A prospective analysis of the influence of gestational age on the baseline fetal heart rate and reactivity in a low-risk population

Characteristics of Heart Rate Tracings in Preterm Fetus

Background and Objectives: Prematurity is currently a serious public health issue worldwide, because of its high associated morbidity and mortality. Optimizing the management of these pregnancies is of high priority to improve perinatal outcomes. One tool frequently used to determine the degree of fetal wellbeing is cardiotocography (CTG). A review of the available literature on fetal heart rate (FHR) monitoring in preterm fetuses shows that studies are scarce, and the evidence thus far is unclear. The lack of reference standards for CTG patterns in preterm fetuses can lead to misinterpretation of the changes observed in electronic fetal monitoring (EFM). The aims of this narrative review were to summarize the most relevant concepts in the field of CTG interpretation in preterm fetuses, and to provide a practical approach that can be useful in clinical practice. Materials and Methods: A MEDLINE search was carried out, and the published articles thus identified were reviewed. Results: Compared to term fetuses, preterm fetuses have a slightly higher baseline FHR. Heart rate is faster in more immature fetuses, and variability is lower and increases in more mature fetuses. Transitory, low-amplitude decelerations are more frequent during the second trimester. Transitory increases in FHR are less frequent and become more frequent and increase in amplitude as gestational age increases. Conclusions: The main characteristics of FHR tracings changes as gestation proceeds, and it is of fundamental importance to be aware of these changes in order to correctly interpret CTG patterns in preterm fetuses.

Longitudinal evaluation of computerized cardiotocographic parameters throughout pregnancy in normal fetuses: a prospective cohort study

INTRODUCTION

The longitudinal cardiotocographic (CTG) changes throughout pregnancy in normal fetuses have never been fully described. We aimed at characterizing the evolution of CTG parameters in healthy fetuses, from 24 to 41 weeks of gestation.

MATERIAL AND METHODS

A prospective cohort study was conducted in singleton fetuses without structural abnormalities on second-trimester ultrasound. At least one CTG was performed in each of the following intervals: 24-26 weeks(+6d) , 27-29 weeks(+6d) , 30-32 weeks(+6d) , 33-35 weeks(+6d) , 36-38 weeks(+6d) and ≥39 weeks; tracings were analyzed by the OMNIVIEW-SISPORTO 3.6 system. Cases of preterm delivery, fetal death, birthweight under the 10th percentile, low five-minute Apgar, umbilical artery acidemia or neonatal intensive care unit admission were subsequently excluded.

RESULTS

A total of 1049 eligible tracings were obtained from 145 fetuses. There was a significant increase over time in average long-term variability (LTV), average short-term variability (STV), number of accelerations and uterine contractions. Conversely, fetal heart rate (FHR) baseline and number of decelerations decreased. A high inter-fetal variability was observed, but there was considerable intra-fetal consistency. Fetuses showing a marked decrease in FHR baseline and those with a marked increase in average LTV had a significantly lower birthweight. Cesarean section rate was significantly higher in cases with a decrease in average STV throughout gestation.

CONCLUSIONS

This prospective longitudinal study shows an evolution in computerized CTG parameters during pregnancy, indicating the need to adapt interpretation criteria based on gestational age. The high inter-fetal variability and considerable intra-fetal consistency suggests the possible value of using each fetus as its own reference in serial assessments.

Nonstress testing at ≤ 32.0 weeks' gestation: a randomized trial comparing different assessment criteria

OBJECTIVE

Comparison of time and outcomes of National Institutes of Child Health and Human Development defined fetal heart rate acceleration criteria at ≤ 32 weeks (≥ 10 beats/min, ≥ 10 seconds) compared with standard criteria (≥ 15 beats/min, ≥ 15 seconds).

STUDY DESIGN

Singleton high-risk pregnancies that were referred for nonstress testing at ≤ 32 weeks' gestation were randomly assigned to 15 × 15 or 10 × 10 criteria. Data included nonstress test information, maternal data, and outcomes.

RESULTS

One hundred forty-three women were randomly assigned to 15 × 15 (n = 71) or 10 × 10 (n = 72). The groups were similar in maternal and pregnancy characteristics. Median time to reactive nonstress testing was shorter in the 10 × 10 group (37.3 minutes) than the 15 × 15 group (41.3 minutes; P = .04). There were no serious adverse events.

CONCLUSION

The time to attain a reactive nonstress testing at ≤ 32 weeks' gestation was 4 minutes shorter when the 10 × 10 criteria were used. There were no adverse events related to use of 10 × 10 nonstress testing criteria.

Effect of maternal stress on fetal heart rate assessed by vibroacoustic stimulation

This study was designed to determine whether maternal stress levels, state and trait anxiety levels, and stress hormones affect fetal heart rate (FHR) patterns after vibroacoustic stimulation (VAS) at 30 weeks of gestation. A total of 24 healthy pregnant women with a single fetus pregnancy were enrolled. Corticotropin releasing hormone (CRH) and adrenocorticotropic hormone in maternal plasma and cortisol, and chromogranin A in saliva were measured. The FHR patterns after VAS were divided into three types: type I, a long period of acceleration or one acceleration lasting > 1 min or at least two accelerations lasting > 15 s; type II, a biphasic response with acceleration followed by deceleration; and type III, no response or prolonged deceleration. In the high trait anxiety group, CRH levels were significantly higher than in the low trait anxiety group, and FHR patterns after VAS showed mostly a type II response pattern. These findings suggest that stress in pregnant women with high trait anxiety may influence FHR patterns after VAS.

Maternal position during non-stress test and fetal heart rate patterns

OBJECTIVE

The aim of the study was to determinate whether maternal position during the non-stress test (NST) in different weeks of pregnancy influences fetal heart rate patterns.

MATERIALS AND METHODS

A total of 1055 NST lasting 30 min were performed in 368 autochthonous mothers with low-risk pregnancies. On the basis of maternal position during the test we divided into three groups: reclining, sitting, and walking. The cardiotocographic parameters considered were: number of minutes of reactive NST with minimum length, number of fetal movements, fetal heart rate baseline, number of large accelerations, number of dubious NST, and number of variable decelerations.

RESULTS

Fetal heart rate patterns in low-risk pregnancies were studied using NST in different gestational ages and in different maternal positions. Differences in heart rate were found in relationship to both gestational age and maternal position. The minimum length of NST necessary to record at least three large accelerations was significantly different in relationship to both gestational age and maternal position. The number of fetal movements perceived by the mother was greater in the reclining position than in sitting or walking. Together with the progression of pregnancy, the number of dubious NST decreased in all subgroups, especially in the sitting position. The greatest number of variable decelerations was observed in the reclining position and it was increased with pregnancy progression. The NST duration did not vary greatly in the reclining position, but in the sitting position or during walking, the time taken to record the three large accelerations required to define the trace as reactive, decreased significantly with the progression of pregnancy

CONCLUSIONS

Non-stress test in sitting position or during walking should be encouraged because fetal reactivity is more quickly observed.

Risks and benefits of nicotine to aid smoking cessation in pregnancy

Cigarette smoking during pregnancy is the single largest modifiable risk for pregnancy-related morbidity and mortality in the US. Addiction to nicotine prevents many pregnant women who wish to quit smoking from doing so. The safety and efficacy of nicotine replacement therapy (NRT) for smoking cessation during pregnancy have not been well studied. Nicotine is classified by the US Food and Drug Administration as a Pregnancy Category D drug. Animal studies indicate that nicotine adversely affects the developing fetal CNS, and nicotine effects on the brain may be involved in the pathophysiology of sudden infant death syndrome (SIDS). It has been assumed that the cardiovascular effects of nicotine resulting in reduced blood flow to the placenta (uteroplacental insufficiency) is the predominant mechanism of the reproductive toxicity of cigarette smoking during pregnancy. Short term high doses of nicotine in pregnant animals do adversely affect the maternal and fetal cardiovascular systems. However, studies of the acute effects of NRT in pregnant humans indicate that nicotine alone has minimal effects upon the maternal and fetal cardiovascular systems. Cigarette smoking delivers thousands of chemicals, some of which are well documented reproductive toxins (e.g. carbon monoxide and lead). A myriad of cellular and molecular biological abnormalities have been documented in placentas, fetuses, and newborns of pregnant women who smoke. The cumulative abnormalities produced by the various toxins in cigarette smoke are probably responsible for the numerous adverse reproductive outcomes associated with smoking. It is doubtful that the reproductive toxicity of cigarette smoking is primarily related to nicotine. We recommend the following. Efficacy trials of NRT as adjunctive therapy for smoking cessation during pregnancy should be conducted. The initial dose of nicotine in NRT should be similar to the dose of nicotine that the pregnant woman received from smoking. Intermittent-use formulations of NRT (gum, spray, inhaler) are preferred because the total dose of nicotine delivered to the fetus will be less than with continuous-use formulations (transdermal patch). A national registry for NRT use during pregnancy should be created to prospectively collect obstetrical outcome data from NRT efficacy trials and from individual use. The goal of this registry would be to determine the safety of NRT use during pregnancy, especially with respect to uncommon outcomes such as placental abruption. Finally, our review of the data indicate that minimal amounts of nicotine are excreted into breast milk and that NRT can be safely used by breast-feeding mothers.

Computerized analysis of fetal heart rate parameters by gestational age

OBJECTIVE

The aim of this study is to define the reference ranges for fetal heart rate (FHR) parameters according to gestational age, by determining the relationship between the FHR and gestational age using a computerized FHR analysis system.

METHODS

Using our own software developed by Hanyang University Hospital in Korea, non-stress tests were performed for 20 min. FHR parameters for 6455 subjects were analyzed for various gestational groups; <25 weeks, 25-28 weeks, 29-32 weeks, 33-36 weeks, 37-40 weeks, and >40 weeks.

RESULTS

The FHR parameters were related to gestational age. The mean baseline FHR, signal loss, and fetal movements decreased significantly with gestation (P<0.0001). The variability and accelerations of FHR were highest for the 37-40 weeks gestational group (P<0.05).

CONCLUSIONS

The results showed that overall, the differences in the FHR parameters between gestational groups were statistically significant, and the gestational age of the fetus should be considered when interpreting FHR patterns.

Physical conditioning effects on fetal heart rate responses to graded maternal exercise

PURPOSE

This study examined the effects of advancing gestational age and maternal aerobic conditioning (stationary cycling) on fetal heart rate (FHR) responses to strenuous non-steady-state maternal exercise.

METHODS

Subjects chose to participate in either an exercise group (EG) or control group (CG). Fourteen healthy, previously sedentary pregnant women participated in the exercise group, and six pregnant controls remained sedentary. Stationary cycling (heart rate target: 145 beats x min(-1)) was performed 3 d x wk(-1) by the exercised group. Exercise duration was increased from 14 to 25 min x session(-1) during the second trimester and was maintained at 25 min x session(-1) throughout the third trimester. FHR was monitored before, during, and after a progressive submaximal cycle ergometer test (peak heart rate = 170 beats x min(-1)) performed at approximately 27 and 37 wk gestation.

RESULTS

Mean FHR increased significantly (P < 0.05) during exercise, followed by a modest suppression and then a delayed rise during the recovery period at both observation times. Fetal bradycardia was not observed in any of the exercise tests. Effects of advancing gestational age included a lower FHR baseline both at rest and in response to maternal exercise and a lower incidence of exercise-induced tachycardia. Maternal physical conditioning did not significantly alter FHR response to maternal exercise.

CONCLUSION

Our results support the hypothesis that FHR responses to strenuous exercise are altered by advancing gestational age and a brief progressive exercise test terminated at a maternal heart rate of 170 beats x min(-1) does not induce fetal distress during a healthy pregnancy.

Gestational age related changes in cardiac dynamics of the fetal baboon

To provide insight into the maturation of neural mechanisms governing fetal heart rate and rate variability, seven chronically instrumented fetal baboons were monitored under steady state conditions between 120 and 165 days gestation (term 175 d). Forty records of 24 h duration (5-7 records/fetus) were evaluated. For each fetus, heart rate decreased with gestational age (mean+/-SD, r = -0.530+/-0.324, P <0.05). In contrast, there were increases with age in markers of various components of autonomic control of fetal R-wave to R-wave interval (RRi) variability as reflected in a positive correlation with age for all fetuses of SD RRi (r = 0.656+/-0.347, P < 0.01), root mean squared differences in RRi (r = 0.686+/-0.223, P <0.05), and power at low frequency in the RRi spectrum (r = 0.800+/-0.161 P < 0.01). In each of the seven fetuses, scatter plots of RRi as a function of the prior RRi (Poincare plots) had increased dispersion around the median with gestational age (0.605+/-0.371, P<0.05). Additional measures of variability evaluated changes in RRi from one interval to the next (deltaRRi). The incidence of sustained deltaRRi changes, either decelerations or accelerations, rose with gestation (r = 0.920+/-0.057, P < 0.001) while the incidence of no detected deltaRRi changes (<+/-1 ms) diminished (r = - 0.649+/-0.364, P <0.05). Sequential decreases in fetal heart rate, increases in RRi variability and increases in changes in RRi and deltaRRi with age imply an overall maturation in autonomic cardio-regulatory control processes. Increases with gestation in measures of high frequency components of variability are compatible with enhanced parasympathetic modulation of fetal heart rate.

The incidence of abnormal findings from intrapartum cardiotocogram monitoring in term and preterm labours

A retrospective analysis of 514 consecutive labours delivering 530 babies over a period of 18 months was conducted by a high-risk pregnancy team in a tertiary teaching unit to compare the incidence of abnormal findings from intrapartum monitoring between labours occurring before and at or after 34 weeks' gestation. Those delivered by elective Caesarean section, or Caesarean section at the onset of labour because of contraindications to labour and vaginal delivery, and those with congenitally malformed fetuses were excluded. Tracings were scored using the FIGO 1987 guidelines. Seventy-four labours and 83 babies delivered before 34 weeks, and 440 labours and 447 babies delivered after 34 weeks in the study. There was a slightly higher incidence of suspicious CTG tracings (33.7% versus 19.6%, OR 2.66, 95% CI 1.6-4.4) in the preterm group, due mainly to decreased baseline variability (p<0.001, OR 3.57, 95% CI 1.8-6.9), but the incidence of other pathological patterns did not differ. Using the same set of criteria for interpretation, there was a higher incidence of abnormalities from continuous cardiotocogram monitoring in the preterm group compared to term labours, but the intervention rate for fetal distress was not significantly increased. Appropriate interpretative criteria for intrapartum monitoring of preterm labours should be devised.

High risk pregnancy monitored antenatally at home

OBJECTIVE

Is domiciliary antenatal fetal surveillance for selected high risk pregnancies, a feasible alternative for hospital admission?

DESIGN

A randomized controlled trial conducted at the Academical Medical Centre, Amsterdam, The Netherlands.

SUBJECTS

Between September 1992 and June 1994, 76 women were at random allocated to domiciliary care and 74 women to hospital care. Criteria for inclusion were hypertension (26%), fetal growth retardation (24%), post term pregnancy (23%), diabetes (24%), preterm rupture of membranes (2%) and previous recurrent antenatal death (1%).

MAIN OUTCOME MEASURES

Primary outcome measure was perinatal morbidity, measured by Prechtl's neonatal neurological optimality score. Secondary outcome variables were the occurrence of complications, obstetric interventions at labour, birthweight, gestational age at delivery and maternal and neonatal admission rates.

RESULTS

In both groups there was one case of perinatal mortality. In both treatment groups the median of the neurological optimality score was found at 59. Also secondary outcome variables did not show significant differences.

CONCLUSION

Domiciliary antenatal care for selected women with high risk pregnancy is feasible considering obstetric outcome.

Automated analysis of antepartum fetal heart rate in relation to fetal rest-activity states: a longitudinal study of uncomplicated pregnancies using the Sonicaid System 8000

OBJECTIVES

To learn which fetal heart rate (FHR) parameters change with gestational age and to demonstrate the relation with fetal rest-activity states.

STUDY DESIGN

FHR and fetal movements were recorded in 12 uncomplicated pregnancies from 26 weeks gestational age onwards. Seventy-two FHR recordings of 60 min duration were analysed by a computer (Sonicaid System 8000). Statistical analysis of complete 60 min recordings and selective periods of rest and activity comprised Spearman's rank correlation test, regression analysis and Wilcoxon's signed-rank test.

RESULTS

The time needed to meet the system's criteria of normality decreased with gestational age. The incidence of accelerations (ACC), overall FHR variation (VAR) and variation during 'episodes of high variation' (VEHV) increased with gestational age in the total population, but statistical significance of these relations could only be demonstrated in a minority of individual fetuses. Most FHR parameters differed significantly for periods of fetal rest and activity. No FHR parameters showed a relation with gestational age during periods of rest.

CONCLUSIONS

The increase of ACC, VAR and VEHV with gestational age is primarily due to an increase during fetal activity. The considerable variation within and between fetuses, however, can only be partly explained by fetal rest-activity states.

On intrapartum fetal monitoring

The currently advised conduct for intrapartum surveillance of the fetus is either intermittent auscultation of continuous electronic monitoring, depending on the physician's preference. This applies to all, normal or high-risk, conditions. The bases for this recommendation, a number of controlled studies comparing the two methods, showed no better neonatal outcomes and increased cesarean section rates with electronic fetal monitoring. A review of the works pertaining to fetal development of cardiovascular and central nervous systems and their response to various pathophysiologic conditions (in animals and humans) was carried out in an effort to find an explanation for this apparently uncongruous position. It was found that fetal responses to seemingly comparable conditions are radically different depending on age of gestation. Many authors have pointed this out for the human fetus. However, for interpretation of electronic fetal monitoring in labor, various standard, nondescriptive, confusing words are used to imply the need for rapid intervention. The complete lack of uniform interpretation has been shown in studies comparing interobserver and intraobserver variations. This may be the consequence of poor or superficial teaching of a tool that requires much study and hard work for useful application. The inescapable conclusion is unpleasant but inevitable: to use electronic fetal monitoring properly it is necessary to start a new learning of the physiology of the fetus, its changing evolution as pregnancy advances, its different responses under stress or distress, and the various ways these are represented in electronic fetal monitoring tracings. These efforts take dedication and time spent in labor suites collating tracings with neonatal condition. Only by doing this will it be possible to assist the laboring patients with a useful tool that, so far, has not been adequately applied because of insufficient understanding.

Fewer accelerations and decreased long term variability in the heart rate of small for gestational age fetuses

Two hundred newborns delivered after decelerative antenatal fetal heart rate tracings were divided retrospectively into two groups, one that was small for gestational age (SGA) and another that was appropriately grown for gestational age (AGA). Analysis of the tests showed a lower prevalence of good long term variability in the SGA group when compared with the AGA group. In addition, fetal heart rate accelerations occurred less frequently in the SGA group, even in the presence of good long term variability.

Determinants of perinatal outcome in pregnancy-induced hypertension with absence of umbilical artery end-diastolic frequencies

Forty-three pregnancies that were complicated by pregnancy-induced hypertension and either absence of umbilical artery end-diastolic frequencies (n = 32) or reversal of umbilical artery end-diastolic frequencies (n = 11) were reviewed. The incidence of perinatal mortality and morbidity was similar for the two Doppler patterns. Perinatal survival was highly dependent on the gestational age when hypertension first appeared. Presentation at greater than or equal to 30 weeks' gestation was associated with a perinatal survival rate of 86%. Presentation at less than 30 weeks' gestation was associated with a perinatal survival rate of 38% (p less than 0.005). Pregnancy-induced hypertension that presented before 30 weeks was more often associated with a 5-minute Apgar score less than 7 (p less than 0.005) and a nonreactive nonstress test (p less than 0.05) compared with pregnancy-induced hypertension that presented at or beyond 30 weeks. For pregnancies that presented before 30 weeks, the only difference between perinatal survivors (n = 11) and perinatal deaths (n = 18) was a higher incidence of birth weight at or below the 10th percentile among deaths (p = 0.02).

Computer-assisted analysis of normal second trimester fetal heart rate patterns

A software package for computer-assisted analysis of antenatal fetal heart rate (FHR) patterns has been commercially available from 1989. Reference ranges for the third trimester of pregnancy have been established. In order to obtain reference values for the second trimester, one hour FHR recordings were made between 20 and 29 weeks gestation in 77 women with uncomplicated pregnancies. There was a significant increase of (medium term) FHR variation and of the number of accelerations from 20 to 29 weeks (r = 0.48, p less than 0.01 and r = 0.34, p less than 0.01 respectively). The lower limit of normal FHR variation (mean--2 SD's) increased from 18 msec at 20 weeks to 28 msec at 28 weeks. Furthermore, a 30 minute recording appeared to be sufficient to obtain a reliable impression of FHR variation. Short term FHR variation, a measure of FHR variation that facilitates the identification of sinusoidal FHR patterns, also increased significantly between 20 and 29 weeks (r = 0.61, p less than 0.01). Delerations (greater than 20 beats/min and greater than or equal to 30 seconds) were present in 54% of the recordings and are a more or less common phenomenon at this age. It is concluded that during the second trimester FHR variation differs considerably from that in the third trimester. This should be taken into account in the interpretation of second trimester FHR records.

Fetal heart rate patterns in red blood cell isoimmunized pregnancies

Fetal heart rate was monitored in 33 red blood cell isoimmunized patients at 32 to 36 weeks' gestation immediately before cordocentesis. The fetal heart rate patterns were analyzed according to 25 different classifications, and the values were related to the fetal hemoglobin concentration, oxygen tension, and oxygen content. Nonreactive, suboptimal, or pathologic fetal heart rate patterns were encountered more commonly in fetuses that were hypoxemic and anemic than in those that were normoxemic and nonanemic. However, the positive predictive value of these abnormal fetal heart rate patterns with respect to fetal anemia was 50% to 100%; the negative predictive value was 18% to 40%.

Heart rate patterns in normoxemic, hypoxemic, and anemic second-trimester fetuses

Fetal heart rate monitoring was performed immediately before cordocentesis on 71 occasions on 49 patients at 20 to 26 weeks' gestation. In the normoxemic, nonanemic fetuses, the basal fetal heart rate was 120 to 160 beats/minute, the baseline variability was more than 5 beats/min, and there were no prolonged decelerations. Accelerations were present in 19 of the 25 recordings. In the tracings from the hypoxemic (n = 11) or anemic (n = 35) fetuses, there was tachycardia, baseline variability of less than 5 beats/min, and prolonged fetal heart rate decelerations. However, the sensitivity of these pathologic patterns in predicting moderate-to-severe hypoxemia or anemia was 45% and 33%, respectively. The data demonstrate a gestation-dependent maturation of both normal and pathologic fetal heart rate patterns.

The preterm nonstress test: effects of gestational age and length of study

The application of the nonstress test between 24 and 32 weeks' gestation has been limited by high rates of "false" nonreactivity in normal fetuses, by use of term criteria, and the lack of age-appropriate interpretative standards. To establish such standards, we studied 30 normal fetuses undergoing 90-minute fetal heart rate recordings at 2-week intervals from 24 to 32 weeks' gestational age. Using a specially programmed computer we quantified (1) baseline fetal heart rate, (2) incidence of 10- and 15-beat accelerations, and (3) incidence of fetal heart rate decelerations. With a criterion of three 15-beat accelerations per 30 minutes 91% of tests were reactive within 90 minutes. A criterion of three 10-beat accelerations per 30 minutes was associated with 100% reactivity within 60 minutes. Suitable interpretative criteria may be established for nonstress tests before 32 weeks' gestation by extending the testing time or by decreasing the minimum amplitude required of fetal heart rate accelerations.

Fetal responses to vibratory acoustic stimulation: influence of basal heart rate

Forty-three healthy pregnant women between 26 and 40 weeks' gestation were studied to determine the influence of prestimulation basal heart rate on the maximum amplitude of the first fetal heart rate acceleration after external vibratory acoustic stimulation. A significant negative correlation was found between the maximum amplitude of the first fetal heart rate acceleration and the prestimulation basal fetal heart rate from 30 weeks to term. In the presence of fetal tachycardia (basal fetal heart rate greater than 160 beats/min), more than 50% of fetal heart rate accelerations after stimulus were less than 15 beats/min amplitude. There was also a significant maturational process in the immediate fetal heart rate response to vibratory acoustic stimulation that occurred between 26 to 28 and 30 to 32 weeks characterized by a prolonged increase in basal fetal heart rate and an increase in the maximum amplitude of the first acceleration after stimulation.

Antepartum cardiotocography

Antepartum cardiotocography remains a valuable adjunct in the management of the high-risk gravida. Twice weekly use of NST coupled with real-time ultrasound assessment of amniotic fluid volume appear reasonable approaches to testing. More controversial is the use of testing in all pregnancies. Clearly, if one could reduce the perinatal mortality to 1-2/1000, such universal application of testing could be justified. However, more pragmatic concerns, such as personnel and cost constraints have all but prohibited the adoption of this policy. Secondly, in an attempt to improve the predictive reliability of antenatal testing additional evaluation of patients demonstrating diminished AFV or variable decelerations should be considered. More frequent testing or consideration for delivery are reasonable management plans. Finally, the use of acoustic stimulation to reduce the frequency of persistently non-reactive NSTs offers considerable promise. Investigations in this and other techniques of surveillance are ongoing. The best single method remains to be discovered, but utilization of current techniques offers the obstetrician a reliable technique by which to assess fetal well-being.