Obstetric ultrasound and biophysical scoring

One of the major challenges that obstetricians encounter during the management of high risk pregnancy is prematurity of the foetus with its associated complications. Various surveillance tests have been developed to evaluate the well-being of the foetus during a specified interval of time. Some of these include the oxytocin challenge test/contraction stress test, (CST), nonstress test (NST; Cardiotocograph CTG in the UK), biophysical profile (BPP) and doppler evaluation of foetal blood flow.
Though each of these tests are useful in providing certain aspects of foetal wellbeing none of these tests independently have sufficient sensitivity or specificity to provide the absolute proof of foetal health.
In 1980 Manning1 and his colleagues proposed the foetal BPP as a method to assess foetal well-being and to identify compromised foetus. Their publication suggested that combined foetal biophysical testing was a more accurate method of antepartum foetal evaluation than any single method.
This review article aims to provide an overview of BPP in the evaluation of high risk foetuses.

Description

The BPP scores five foetal variables: foetal heart rate, foetal breathing, foetal movement, foetal tone, and amniotic fluid volume. Foetal heart rate, breathing, movement and tone are acute markers of foetal status while amniotic fluid volume is a chronic marker.
An ultrasound is used to measure foetal breathing, foetal movement, foetal tone, and amniotic fluid volume. The foetal heart rate is assessed using a CTG.
Each parameter is given a score of two or zero, based on specific criteria. The total potential score is a 10. The scoring criteria for these variables are depicted in Table 1.

 

 

Procedure

The mother is positioned on a comfortable couch and the ultrasonographic parameters of the BPP are scored while noting the starting time.The profile may be completed when all of the variables have been observed; however, a full 30 minutes must elapse before the profile is judged to be abnormal. The scan should start with a general survey, looking at the position of the foetus and the presence of cardiac activity.
Foetal breathing (FB) is measured by watching for movement of the foetal thorax and diaphragm. This is to assure breathing, and not just chest wall movement.
Foetal movement is defined by gross arm, leg, or body activity. Facial movement is not scored.
Foetal tone is defined by active extension and flexion of the foetal limbs, trunk, or hand; or if the hand remains in a flexed position during the entire 30-minute test.
Amniotic fluid volume is estimated by measuring pockets of fluid on ultrasound. In this method, the largest vertical column of fluid in each of the four uterine quadrants is measured. Amniotic fluid volume is an important variable in foetal wellbeing assessment because of the role of the foetus in its production and control. A reduction in the fluid volume indicates chronic foetal compromise.
Foetal heart rate is measured using the CTG. The foetal heart rate is normally variable in nature. Accelerations, or increases in FHR, are usually seen in response to foetal movements and are therefore reassuring.

Indications

Populations where antepartum foetal assessment has been shown to reduce neonatal morbidity and/or mortality include: small for gestational age foetus, pre-eclampsia/chronic hypertension, postdates pregnancy (>294 days), preterm premature rupture of membranes, decreased foetal movement, pre-pregnancy diabetes, insulin requiring gestational diabetes. BPP can be a very useful tool under these circumstances however it should be borne in mind that some components of the test itself might not be reliable in accurate interpretation of the results. For example polyhydramnios which may be associated with diabetes and oligohydramnios due to ruptured membranes will give a false score for the amniotic fluid component of the test.
A BPP normally is not performed before the second half of a pregnancy, since foetal breathing movements do not occur in the first half. The BPP may be considered following a non-reactive NST; after a suspicious oxytocin challenge/contraction stress test; or after term, especially if there is concern about low amniotic fluid volume.

Physiological basis of the test

Each of the components evaluated in the BPP results from efferent signals originating in different central nervous system (CNS) centres, which mature at different gestational ages as shown in Table 2.

 

 

Factors affecting BPP

Foetal sleep, gestations less than 33 weeks or more than 42 weeks, maternal glucose, alcohol ingestion, maternal magnesium administration, rupture of membranes and labour are some of the factors affecting the biophysical profile scoring. Foetal breathing movements are reduced during maternal fasting.2

Clinical implications

The presence of biophysical variables with a score of two for each component implies absence of significant central nervous system hypoxemia/acidemia at the time of testing. By comparison, a compromised foetus typically exhibits loss of accelerations of the foetal heart rate (FHR), decreased body movement and breathing, hypotonia, and, less acutely, decreased amniotic fluid volume.
In unstable pregnancies with progressive deterioration of the foetal condition, abnormal umbilical cord blood flow patterns occur first. Subsequently, FHR variation is reduced, followed by loss of breathing movements, while general foetal movements and tone are the last parameters to demonstrate abnormal results. Frequent assessment of foetal BPP movements may help prolong the pregnancy in foetuses with a marginally reduced FHR variation.
A non-reassuring test may be repeated four to 24 hours later for comparison. Efforts should be made to assess for false negatives or false positives. A low BPP score may be followed by interventions with their own potential complications.

Interpretation

Manning’s studies indicated that a score of eight or ten out of ten provides a reassuring BPP score. If the score is eight, with a decrease in amniotic fluid volume, delivery may be indicated, with foetal maturity. A score of six arouses suspicions of chronic foetal hypoxia. A repeat test within four to six hours may be performed. Delivery may be indicated if there is a reduction in the amniotic fluid volume. A score of four is suspicious of chronic foetal hypoxia. Delivery is indicated if a repeat BPP after 24 hours confirms a score of four or below. A score of zero to two elicits a strong suspicion of chronic foetal hypoxia. The BPP testing period may continue for two hours instead of the usual 30 minutes. If the two-hour score is four or below, delivery is indicated if the foetus has a good chance at extrauterine survival.

Modifications

Since the introduction of the BPP several modifications have been suggested to decrease the time needed to perform the test and improve the validity of the test. The widely used modifications are summarised below.
Vintzileos’ modification of the BPP includes all the criteria used in the classical BPP scoring as well as the placental grading. The maximum possible score by this method is 12, any score below seven implying a compromised foetus.3 A higher placental grade suggests a chronic condition compromising foetal wellbeing.
A modified biophysical profile consisting of a nonstress test and an amniotic fluid index (AFI), is used widely.4 If either the NST or the AFI is abnormal, a complete BPP or a contraction stress test is performed. Nageotte et al in their study found that the modified biophysical profile was a reliable means of foetal surveillance and identified at increased risk for adverse perinatal outcome and small-for-gestational-age infants.5 Further they stated that the modified BPP, CST, and complete BPP have similar low false-negative mortality rates, defined as the number of foetal deaths within one week of a normal test result.
Nevertheless, Miller et al showed that no clear evidence exists that the two variables used in the modified BPP are better predictors than the other variables omitted from the BPP.6 Furthermore, this method requires two modalities for foetal evaluation, while normal ultrasonographic findings in a BPP eliminate the need for an NST.
Foetal acoustic stimulation used in several centres. This method aims to decrease the BPP testing time and to reduce the number of non-reassuring tests, by delivering three seconds of acoustic stimulation if foetal breathing, tone, or movement were not present during the first five minutes of the study.7

Application

Antepartum testing using the BPP should not be performed earlier than the period of viability. This test is performed to gain time in patients in whom induction of labour may be unsuccessful due to an unfavourable cervix. In these patients, the purpose of the BPP is to avoid the maternal morbidity resulting from failed induction followed by caesarean delivery.
The frequency of testing depends on the clinical indications and the severity of the maternal or foetal condition. In most high-risk pregnancies, weekly testing would be recommended, however  in post term pregnancies beyond 42 weeks for patients with insulin-dependent diabetes twice-weekly testing should be considered.
In most cases, testing is not instituted until there is demonstrable clinical evidence of maternal (eg, preeclampsia) or foetal (eg, IUGR) disease. The exception is the diabetic pregnancy where testing is begun at 28 weeks in class one diabetics and at 32 weeks in gestational diabetics, even if there is no other evidence of pregnancy complications.8
If an abnormal score occurs in a term foetus, preparation should be made for delivery. An abnormal score in a foetus remote from term requires conservative management, since the risk of foetal death is similar to the neonatal mortality rate resulting from prematurity. In these patients, daily testing often is performed. Table 3 provides general guidelines for management following the BPP testing.

 

 

Reliability of the test

A Cochrane systematic review conducted on the use of BPP in foetal assessment in high risk pregnancies concluded that there was no difference found between biophysical profile and other forms of foetal assessment over a range of foetal and neonatal measures.9,10 These authors included five trials, involving 2,974 women. They stated that most trials were of poor quality and found no significant differences between the groups in perinatal deaths or Apgar score less than seven at five minutes. There was an increased risk of caesarean section in the BPP group. They suggested additional studies to be definitive regarding the efficacy of BPP in high-risk pregnancies.
In contrast other studies have stated that BPP has a false-negative mortality rate of 0.77 deaths per 1,000 tests.11 BPP has shown to have a high correlation with the antepartum foetal umbilical venous cord pH level. Cordocentesis performed immediately following a BPP demonstrated that a pH of less than 7.20 was associated with a poor BPP score whilst a score of ten of ten always yielded a pH of greater than 7.20.12 Vintzileos et al’s study suggested that the biophysical profile was very accurate in the identification of the foetus with academia.13
This fact is further supported by a large study wherein a normal foetal biophysical profile score confers a high probability of perinatal survival.14 A foetus with a low score especially in the last BPP score has been shown to have a high perinatal mortality rate, higher incidence of foetal distress, admission to the neonatal unit, intrauterine growth restriction, five minute Apgar score less than seven and umblical artery pH less than 7.20. These data strongly suggest the biophysical profile scoring method of foetal risk assessment is accurate and also provides insight into the extent of foetal compromise.15
Manning et al compare the BPP with NST and suggested that foetal biophysical profile scoring had a higher sensitivity, specificity and accuracy nevertheless did not show any significant differences when compared with the nonstress test. The negative predictive value between the two methods was similar.16
There was a demonstrable reduction in the incidence of cerebral palsy when BPP was used as a tool in antepartum assessment when compared with untested patients. A low score increases the likelihood of cerebral palsy.17

 

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Advantages

The test is non-invasive in nature and generally well tolerated.
It has a low false negative rate.
It assesses the acute and chronic markers of foetal hypoxia and helps detect various degrees of foetal compromise.

Disadvantages

The complete BPP is a time-consuming and a more expensive test when compared to NST. Foetal parameters are recorded over a 30-minute time period, with an additional 30 minutes for the CTG component. It requires a trained professional to perform the test. The NST records the relationship of foetal heart rate to foetal movement. It is associated, however, with a false-positive rate as high as 80%, and averaging about 50%.
An abnormal score may indicate a normal rest activity cycle and as mentioned previously the amniotic fluid volume cannot be accurately scored in polyhydramnios and oligohydramnios.

Conclusion

The biophysical profile testing gives a numerical score and thus an objective assessment of the various physiological components of the foetus that can be compromised due to foetal hypoxia and academia. Such a scoring system will provide the clinician with criteria that will enable uniformity in the management of high risk foetuses. When the BPP identifies a compromised foetus, measures can be taken to intervene before progressive metabolic acidosis leads to foetal death.
However there is insufficient evidence from randomised trials to support the use of BPP as a test of foetal wellbeing in high-risk pregnancies and further robust studies are imperative to establish the applicability of this test.
In the United Kingdom, BPP is not commonly undertaken by most Foetal Medicine Consultants. Aspects of the test are however casually performed in what could be termed ‘modified BPP’ testing. To some extent, it is deemed somewhat subjective despite its widespread utilisation in the United States.

References

  1. Manning FA, Platt LD, Sipos L. Antepartum fetal evaluation: development of a fetal biophysical profile. Am. J. Obstet. Gynecol. 1980 Mar 15;136(6):787–95.
  2. Mirghani HM, Weerasinghe DSL, Ezimokhai M, Smith JR. The effect of maternal fasting on the fetal biophysical profile. Int J Gynaecol Obstet. 2003 Apr;81(1):17–21.
  3. Vintzileos AM, Campbell WA, Ingardia CJ et al. The fetal biophysical profile and its predictive value.Obstet Gynecol. 1983; Sept 62:271-8.
  4. Eden RD, Seifert LS, Kodack LD et al. A modified biophysical profile for antenatal fetal surveillance. Obstet Gynecol. 1988; Mar 71:365-9.
  5. Nageotte MP, Towers CV, Asrat T, Freeman RK. Perinatal outcome with the modified biophysical profile. Am. J. Obstet. Gynecol. 1994 Jun;170(6):1672–6.
  6. Miller DA, Rabello YA, Paul RH. The modified biophysical profile: antepartum testing in the 1990s. Am. J. Obstet. Gynecol. 1996 Mar;174(3):812–7.
  7. Pinette MG, Blackstone J, Wax JR, Cartin A. Using fetal acoustic stimulation to shorten the biophysical profile. Journal of Clinical Ultrasound. 2005;33(5):223–5.
  8. Graves CR. Antepartum fetal surveillance and timing of delivery in the pregnancy complicated by diabetes mellitus. Clin Obstet Gynecol. 2007 Dec;50(4):1007–13.
  9. Alfirevic Z, Neilson JP. Biophysical profile for fetal assessment in high risk pregnancies. Cochrane Database Syst Rev. 2000;(2):CD000038.
  10. Lalor JG, Fawole B, Alfirevic Z, Devane D. Biophysical profile for fetal assessment in high risk pregnancies. Cochrane Database Syst Rev. 2008;(1):CD000038.
  11. Dayal AK, Manning FA, Berck DJ, Mussalli GM, Avila C, Harman CR, et al. Fetal death after normal biophysical profile score: An eighteen-year experience. Am. J. Obstet. Gynecol. 1999 Nov;181(5 Pt 1):1231–6.
  12. Vintzileos AM, Gaffney SER, Salinger LMR, Campbell WA, Nochimson DJ. The Relationship Between Fetal Biophysical Profile and Cord pH in Patients Undergoing Cesarean Section Before the Onset of Labor. Obstetrics & Gynecology August 1987. 1987;70(2):196–201.
  13. Vintzileos AM, Campbell WA, Rodis JF, McLean DA, Fleming AD, Scorza WE. The relationship between fetal biophysical assessment, umbilical artery velocimetry, and fetal acidosis. Obstet Gynecol. 1991 Apr;77(4):622–6.
  14. Manning FA, Morrison I, Harman CR, Lange IR, Menticoglou S. Fetal assessment based on fetal biophysical profile scoring: experience in 19,221 referred high-risk pregnancies. II. An analysis of false-negative fetal deaths. Am. J. Obstet. Gynecol. 1987 Oct;157(4 Pt 1):880–4.
  15. Manning FA, Harman CR, Morrison I, Menticoglou SM, Lange IR, Johnson JM. Fetal assessment based on fetal biophysical profile scoring. IV. An analysis of perinatal morbidity and mortality. Am. J. Obstet. Gynecol. 1990 Mar;162(3):703–9.
  16. Manning FA, Lange IR, Morrison I, Harman CR. Fetal biophysical profile score and the nonstress test: a comparative trial. Obstet Gynecol. 1984 Sep;64(3):326–31.
  17. Manning FA, Bondaji N, Harman CR, Casiro O, Menticoglou S, Morrison I, et al. Fetal assessment based on fetal biophysical profile scoring: VIII. The incidence of cerebral palsy in tested and untested perinates. American Journal of Obstetrics & Gynecology. 1998 Apr;178(4):696–706.
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