Fifteen years of experience with antepartum fetal testing

Screening for fetal well-being in a high-risk pregnant population comparing the nonstress test with umbilical artery Doppler velocimetry: a randomized controlled clinical trial

OBJECTIVE

The purpose of this study was to evaluate the ability of two different modes of antepartum fetal testing to screen for the presence of peripartum morbidity, as measured by the cesarean delivery rate for fetal distress in labor.

STUDY DESIGN

Over a 36-month period, all patients who were referred to the Fetal Assessment Unit at BC Women's Hospital because of a perceived increased fetal antepartum risk at a gestational age of > or =32 weeks of gestation were approached to participate in this study. Fetal surveillance of these women was allocated randomly to either umbilical artery Doppler ultrasound testing or nonstress testing as a screening test for fetal well-being. If either the umbilical artery Doppler testing or the nonstress testing was normal, patients were screened subsequently with the same technique, according to study protocol. When the Doppler study showed a systolic/diastolic ratio of >90th percentile or the nonstress testing was equivocal (ie, variable decelerations), an amniotic fluid index was performed, as an additional screening test. When the amniotic fluid index was abnormal (<5th percentile), induction and delivery were recommended. When the Doppler study showed absent or reversed diastolic blood flow or when the nonstress test result was abnormal, induction and delivery were recommended to the attending physician. Statistical comparisons between groups were performed with an unpaired t test for normally distributed continuous variables and chi(2) test for categoric variables.

RESULTS

One thousand three hundred sixty patients were assigned randomly to groups in the study; 16 patients were lost to follow up. Six hundred forty-nine patients received Doppler testing and 691 received nonstress testing. The mean number of visits for the Doppler test and nonstress test groups was two versus two, respectively. The major indications for fetal assessment included postdates (43%), decreased fetal movement (22%), diabetes mellitus (11%), hypertension (10%), and intrauterine growth restriction (7%). The incidence of cesarean delivery for fetal distress was significantly lower in the Doppler group compared with the nonstress testing group (30 [4.6%] vs 60 [8.7%], respectively; P <.006). The greatest impact on the reduction in cesarean deliveries for fetal distress was seen in the subgroups in which the indication for testing was hypertension and suspected intrauterine growth restriction.

CONCLUSION

Umbilical artery Doppler as a screening test for fetal well-being in a high-risk population was associated with a decreased incidence of cesarean delivery for fetal distress compared to the nonstress testing, with no increase in neonatal morbidity.

The efficacy of the non-stress test in preventing fetal death in post-term pregnancy

We conducted a case--control study to examine the efficacy of non-stress testing in preventing fetal death in post-term pregnancy. The analysis was based on data from the 1988 National Maternal and Infant Health Survey, which was a nationally representative sample of live births, fetal deaths and infant deaths that occurred in 1988. Information on whether a woman had non-stress testing was obtained from a questionnaire sent to prenatal care providers and hospitals. Cases were post-term women (with 42 weeks or more gestation) who had fetal deaths. Three post-term controls, who had live births and who delivered at the same time or later than the cases, were randomly chosen and individually matched to each case by maternal race. The proportion of women who had one or more non-stress tests during pregnancy was compared between cases and controls. Non-stress testing was used in 30.9% of the 126 cases and in 28.5% of the 375 controls. The race-adjusted odds ratio for exposure to non-stress test was 1.12 [95% CI 0.72, 1.75]. After controlling for other important confounding variables the odds ratio was 1.05 [95% CI 0.57, 1.91]. These results do not support the efficacy of non-stress testing in post-term pregnancies. A more detailed evaluation of this widely used screening procedure is needed.

Nonstress testing and contraction stress testing

Antepartum fetal heart rate (FHR) testing, including the nonstress test and contraction stress test, has evolved in clinical usage over the past 3 decades. Although the nonstress test has become a standard of care in high-risk pregnancy, it has been modified by the use of fetal stimulation (vibroacoustic stimulation) and the addition of automated fetal movement recording (actocardiotocography). In all of its formats, antepartum FHR testing has been associated with reduction of preventable fetal loss. More recently, there have been attempts to improve test efficacy by computer-enhanced approaches.

Applying statistical, uncertainty-based and connectionist approaches to the prediction of fetal outcome: a comparative study

A common situation in the field of medicine is the availability of a huge quantity of data and knowledge relevant to a problem which is nevertheless, to a greater or lesser degree, incomplete or imprecise. This kind of problem occurs, for example, with respect to the information available for the prognostic tasks required for pregnancy monitoring, where decision-making by physicians calls for the incorporation of predictive skills. There are available however, several knowledge discovery methods that can be applied to data resulting from the performance of one or several of the non-stress tests (NSTs) that are used to evaluate a pregnant patient's antenatal status. This paper presents, discusses and compares the results obtained as a consequence of the application of different prediction methods, namely the Bayes' model, discriminant analysis, artificial neural networks (ANNs) and the Shortliffe and Buchanan uncertainty-based model.

Determinants of the optimal time in gestation to initiate antenatal fetal testing: a decision-analytic approach

To identify the most important determinants of the optimal timing for the initiation of antenatal fetal testing in a high-risk pregnancy (such as insulin-dependent diabetes mellitus), we performed a decision analysis based on a Markov model. The model incorporated several components: test sensitivity and specificity and week-specific probability estimates for fetal death, delivery, and neonatal morbidity and mortality. The analysis demonstrated that the optimal time in gestation to begin testing (from the combined standpoint of both maximizing neonatal survival and minimizing fetal death) was highly dependent on test specificity, the cumulative risk of fetal death (and its distribution throughout gestation), and the week-specific probabilities of neonatal death. For example, even with the increased risk of fetal death associated with insulin-dependent diabetes, very high test specificity (> 99%) is required to recommend testing before 30 weeks. If tests of lower specificity (higher false-positive rates) are used, neonatal deaths will increase and will not be offset by a corresponding decrease in fetal deaths. By performing sensitivity analyses, we demonstrated the effect and relative importance of the model components for determining the optimal gestational age to initiate fetal testing.

Antepartum surveillance in diabetic pregnancies: predictors of fetal distress in labor

OBJECTIVE

Our purpose was to evaluate an antepartum testing program based on twice-weekly nonstress testing and amniotic fluid evaluation in pregnancies complicated by diabetes mellitus and to weight the test components in the prediction of fetal distress requiring cesarean delivery.

STUDY DESIGN

During the 4-year period of 1987 through 1990, 2134 women with pregnancies complicated by diabetes underwent antepartum testing. Of these 1501 women (class A1, n = 505; A2-diet, n = 305; A2-insulin, n = 580; B, n = 71; C to D, n = 29; R to F, n = 11) were delivered within 4 days of their last test. Categoric analysis of data was performed according to diabetic class, fetal heart rate results, and the presence of decreased, normal, or increased amniotic fluid assessment. A univariate logistical regression was first conducted with cesarean delivery for fetal distress as outcome variable by use of the following variables: fetal weight and sex, diabetic class, gestational age at delivery, presence of additional indications for antepartum testing, largest vertical pocket, amniotic fluid index (summation of the four quadrants of the largest vertical pocket), nonstress test reactivity (two accelerations of > or = 15 beats/min of 15 seconds' duration), presence of decelerations (> or = 15 beats/min for 15 seconds) during the nonstress test, and the interactions of the nonstress test with deceleration, largest vertical pocket, and amniotic fluid index. Multivariate analysis was then applied to predict the best model.

RESULTS

No stillbirths occurred within 4 days of the last antepartum test. However, the corrected stillbirth rate of the entire tested population was 1.4 per 1000. Eighty-five women required cesarean delivery for fetal distress. The factors most predictive of cesarean delivery for fetal distress (p < 0.05, odds ratio and 95% confidence interval) were a deceleration (3.60, 2.14 to 6.06), nonreactive nonstress test (2.68, 1.60 to 4.49), and the interaction of both a nonreactive nonstress test and decelerations (5.63, 2.67 to 11.9). Amniotic fluid assessment by largest vertical pocket or amniotic fluid index were not statistically significant. The multivariate analysis selected the interaction of nonstress test and deceleration as the best significant predictor for cesarean delivery for fetal distress.

CONCLUSION

An antepartum fetal surveillance program using twice-weekly nonstress test and fluid index assessment in pregnancies complicated by diabetes was successful in preventing stillbirth. The absence of fetal heart rate reactivity and the presence of decelerations were predictive of the diagnosis of fetal distress in labor requiring cesarean delivery. Ultrasonographic assessment of amniotic fluid volume was not a significant predictor of fetal distress in labor in the diabetic pregnancy.

Neural network prediction of nonstress test results: how often should we perform nonstress tests?

OBJECTIVE

Our purpose was to predict outcomes and optimal intervals for nonstress tests of term gravid women with neural networks.

STUDY DESIGN

We studied 100 normal term patients whose 30-minute nonstress tests, performed on 5 consecutive days, were computer analyzed for the following elements: fetal heart rate baseline, variability, signal loss, accelerations (> 15 beats/min), and decelerations. The training set used 65 patients; the testing, 35 patients. Nonstress test data (days 1 to 4) were inputs; day 5 data were training patterns. Networks for each nonstress test element used Brainmaker Macintosh 1.0 (California Scientific Software, Nevada City, Calif.) trained to 0.12 tolerance. Actual fetal heart rate elements and their daily differences were compared with predictions by the networks and multiple regressions.

RESULTS

There was little difference between networks using daily or alternate-day inputs for predicting test performance on day 5; networks using test intervals > 2 days could not be trained to tolerance. Long-term fetal heart rate variation was the nonstress test element best predicted. Daily differences networks provided better prediction of all day 5 data than did actual daily values networks or multiple regression formulas.

CONCLUSIONS

Baseline long-term fetal heart rate variability seems to be the most predictable fetal heart rate element over time and should merit more consideration in overall fetal testing. Fetal heart rate elements are not easily predicted by any method for intervals longer than 2 days. Using longer test intervals might run a greater risk for unanticipated changes in nonstress test outcomes, even when fetal condition is normal.

The NST-EXPERT project: the need to evolve

NST-EXPERT is a medical expert system designed to evaluate fetal condition (especially in 'high risk' pregnancies). The system reasons based on data from the Non-Stress Test (NST), a monitoring test widely used in obstetrics. From specific limited maternal-fetal context information together with the analysis of the NST results the system infers a diagnosis for each case, elaborates a therapeutic plan, and suggests a prognosis of an early neonatal outcome. This article describes a new version based on a previous research prototype. Such systems can aid clinicians of varied experience in assessing and managing complicated pregnancies.

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).