FETAL BIOPHYSICAL PROFILE

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The development of objective clinical methods for the detection of the fetus at risk for death or damage in utero did not begin in earnest until the past few decades. At its inception, objective fetal biophysical testing was limited to a single variable, the fetal heart rate, and antepartum testing methods, including the oxytocin challenge test and its variants such as the spontaneous contraction stress test (CST), were extrapolated from intrapartum observation.30, 34 Almost from the outset of antepartum fetal heart rate monitoring, it was recognized that the record contained important information even in the absence of uterine contraction responses. Specifically, the association of fetal movement at heart rate acceleration, the basis of the nonstress test (NST), was recognized to be of prognostic value.9

At around the same time, Dawes and colleagues6 were able to demonstrate an exquisite sensitivity of the fetal respiratory center to experimental hypoxemia in a series of elegant experiments in the chronic fetal lamb preparation, raising interest in the potential of this measurement in predicting human fetal compromise. By the mid 1990s, the revolutionary clinical tool of dynamic real-time B-mode ultrasound became available, and, through this method, observation of a broad range of dynamic fetal biophysical activities became a clinical reality. From the nascence of this new clinical testing modality, it was evident that observation of the presence or absence of breathing movements in the human fetus was as predictive as the NST,12 was useful in the differentiation of true-positive and false-positive CST results,13 and, when combined with the heart rate test, yielded a better prediction of the risk of fetal death or compromise than any single test.14 Furthermore, it became evident that objective recording of gross body movements was predictive of fetal health and disease,15 and that when this information was combined with other biophysical variables, predicative accuracy was improved. The preliminary observations provided a first insight into a fundamental tenet of antepartum risk assessment, that is, the predictive accuracy of fetal testing methods improves as more fetal variables are considered. From these observations, the new concept of composite fetal assessment arose. The fetal biophysical profile scoring (BPS) method emerged from this rich clinical milieu as a means of integration of dynamic biophysical activities into a workable clinical format.16

This article reviews the clinical role of the fetal BPS in the prediction and prevention of perinatal mortality and perinatal morbidity as reflected by antenatal acidosis, immediate neonatal compromise, and long-term sequelae. Application of the testing method to discrete at-risk pregnancy categories is described.

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THEORETIC BASIS OF THE FETAL BIOPHYSICAL PROFILE

The fetal central nervous system initiates and regulates fetal biophysical activity by the production of efferent nervous traffic that originates in specialized centers throughout the brain and travels via the peripheral nerve network to the effector apparatus in the periphery. Thus, the muscles that control fetal movement, tone, and breathing may be viewed as transducers of the central signal source—the brain. Interruption of the supply of oxygen to neuronal tissue results in a cessation of

METHOD FOR FETAL BIOPHYSICAL PROFILE SCORE

The BPS is constructed from data obtained from two sources: (1) the results of observation by a dynamic ultrasound method of the presence or absence of fetal breathing movements, gross body movements, tone, and amniotic fluid volume; and (2) the results of the fetal heart rate responses to fetal movements as recorded using an external method of continuous fetal heart rate recording (Table 1). Although there is no theoretical reason to order these two observations in any particular way, there is

WHEN TO START TESTING

Two general clinical guidelines are followed in determining when to begin antepartum BPS surveillance in the high-risk fetus. First, testing should not be instituted until active intervention for fetal compromise is possible. Initially, fetal BPS was used as a method for the detection of fetal asphyxia. When abnormal results were encountered, the recommended action was delivery. The degree of abnormality of the score necessary to trigger this response varied by gestational age such that the

FREQUENCY OF TESTING

The frequency of testing should be based on the clinical circumstances for each individual case and can be expected to vary widely between and even within cases. The usual starting point is to plan for a testing frequency of once per week in most referred high-risk pregnancies and at least twice per week in the pregnancy at or beyond 294 completed days (>42 weeks) and in the insulin-dependent diabetic pregnancy. The testing frequency should be adapted to the clinical situation. The more

CLINICAL MANAGEMENT BASED ON THE TEST SCORE

The goal of antepartum fetal assessment is not to treat the test result but rather to treat the fetus and mother. Accordingly, clinical management based on BPS results must include a consideration of the full spectrum of maternal and fetal clinical information (Tables 2 and 3).

In general, a normal BPS (defined as 10/10, 8/10 with normal amniotic fluid, or 8/8 without NST) may be interpreted as reliable evidence that the fetus is not compromised at the time of testing. A normal BPS is also a

Selective Use of the Nonstress Test: Biophysical Profile Score of 8/8

In the early clinical application of fetal BPS in referred high-risk pregnancies, it became evident that when the four dynamic ultrasound variables were normal, the probability of encountering an abnormal (nonreactive) NST was exceedingly small.16 Furthermore, the test accuracy parameters of the four ultrasound-monitored variables when normal (BPP 8/8, no NST) were identical to that reported for the normal fetal BPP score (BPP 10/10, NST included).18 In contrast, when one or more of the

BIOPHYSICAL PROFILE SCORE AND FETAL CORD BLOOD ACID-BASE AND pH VALUES

The relationship between the BPS and fetal blood gas and pH has been studied in several clinical settings. A highly significant direct linear correlation has been reported between the BPS and cord blood obtained at delivery.20, 23, 36 Vintzileos and associates36 compared cord blood gas and pH values with the BPS results in samples collected at cesarean section before the onset of labor in 124 patients and reported a highly significant direct linear correlation with both arterial and venous pH.

CLINICAL APPLICATION, PREDICTIVE ACCURACY, AND IMPACT ON OUTCOME OF FETAL BIOPHYSICAL PROFILE SCORING

Fetal BPS is used to predict the presence or absence of fetal asphyxia. Both the gestational age at which testing is begun and the testing frequency vary according to maternal and fetal risk factors. In general, testing is not begun at a gestational age before which intervention for fetal reasons is contemplated. This age varies among centers. At the author's facility, testing is not started before 26 weeks' gestation, except in clinical circumstances in which fetal therapy is possible (e.g.,

BIOPHYSICAL PROFILE AND CEREBRAL PALSY

Cerebral palsy is defined as a nonprogressive neurologic abnormality affecting the regulation of muscles controlling posture, tone, and voluntary movements. The disorder occurs as a result of an insult in the perinatal period. Perinatal asphyxia in the antepartum, intrapartum, or neonatal period is a recognized cause of cerebral palsy.

Because the BPS predicts the presence or absence of fetal asphyxia, it follows that a relationship may exist between the last BPS result and the risk for cerebral

ADULT SEQUELAE OF FETAL ADAPTATION TO ASPHYXIA: THE ALPHA-OMEGA CONCEPT

The fetus is superbly adapted to its intrauterine environment. Remarkable adaptation mechanisms allow the fetus to cope and survive with asphyxia, at least in the short term, and usually for a sufficient time to trigger parturition. Two of these adaptive compensatory responses— the cessation of all nonessential acute biophysical activities and the redistribution of cardiac output away from nonessential organs to life-essential fetal organs (i.e., placenta, heart, brain, and adrenals)—form the

References (37)

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Address reprint requests to Frank A. Manning, MD, Department of Obstetrics and Gynecology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Belfer Room 512, Bronx, NY 10461

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Department of Obstetrics and Gynecology, Albert Einstein College of Medicine, Bronx, New York

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