Antepartum fetal assessment using a fetal biophysical profile score

Duration of biophysical profile in periviable and very preterm low-risk pregnancies

BACKGROUND

In recent years, perinatal viability has shifted from 24 to 22 weeks of gestation at many institutions after improvements in survival in neonates delivered at the limit of viability. Monitoring these fetuses is essential because antenatal interventions with resuscitation efforts are available for patients at risk of delivery at the limit of viability. However, fetal monitoring using biophysical profiles has not been extensively studied in very preterm pregnancies, particularly in the periviable period (20 weeks 0 days to 23 weeks 6 days).

OBJECTIVE

This study aimed to (1) investigate whether the completion of biophysical profiles within 30 minutes is feasible in very preterm pregnancies, and (2) determine the average observation time required to achieve a score of 8 out of 8 in very preterm pregnancies from 20 weeks 0 days to 31 weeks 6 days.

STUDY DESIGN

This study prospectively evaluated biophysical scores in singleton pregnancies undergoing routine ultrasonography at or near viability from 20 weeks 0 days to 23 weeks 6 days (periviable or group I), 24 weeks 0 days to 27 weeks 6 days (group II), and 28 weeks 0 days to 31 weeks 6 days (group III). The results and duration of biophysical profiles were compared with those of a control group (32 weeks 0 days to 35 weeks 6 days) undergoing indicated fetal surveillance. Biophysical profiles were performed for all studied pregnancies until a score of 8 out of 8 was obtained. When >1 biophysical profile was obtained during pregnancy, each was analyzed individually. Pregnancies with fetal anomalies or obstetrical/medical indications for fetal well-being surveillance were excluded. Analysis of variance and post hoc Tukey tests were used for comparisons.

RESULTS

Data were collected for 123 participants, yielding 79, 75, and 72 studies for groups I, II, and III, respectively. The control group included 42 patients, yielding 140 studies. At 30 minutes, 80% (63/79) of the studies in the periviable group had a score of 8 out of 8, as opposed to 100% (140/140) in the control group (P<.001). The mean±standard deviation time in minutes to achieve a biophysical score of 8 out of 8 was 23.3±10.1 in the periviable group, as opposed to 9.4±6.5 in controls (P<.001). Extending the study to +2 standard deviations (43.6 minutes) in the periviable group resulted in 97% (77/79) of the scans scoring 8 out of 8 in the absence of adverse outcomes. In the other groups, a biophysical score of 8 out of 8 within 30 minutes was obtained in 97% (73/75) and 100% (72/72) in groups II and III, respectively; the mean±standard deviation times were 17.1±8.4 minutes (group II) and 13.1±7.3 minutes (group III). No adverse outcomes developed during the study participation in groups I to III.

CONCLUSION

Biophysical scores of 8 out of 8 can be successfully achieved in low-risk periviable pregnancies (20 weeks 0 days to 23 weeks 6 days) within an observation time longer than the standard 30-minute duration. The time required to reach a score of 8 out of 8 decreases as gestation progresses. We suggest adjusting the observation time for biophysical profile completion according to the gestational age.

The uses and limitations of the fetal biophysical profile

In the second half of the twentieth century, true antepartum fetal assessment became possible, mainly due to the advent of real-time ultrasound. Initially, the most widely used form of antepartum fetal assessment was electronic fetal heart rate monitoring, through the nonstress test or the oxytocin-induced contraction stress test. It was soon realized, however, that these forms of monitoring had significant limitations. The biophysical profile allows a more thorough evaluation of fetal well-being and has the potential to significantly reduce the false-positive rate of the nonstress test/contraction stress test.

The predictive value of a nonstress test taken 24 h before delivery in high-risk pregnancies

OBJECTIVES

A series of 180 cases of high risk pregnancies were studied in order to assess if a nonstress test taken 24 h before delivery is of any prognostic significance.

METHODS

To assess the predictability of the NST (reactive or nonreactive) in terms of fetal outcome, the following variables were taken into consideration: fetal distress during labor, low Apgar score (< 7) and perinatal mortality rate.

RESULTS

A reactive test was found to be a good predictor of the healthy fetus (negative predictive value = 91.2%). Also, specificity of the test was found to be 85.4%.

CONCLUSIONS

The nonreactive test could identify a population at risk but it was not helpful as a 'stand alone' modality in decision making, because of the low sensitivity and positive predictive value rates (40.9% and 28.1%, respectively).

The prediction of fetal compromise and acidosis by biophysical profile scoring in the small for gestational age fetus

In a prospective blind study, 133 fetuses suspected of being small for gestational age (SGA), defined as an estimated fetal weight less than the 10th centile for gestation, were monitored by weekly biophysical profile assessment. Perinatal outcome was assessed by umbilical venous blood pH estimation and compared with the profile score determined within seven days of delivery. The positive and negative predictive values of the full biophysical profile score were not significantly better than combinations of two or three of the individual components in this group of fetuses. The use of amniotic fluid volume, non-stress testing and either fetal movement or breathing offers an acceptable alternative to full biophysical profile assessment in the fetus suspected of being small for gestation.

The importance of the behavioural state in biophysical assessment of the term human fetus

We have examined how the different behavioural states exhibited by 78 healthy fetuses at term influence the result of the non-stress test (NST) and biophysical profile score (BPS). In association with state 1F the average recording time to obtain a satisfactory NST and BPS was 27.0 and 26.3 min respectively, and 52.6% and 44.0% respectively failed to achieve a 'normal' result. In contrast, satisfactory results were always obtained in the two active states (2F and 4F), and the average time was 3-5 min. Mature fetuses spend on average one third of the time in state 1F, and knowledge of its characteristics is therefore important, for the interpretation of biophysical tests. Our results suggest that continuation of biophysical recording for at least 40 min is necessary before an unreactive NST or low BPS should be regarded as suspicious. We suggest that interpretation of the NST and BPS should be made in the light of knowledge of normal patterns of behavioural development rather than using an arbitrarily defined scoring system.

Two-tier approach to biophysical assessment of the fetus

The biophysical profile score is widely accepted as a superior predictor of acute-on-chronic fetal asphyxia over the nonstress test. Nevertheless, in the United Kingdom facilities for assessment of high-risk pregnancies by nonstress test are more widely available than with the biophysical profile score. After a retrospective review of 2038 biophysical assessments in 500 high-risk pregnancies, it is suggested that biophysical evaluation of the fetus can be rationalized on the basis of the clinical problem and fetal growth. Terminal acute-on-chronic fetal asphyxia can be excluded by a two-tier method of fetal assessment by initial nonstress test backed up by the biophysical profile score when the nonstress test is suboptimal.

A modified scheme for biophysical profile scoring

A modified scheme for biophysical profile scoring based exclusively on real-time ultrasonographic examination is proposed and includes expanded scores of fetal movements and fetal breathing and only qualitative assessment of accelerated placental maturation, subjective ultrasonographic impression of oligohydramnios, and decreased fetal tone. This method was compared with the method of Vintzileos et al. in the first phase of this observational study and was found to have good correlation in different score categories. This method was then applied in the second phase of the study to 180 high-risk pregnancies to examine correlation with perinatal outcome variables. The relationship between results of the last total score and perinatal outcome variables shows good predictive values. Results of this preliminary study suggest that real-time ultrasonographic evaluation-based scoring of acute fetal events, namely, movements and breathing alone, may have an important role in perinatal management.

Gestational age and fetal biophysical assessment

With improved neonatal care, biophysical assessment to detect fetal asphyxia is used increasingly at an earlier gestational age. We have tested five fetal biophysical variables: nonstress test, fetal breathing movements, fetal movements, fetal tone, and amniotic fluid volume 11,012 times in 5582 singleton fetuses in whom there was a normal perinatal outcome. The nonstress test and fetal breathing movements were more likely to be abnormal at 26 to 33 weeks' gestation compared with 34 to 41 weeks. The nonstress test, fetal breathing movements, fetal tone, and amniotic fluid volume were more likely to be abnormal at 42 to 44 weeks' gestation compared with 37 to 41 weeks. Fetal biophysical tests should be interpreted in relation to gestational age.

Antepartum fetal risk assessment: the role of the fetal biophysical profile score

In the art of medicine we have always known that establishing an accurate diagnosis of health or disease is essential. An active search for the physical signs, both the time honoured and newly discovered, are a crucial step in achieving diagnostic accuracy, in monitoring disease progression, and in assigning prognosis. In extrauterine medicine it is common practice to gather together sets of biophysical data in order to determine immediate health, to monitor condition, and to estimate prognosis: witness the use of vital signs, and, in the newborn, the Apgar score. The providers of perinatal care have known since biblical days that fetal biophysical activities were a reflection of fetal condition (Luke: Chapter 1, Verses 44-45), yet lacked the ability to categorize these activities in an objective and complete manner. The introduction of dynamic ultrasound imaging methods to perinatal medicine at last create the window through which the principles of extrauterine medicine may now be applied to the intrauterine patient--the fetus. Fetal biophysical profile scoring is a method that utilizes this new wealth of information to differentiate the normal fetus from the fetus at risk for death or damage in utero. The method is based on the concept that the discrimination of fetal health and disease improves as more variables are considered. The now extensive clinical experience with the method, in which both overall (gross) and selected (corrected) perinatal death are reduced, while maintaining a remarkably low false negative predictive error, indicate the validity of the concept. Comparative studies lead us to believe that reliance upon single biophysical variables, such as fetal movement counts, or antepartum fetal heart rate monitoring, is no longer of sufficient accuracy to support its use as a sole measure of fetal condition. Looking forward, we anticipate that while the concept on which fetal biophysical profile scoring is based will remain unchanged, inclusion of additional variables is likely to occur. It seems likely that addition of new variables, as may be now measured using high-resolution dynamic ultrasound methods, both B-mode and Doppler, will improve diagnostic accuracy even more. We believe that the application of the current and future modified methods of composite fetal risk assessment will render the occurrence of the tragedy of perinatal loss even more infrequent. While the goal of complete elimination of perinatal deaths remain elusive, this method may be one step towards this goal.

Fetal biophysical profile scoring: selective use of the nonstress test

The fetal biophysical profile score was modified by selective use of the nonstress test. In 2712 study patients (7851 tests) the incidence of nonstress test was reduced to 2.7% with no measurable effect or test accuracy. The nonstress test was most useful in evaluation of abnormal ultrasound monitored variables.

Fetal assessment by biophysical profile scoring: 1985 update

In extrauterine medicine, physicians have come to rely upon sampling of multiple biophysical variables as a means of differentiating states of well-being and compromise. This basic tenet of medicine is expressed by obtaining an Apgar score or some variant in the newborn and as a measure of vital signs in later life. Few, if any, decisions regarding well-being are ever based on a single-variable assessment and, conversely, definition of compromise is rarely based upon a single variable. Through the use of dynamic ultrasound imaging it now becomes possible to visualize the fetus and its biophysical responses in health and disease. Through such visualization it becomes possible to bring to bear some of the basic principles that sustain extrauterine medicine on the intrauterine patient, the fetus. Fetal biophysical profile scoring describes a method that encompasses this concept. The results obtained by application of this method are promising. We would argue that consideration of multiple fetal biophysical variables will, in most instances, yield superior results to single-variable monitoring alone. Hence we have abandoned antepartum fetal heart rate testing as the sole method of fetal risk assessment and used the tool only in conjunction with others of the many variables that may be monitored by dynamic ultrasound methods. This concept of multiple-variable analysis as the superior method for fetal assessment seems clear and well-justified. It is our opinion, however, that the concept of fetal bioprofile scoring may be more important than the method itself in its original description.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer-assisted assessment of the fetal biophysical profile

The biophysical profile assesses fetal heart rate, breathing movements, fetal body movements, amniotic fluid volume, and fetal tone. In the past, these data have been scored by an arbitrary, unweighted system. While this approach is useful in detecting major anomalies and oligohydramnios, both static observations, the dynamic variables (fetal heart rate, fetal breathing movements, and fetal body movements) have added little information beyond that of an extended nonstress test alone. We have evaluated an alternative biophysical assessment system, modeled after extended physiologic studies, which not only acquires dynamic fetal variables simultaneously but, with computer assistance, quantifies the biophysical information. With an ADR 4000/L scanner, a Hewlett-Packard 8040 A monitor, and a specially programmed IBM microcomputer, we studied 100 normal term fetuses during 60-minute epochs. Each gestation had normal amniotic fluid volume and fetal tone. Normative values for the dynamic variables, expressed as means +/- SD were: fetal heart rate, 137 +/- 6.3 bpm; incidence of fetal breathing movements, 25.0% +/- 17.3%; rate of fetal breathing movements, 46.0 +/- 9.4 breaths/min; total fetal breathing movements, 823 +/- 61; incidence of fetal body movements, 8.5% +/- 3.9%; accelerations (greater than 15 bpm, 15 seconds), 14.1 +/- 6.3. We conclude that this approach is practicable, respects the biologic cycles of fetal behavior, and provides a basis for population standards and sequential study of the same fetus.

The nonstress test as a diagnostic test: a critical reappraisal

In the past decade the nonstress test has become a major method of assessing high-risk pregnancy. Although many studies have been published, there has been a lack of rigorous adherence to the standard criteria for diagnostic testing, that is, presentation of test specificity, sensitivity, predictive value, and the prevalence of abnormal outcomes in the populations studied. Furthermore, the populations studied vary widely in composition, testing conditions, methods of test interpretation, and clinical management. The authors undertake a review of these studies, with a focus on these issues, in an attempt to indicate potential problems involved in current test usage and to suggest avenues for needed clinical investigation.

Fetal assessment based on fetal biophysical profile scoring: experience in 12,620 referred high-risk pregnancies. I. Perinatal mortality by frequency and etiology

Fetal biophysical profile scoring was used as a method for antepartum fetal risk assessment in 12,620 high-risk patients referred in a 55-month interval. A total of 26,257 tests were performed on these patients (range, one to 18 tests per patient). Ninety-three perinatal deaths occurred (gross perinatal mortality rate, 7.37 per 1000) of which 62 (66.6%) were due to a major anomaly, seven were due to Rh disease (7.5%), and the remaining 24 deaths (25.8%) occurred in structurally normal fetuses. The corrected perinatal mortality rate was 1.90 per 1000. Eight structurally normal fetuses died within 1 week of a normal test result (corrected false negative rate, 0.634 per 1000). These data suggest fetal biophysical profile scoring is an accurate method for identification of the fetus at risk for perinatal death.

Longitudinal measurements of fetal breathing, body movements, heart rate, and heart rate accelerations and decelerations at 24 to 32 weeks of gestation

Fetal breathing, fetal body movements, fetal heart rate, and fetal heart rate accelerations and decelerations were studied longitudinally in healthy fetuses between 24 and 32 weeks' gestation in the second and third hour following an 800 kcal maternal meal. The expected increase in fetal breathing following a maternal meal was not seen until fetuses were at 30 to 32 weeks' gestation. The number of body movements decreased and the interaction between body movements and fetal heart rate accelerations became more evident as fetuses became older. Fetal heart rate decelerations increased with gestational age, and the relative proportion of total decelerations that were either associated with body movements or were part of a deceleration/acceleration/deceleration complex increased from 24 to 32 weeks' gestation. The data support the hypothesis that gestational age is an important variable to consider when interpreting biophysical measurements in the human fetus at 24 to 32 weeks' gestation. Fetal body movements may be the single most important measurement of fetal health at these gestational ages.