Basic Obstetric POCUS

Chapter 11. 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 practice. The ultimate purpose of the BPP is to detect fetal compromise and 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

Goal of the Biophysical Profile

The biophysical profile (BPP) monitors pregnancies at risk for 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.

Figure 1. Goal of Biophysical Profile

Figure 2. Indications for monitoring fetal well being

The BPP is commonly performed to monitor 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 the gestation of viability. These are not designed to be mandates, but do give guidelines for identifying those at greater risk.

The following tables (table 1 and table 2) below outline all the conditions for which BPP is recommended by experts in the United States. You do not need to memorize this - but be familiar with the types of complications that would be most likely to affect fetal well-being.

Table 1. Conditions and recommendations for performing antenatal testing

Table 2. Maternal conditions and recommendations for antenatal testing

When to start testing

The above lists in Tables 1 and 2 of conditions for recommended testing gives various gestational ages for starting the testing. In general, most OB providers begin antenatal testing (BPP) at around 32 weeks. It can be done earlier for higher risk pregnancies, but use 32 weeks as your guideline for the women you are most likely to see. A condition requiring earlier testing should be managed by a higher level obstetric provider.

The other thing to note is that starting to test at the “earliest time for prognosis of neonatal survival” depends on the level of advanced neonatal care available to the women in your area. In a hospital with neonatologists and a high level neonatal intensive care unit, the age of viability may be as early as 23-24 weeks gestation. If you are in an area with fewer resources, the age of survivability would likely be much later in gestation.

Figure 3. When to start 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.

Antepartum testing, essentially meaning 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). This technology is not generally used in your area, so ultrasound becomes the testing of choice.

2. Ultrasound components

This chapter will focus on the ultrasound component only.

When performing the BPP, each component is scored and combined together to determine total score.

Figure 4. Components of the BPP

The 4 major components of a BPP assessed by ultrasound: Amniotic fluid, sometimes called the amniotic fluid index or AFI

1) Fetal breathing movements

2) Fetal Tone

3) Fetal Movement

You may hear the term “MODIFIED biophysical profile”. This consists of ultrasound measurement of fluid pockets and adding the Nonstress test with electronic fetal monitoring. Since you are not using electronic fetal monitoring, this will not be an option for your practice.

Figure 5. Table of BPP components and scoring parameters

Figure 5 above provides additional detail on how to score each of the parameters. 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 in between– only even numbers (2 or 0). The parameter is either present, or it is not. The possible total scores are 2, 4, 6, or 8, with 8 being the highest score.

Normal scores are defined as 8 out of 8 for an ultrasound BPP only.

Amniotic Fluid

Amniotic fluid measurement is the first parameter to be described.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.

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

Figure 6. Amniotic fluid measurement technique

AFI (Amniotic fluid index)

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.

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

Figure 7. Holding the transducer properly for fluid measurement

Figure 8 below illustrates the transducer positions in each of the 4 quadrants of the mother’s abdomen/uterus.

Figure 8. Illustration of dividing the uterus/abdomen into 4 quadrants

Mentally 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.

The diagrams in Figure 9 below demonstrate how NOT to place the transducer.

Figure 9. Illustration of how NOT to position the transducer

Explanation of Figure 9.

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.

Another tip for performing amniotic fluid measurement is to keep the transducer perpendicular to the floor (not angled). It is also important not to put too so much pressure on the abdomen that it compresses the fluid pocket, making it appear smaller and affecting the measurement.

Figure 10. AFI measuring technique

Figure 11. Definitions of abnormal amount of amniotic fluid

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

Normal (5-24cm total AFI)

Oligohydramnios (less than 5 cm total AFI)
Polyhydramnios (25 or greater cm total AFI)

Measurement calculations

When a pocket is identified, start a caliper at the topmost structure and drop it straight down through the fluid pocket to the first structure you encounter. Then hit “measure” on the machine. Be certain you have the setting for AFI to be able to record and tally all of the measurements as you go.

It is not valid to measure a pocket below a fetal structure, even if you see fluid there.

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 12. Measuring 4 quadrants of fluid pockets and adding them for the total

Another guideline to follow is to exclude the measurement of any pocket with a width less than 1 cm, regardless of its depth (see Figure 13 below).

Figure 13. Image of a pocket too thin (width) to consider appropriate to measure.

Figure 14. Pitfalls of measuring fluid

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 15. Additional pitfals of measuring 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 16. Images of 4 quadrant AFI

A 4-quadrant AFI can be captured on one screen with some ultrasound machines that allow for 4 images to display on one screen, while others require a separate image for each quadrant.

When observing fluid pockets, the rule is to exclude any fetal part or cord in the measurement. This requires use of color Doppler each time to be certain you are not including part of the cord in the measured pocket.

Figure 17. Images showing how to confirm the presence of umbilical cord using color Doppler (color flow)

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 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.

Figure 18. Definitions of deepest vertical pocket

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.

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 19. 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 20. Oligohydramnios descriptions

Oligohydramnios, or reduced amniotic fluid, frequently presents as limited 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.

Figure 21. Images showing evidence of low fluid prior to measuring pockets

Because there can be subjective evaluation while performing a BPP, it is essential that technique is carefully followed to minimize inappropriate clinical decisions based on the scores obtained.

Figure 22. Recommended diagnostic criteria for oligohydramnios

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 23. Management recommendations for oligohydramnios

For managing oligohydramnios, using SDP or DVP rather than AFI is recommended, as it leads to fewer unnecessary interventions.

A low fluid level is sometimes seen as a result of rupture of membranes. If this is the case, there is less concern for something ominous like fetal compromise.

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 24. Image showing evidence of increased fluid or 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.

Figure 25. Polyhydramnios categories

Using the DVP or SDP method for determining polyhydramnios

The image in Figure 26 (below) 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.

Figure 26. single deepest pocket

The image in Figure 27 below displays high-normal fluid levels (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.

Figure 27. Images of 4 quad AFI

Fetal breathing

Fetal breathing movement indicates good fetal health. Fetuses need adequate oxygenation from the mother to allow sympathetic and autonomic nervous system function. 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.

Figure 28. Image of how to locate the fetal diaphragm for observing fetal breathing

The video clips below (video 1 and 2) illustrate 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.

Video 1. Clip of fetal breathing

Video 2. Clip 2 of fetal breathing

Fetal breathing can also be demonstrated by 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.

Figure 29. Seeing evidence of fetal breathing by observing fluid movement in and out of nostrils

Video clip 3. Movement of fluid in and out of nostrils

Video clip 4. Slight fetal chest movement without good fetal breathing motions.

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.

Fetal tone

Fetal tone is the third parameter of the BPP, and 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 30. Description of fetal tone

Video clip 5 illustrates the movements of fetal hand flexion and extension which represents good fetal tone.

Video clip 5. Fetal hand extension

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.

A score of 2 is given if there are 3 or more body or limb movements within 30 seconds. A score of zero is given if there are fewer than 3 movements in 30 minutes. There are no in-between scores for partial activity.

Figure 31. Description of fetal movement grading

Video clip 6. Limited fetal movement noted

BPP documentation

Figure 32 shows 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 32. Example of a typical BPP report

Figure 33 below is an abnormal BPP, performed along with a growth ultrasound. The 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

TOTAL: 4 out of 8

A score of less than 6/8 warrants consultation, referral, or scheduled induction of labor, depending on your protocols.

Figure 33. Example of an abnormal BPP report

Comments included remarks that this baby was observed for the full 30 minutes and that the recommendation was for the woman to see the midwife that day for further clinical management. This report demonstrates the critical elements of a BPP report:

indication for the exam
persons performing the exam
individual and total scores
impression
recommended follow up

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.

YOU MAY NOW TAKE THE QUIZ AND MOVE TO THE NEXT CHAPTER. YOU WILL NOT BE ABLE TO OPEN THE NEXT CHAPTER UNTIL YOU COMPLETE AND PASS THE QUIZ. YOU WILL HAVE AS MANY TRIES AS YOU NEED TO GET ALL THE ANSWERS CORRECT!

GULU Midwives Basic Obstetric POCUS

Chapter 11. Biophysical Profile