteria for polyhydramnios are met.

Images 19, 20, 21, 22. Images depicting mild polyhydramnios, with total AFI of 24.75 (greater than 24).

Fetal breathing movements

Fetal breathing movement indicates good fetal health. To assess this, identify the diaphragm and observe rib movement during breathing. Standard criteria require at least 30 seconds of continuous fetal breathing, though recent studies show that shorter, intermittent breaths (5–10 seconds) with pauses may also be normal.

Image 23. Image of sagittal view of fetus identifying diaphragm to observe for fetal breathing movements.

The video clips below illustrates fetal breathing by depicting the diaphragm's vertical movement in relation to the ribs. To play the video clip, position the cursor at the lower edge of the image and select the white arrow.

xx fetal breathing clip 1 (need MP4)

Xx fetal breathing clip 2 (need MP4)

Image 24 shows an alternative method of observing fetal breathing movementby placing color flow near the baby’s nostrils; movement of fluid in and out will be visible if the baby is actively moving fluid in and out.

Image 24. Image of color flow from fetal nostril, demonstrating flow of fluid in and out of nose (indicative of fetal breathing movement)

Xx single movement no breathing (video clip) need MP4

This video shows slight movement but no clear fetal breathing. Distinguishing between maternal and fetal breathing is essential. The fetal heartbeat can also mimic diaphragmatic movement. To play the clip, click the white arrow at the bottom edge of the image.

Fetal tone

Fetal tone refers to the movement of a baby's limbs, either by flexing or extending them. A score of 2 (adequate) is given when at least one episode of flexion or extension is observed. If only slow extension occurs, or no flexion is noted, a score of zero is assigned.

Figure 19. Fetal TONE criteria for BPP.

Xx Fetal hand extension clip (need MP4)

This video illustrates the movements of fetal hand flexion and extension. To play the clip, position your cursor at the lower edge of the image and click the white arrow.

Fetal movement

Fetal movement is easy to observe and often apparent while checking other parameters. A single episode of limb flexion (for tone) also qualifies as one of the required three fetal movements. Since babies can sleep for up to 30 to 40 minutes, wait the full duration before concluding inadequate movement.

Figure 20. Fetal MOVEMENT criteria for BPP.

BPP report

This document serves as a standard BPP report, detailing measurements for all four quadrants with a comprehensive AFI value. The report should also include fetal heart rate, fetal presentation, placental location, and scores for each BPP parameter. Furthermore, annotations must specify the individual performing the scan and provide any relevant additional comments.

Figure 21. Example of normal BPP report.

Abnormal BPP report

Figure 22 presents an example of an abnormal BPP performed in conjunction with a growth ultrasound. Fluid level is normal at 14.86 cm (4 quadrants), and the fetal heart rate is also normal at 154. The second page of the report lists the BPP scores.

Fetal movement – 0

Fetal breathing -0

Movements – 2

Fetal Tone – 0

AFI – 2

For a total of 4 out of 8.

Comments included remarks that this baby was observed for the full 30 minutes, without meeting the criteria for a normal fetus, and that the plan was for the woman to see the midwife that day for further clinical management.

Figure 22. Example of abnormal BPP report.

SUMMARY

--Women and fetuses with risk factors for adverse outcomes can benefit from increased surveillance using the method of biophysical profile testing.

--Modified BPP includes 4 parameters, each achieving a score of either absent or present (0 or 2 respectively), for a total ideal score of 8/8 possible points. If NST is included in the testing, a reactive NST would yield another score of 2, making the total score 10/10.

Amniotic fluid index

Fetal breathing movements

Fetal tone

Fetal movement

--Any score of less than 6/8 warrants further testing and a score of less than 4 warrants immediate referral for urgent high-risk management.

--BPP can be used in conjunction with other fetal testing methods such as CTG or EFM (electronic fetal monitoring – either nonstress or contraction stress testing)

Women's Point-of-Care Ultrasound: Second and Third Trimester

Biophysical Profile