Point-of-Care Sonographic Evaluation of Fetal Well-Being
One of the most utilized point-of-care sonograms to assess fetal well-being is the biophysical profile (BPP). The BPP is generally performed following a nonreactive nonstress test (NST); although, in some cases, it is the first line of antepartum testing employed in either its full application or with its modified use (the modified BPP). The purpose of this chapter is to describe each component of the sonographic portion of the BPP, along with further description of amniotic fluid assessment.
HISTORY OF THE BIOPHYSICAL PROFILE
The BPP was developed in 1980 by Manning and Associates1 and utilizes traditional electronic fetal monitoring (EFM) in combination with a sonographic fetal evaluation. Manning viewed this technique as “undertaking an intrauterine physical examination, analogous to Apgar scoring.”
As the fetal central nervous system (CNS) matures with advancing gestational age, fetal behavior develops in a specific order. Fetal tone (FT) begins to be evident by ultrasound around 7.5 to 8 weeks of gestation, followed by fetal movement (FM) beginning around 9 weeks’ gestation. Fetal breathing becomes regular at 20 to 21 weeks, followed by development of fetal heart rate (FHR) control (the ability to accelerate and decelerate) at the end of the second or beginning of the third trimester.
With an insidious or chronic loss of fetal oxygenation, the fetus begins to lose these same behaviors, but in the opposite order in which they developed. So, in the event of chronic oxygen deprivation, initially there will be the loss of fetal heart reactivity followed by a decrease or loss of fetal breathing movements (FBM). If the oxygen deprivation continues, a decrease in amniotic fluid will occur. Ultimately, there will be a loss of FM with, finally, the loss of FT.1 Although factors other than deoxygenation may cause a change in some or all of these behaviors, these are the parameters that, when present, were determined to be predictive of fetal oxygenation, and thus they are used as the basis of the BPP.
FHR reactivity, tone, movement, and breathing are CNS activities that respond to acute hypoxic changes. Additionally, decreased amniotic fluid volume (AFV), in the absence of ruptured membranes or fetal renal abnormalities, may be an indicator of chronic fetal compromise as oxygenated blood is shunted from the fetal kidneys to the vital organs. Knowledge of the five parameters, their progressive emergence throughout gestational age, and pattern of decline with increasing hypoxia can provide invaluable information regarding the oxygenation status of the fetus.
The five parameters assessed in the Manning BPP are:
Fetal heart reactivity (the nonstress test)
Fetal tone
Fetal movement
Fetal breathing activity
Amniotic fluid volume
The BPP has a very low false-negative rate, meaning that a score of 8/10 or 10/10 is highly predictive of adequate fetal oxygenation and the absence of fetal metabolic acidemia. However, each single BPP parameter has a high false-positive rate, meaning, for example, that absence of fetal breathing alone may be the result of sleep cycles, medication affects, or some unknown cause other than deoxygenation. The false-positive rate can be greatly reduced when the parameters are combined. The specific criterion for each parameter was defined by Manning with a scoring system of 2 points if the parameter is present and 0 if it is absent (Table 13-1).1,2 There is no partial score.
In 1983, Vintzileos et al.3 proposed a modification to Manning’s scoring system. In addition to Manning’s five parameters, Vintzileos introduced a sixth parameter: placental grading based on the degree of maturation of the placenta. A mature placenta is given the highest score, and the immature
placenta a low score. Additionally, the change to the scoring system for each parameter included adding a middle point value option, a score of 1, that accounted for the observation of partial fetal behaviors, borderline amniotic fluid levels, and/or the inability to grade the placenta (Table 13-2).3
placenta a low score. Additionally, the change to the scoring system for each parameter included adding a middle point value option, a score of 1, that accounted for the observation of partial fetal behaviors, borderline amniotic fluid levels, and/or the inability to grade the placenta (Table 13-2).3
TABLE 13-1 MANNING BIOPHYSICAL PROFILE SCORING SYSTEM | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||||||||
Both forms of BPPs have similar neonatal outcome predictive value. Whichever BPP point system is chosen to be used in a particular health care setting should be clarified and established in a protocol. Potentially, clinical management could be adversely impacted if only a raw score is reported. For instance, a loss of 2 points for oligohydramnios and 2 points for absence of FM would give a score of 8 (out of 12) on the Vintzileos scale and a 6 (out of 10) on Manning’s. In this example, the raw score of eight on the Vintzileos scale would be falsely reassuring if it is believed to be based on the Manning criteria. It is imperative to express the score with both the numerator and denominator (8/12 or 8/10) so that the test may be interpreted correctly. For the purposes of this chapter, the BPP parameters
and scoring system presented will be based on the Manning 10-point criteria.
and scoring system presented will be based on the Manning 10-point criteria.
TABLE 13-2 VINTZILEOS BIOPHYSICAL SCORING SYSTEM | ||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||||||||||||||||||||
 FIGURE 13-1. Reactive nonstress test (NST). |
BIOPHYSICAL PROFILE (BPP) PARAMETERS
Fetal Heart Reactivity
Fetal heart reactivity is determined by performing an NST that is interpreted as reactive or nonreactive (see Chapter 4: Antepartum Assessment). Although the criteria for a reactive pattern may vary among institutions, the most commonly accepted criteria for a reactive NST is the presence of two accelerations within 20 minutes of testing. Each acceleration must last for 15 seconds, with a peak amplitude of 15 beats per minute (bpm) above the baseline FHR (Figure 13-1). The NST is considered nonreactive when it fails to meet the stated criteria for a reactive NST (i.e., fails to demonstrate adequate fetal heart rate accelerations; see Figure 13-2). An additional 20 minutes can be used to evaluate reactivity since it has been well-established that fetal sleep-wake cycles may be up to 40 minutes in length.3,4
A reactive NST is considered one of the best predictors of fetal well-being and the absence of fetal metabolic acidemia. However, a nonreactive NST has a false positive rate of 40% to 80%, meaning that the cause of the nonreactivity may be something other than hypoxia. Therefore, a nonreactive NST needs to be followed by another form of fetal evaluation in order to differentiate the hypoxic from the nonhypoxic fetus. The BPP is the most commonly used follow-up test.4,5
Fetal Tone
FT is the first of the five parameters to develop during fetal CNS maturation. It is defined as the observer witnessing at least one of the following fetal activities: limb extension with return to flexion, flexion/extension of the spine, or the opening and closing of the hand.
Fetal Movement
FM is defined as the observation of flexion and extension of extremities and/or rolling motions of the fetal trunk. Three distinct episodes of FM are required to achieve a full score. Simultaneous movement of more than one body part is counted as a single movement, just as are isolated limb movements.
Fetal Breathing Movements
FBM increase in frequency and duration with advancing gestational age. Ultrasound observation reveals the presence of diaphragmatic and chest wall excursion often best visualized at the level of the diaphragm (Figure 13-3A,B). A minimum of 30 seconds of continuous fetal breathing is required. The presence
or absence of fetal breathing as a reliable indicator of well-being must be evaluated carefully. It is known that breathing movements are sporadic, vary with gestational age, exhibit diurnal variations, and are often absent in the presence of labor. FBMs are known to be reduced in women who have been fasting6 and following glucocorticosteroid administration.7
or absence of fetal breathing as a reliable indicator of well-being must be evaluated carefully. It is known that breathing movements are sporadic, vary with gestational age, exhibit diurnal variations, and are often absent in the presence of labor. FBMs are known to be reduced in women who have been fasting6 and following glucocorticosteroid administration.7
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
