The Uses and Limitations of the Fetal Biophysical Profile

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Objectives of the biophysical profile

The primary objectives of the BPP are to reduce stillbirth and to detect hypoxia early enough to allow delivery in time to avoid permanent fetal damage resulting from fetal asphyxia. Before going into a discussion about the BPP, however, it is important to understand that the efficacy of any fetal surveillance method to prevent fetal death or damage depends on an understanding of the particular pathophysiologic process that leads to neurologic damage or fetal death.5, 6 Kontopoulos and

Technique

Two methods are used in the performance of the BPP. The first is the performance of an NST. This is a continuous FHR tracing. The normal fetal baseline heart rate is 110 to 160 bpm. The NST is considered reactive when there are 2 or more accelerations (a short increase in FHR of >15 bpm, lasting at least 15 seconds) in 20 minutes. For gestations less than 32 weeks, the qualifying criteria for accelerations are greater than 10 bpm, lasting at least 10 seconds. A reactive NST is assigned 2 points

Rationale for the biophysical profile

The fetal BPP is based on the principle that the fetal biophysical activities are controlled by centers in the fetal brain that are sensitive to varying degrees of hypoxia. The presence of a particular biophysical activity is taken as evidence that the center responsible for that activity is intact and has not been subjected to hypoxia and acidosis. The absence of a particular biophysical activity does not necessarily mean that the center is malfunctioning because of fetal compromise, however.

The biophysical score is inversely related to fetal acidosis

Vintzileos and colleagues12 carried out a prospective study on 124 consecutive pregnant women undergoing cesarean deliveries prior to the onset of labor between 26 and 43 weeks of gestation. These investigators performed BPPs on these patients within 6 hours of their cesarean deliveries. They then measured the umbilical cord pH (arterial and venous) immediately after delivery (Fig. 1). They divided the women into 3 groups based on their BPP scores (≤4, 5–7, ≥8). They defined as fetal acidemia

Individual fetal biophysical activities have different sensitivities to fetal hypoxia/acidemia

In a subsequent study, Vintzileos and colleagues14 prospectively studied 62 women undergoing cesarean delivery prior to the onset of labor, performing BPPs within 3 hours of their cesarean deliveries. They correlated the presence and absence of individual fetal biophysical activities with the umbilical cord arterial and venous pH values obtained immediately after delivery. Fetuses with absent breathing or nonreactive NSTs had lower umbilical arterial pH values than those where breathing was

The significance of oligohydramnios

Oligohydramnios is frequently considered a sign of compromised fetal well-being. Oligohydramnios may be associated with impaired uteroplacental blood flow, especially when it is in association with growth restriction. Regardless of the etiology, fetuses in pregnancies complicated by oligohydramnios are at increased risk of adverse perinatal outcomes. The reduced AF volume increases the risk of cord accidents. In a study of 7582 referred patients with high-risk pregnancies with structurally

Placental grading

PL as a component of the BPP has not found widespread acceptance. Vintzileos and colleagues4 found an increased rate of placental abruption and labor complications among patients with grade 3 placentas. A recent study has demonstrated an up to 6-fold increase in adverse perinatal outcomes (including placental abruption, low birth weight, low Apgar score, and perinatal death) among pregnancies where a grade 3 placenta was identified prior to 32 weeks of gestation.17 Thus, even though PL is not

The Biophysical Profile: early studies

In the first prospective study using the BPP for management of 1184 high-risk patients, Manning and colleagues18 found a perinatal mortality rate of 5.06/1000, considerably lower than the rate of 63/1000 in historical controls (a similar high-risk population from the same region the previous year). Baskett and colleagues19 in 1984 published the results of a study where they used the BPP in managing 2400 high-risk pregnancies with 2485 fetuses. They found a perinatal mortality rate of only

The Biophysical Profile: impact on perinatal mortality

Several studies have demonstrated the efficacy of the BPP in reducing perinatal mortality. In a study of 12620 high-risk patients who had 26357 biophysical scores, Manning and colleagues22 found that there were 93 perinatal deaths. Twenty-four of these occurred in structurally normal, nonisoimmunized fetuses (corrected perinatal mortality rate 1.9/1000). Eight of these fetuses died within 7 days of a normal BPP test (corrected false-negative rate of 0.634/1000). The uncorrected stillbirth rate

The modified biophysical profile score (AF and NST)

Because of the excellent sensitivity of fetal NST for fetal acidemia, it has been proposed that this acute marker alone may be used for fetal assessment in combination with the AF volume assessment, a chronic marker. This combination, also known as the modified BPP, has been shown to have excellent false-negative rates that compare with that of the complete BPP.24, 25

The Biophysical Profile and preterm premature rupture of the membranes

The fetal BPP has been used in the assessment and management of pregnancies complicated by PPROM. Vintzileos and colleagues compared BPPs in women with premature rupture of membranes (PROM) with women with intact membranes at gestational ages ranging from 25 to 44 weeks.10, 26 They found no differences in total BPP scores between the 2 groups. They did find a higher frequency of reduced AF volume, reactive NSTs, and absent FBMs, however, in those patients with PROM.10

These same investigators

The Biophysical Profile score and long-term outcomes

There may be some relationship between abnormal BPP scores and long-term neurodevelopmental outcomes. Manning and colleagues,38 using 2 linked databases, attempted to determine if there was any relationship between the last BPP score in women having serial BPPs and the development of cerebral palsy at age 3 years. Of 22,336 high-risk pregnancies, 27 babies later developed cerebral palsy. These investigators found a relationship between last abnormal BPP scores and subsequent development of

Medications and the Biophysical Profile

Several medications used in pregnancy may affect the BPP. These include steroids, β-adrenergic agents, and magnesium sulfate.

Rotmensch and colleagues39 studied 31 women between 27 and 32 weeks of gestation who were receiving 2 doses of betamethasone. They found an approximately 80% to 90% reduction in FBMs over 48 hours as well as a 50% reduction in fetal body movements. FT and AF volume remained stable. Half of all fetuses had a BPP score of 6/8 or 4/8; within 96 hours, however, all BPP scores

Limitations of the biophysical profile

The fetal BPP is a powerful tool in the assessment of fetal health. Yet, it is often misunderstood and misused.46 Perhaps the most important reason that BPP is misused relates to failure to consider the entire clinical scenario.46 For instance, a fetus at term with severe growth restriction should be delivered, despite the presence of a reassuring BPP score.

Among the most common problems is using the total score without any consideration of the individual components.46 For instance, a score of

Suggested algorithm for Biophysical Profile testing

One of the common questions asked about the BPP is when to start testing and with what frequency. The management of a pregnancy where the BPP score is not perfect is also a matter of controversy. Before going further, it is again crucial to emphasize that these cases need to be managed on an individual case-by-case basis. Thus, to answer the first question, the plan of antepartum testing must be appropriate for the individual pregnancy circumstances and the underlying pathophysiologic process.

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