Low Fetal Heart Rate Variation Research Articles

Is lower fetal heart rate variability a susceptibility marker to the impact of negative coparenting on infant regulatory capacity?

Lower fetal heart rate variability (FHRV) may be a prenatal endophenotypic susceptibility marker and increase the impact of both positive and negative coparenting on infant regulatory capacity. This study analyzed the moderator role of FHRV in the association between positive and negative coparenting and infant regulatory capacity at 3 months. The sample comprised 86 first-born infants and their mothers and fathers recruited at a public Health Service in Northern Portugal. FHRV was recorded during routine cardiotocography examination at the third trimester of gestation. Mothers and fathers reported on coparenting and infant regulatory capacity at 2 weeks and 3 months postpartum. FHRV moderated the association between mother's and father's negative coparenting at 2 weeks postpartum and infant regulatory capacity at three months. Infants with low FHRV presented higher regulatory capacity when mothers or fathers reported less negative coparenting, while lower regulatory capacity when mothers or fathers reported more negative coparenting, than infants with high FHRV. Findings suggested lower FHRV as a prenatal endophenotypic susceptibility marker that increases the impact of negative coparenting on infant regulatory capacity.

35.1 Links Between Maternal Gestational Depression, Corticosteroids, and Fetal Heart Rate Variability: Predicting Early Markers of Infant Inhibition and Regulation

Maternal depression during gestation adversely affects fetal nervous system development and may lead to childhood behavioral problems. Mechanisms of adverse effects are less understood, although cortisol secretion is a potential mediator. Limited research has evaluated links between maternal depression, corticosteroids, and early markers of nervous system development, such as fetal heart rate variability (FHRV), cerebral inhibition, or temperament characteristics. Thus, the objectives were to: 1) evaluate associations between maternal depression, corticosteroids, and FHRV; and 2) test whether FHRV predicts markers of infant inhibition and regulatory capacity. Maternal depression and hair concentrations of cortisol and cortisone were measured during gestation. Heart rate was recorded in 23 fetuses by transabdominal Doppler. The SD of interbeat intervals over 20 minutes was computed to assess FHRV. Higher FHRV values reflect greater physiological regulation. Maternal depression, corticosteroid, and FHRV measurement occurred between 28 and 33 weeks gestation. Subsequent markers of infant nervous system development and temperament were assessed. Newborn development of cerebral inhibition was evaluated at 44 weeks gestation through an auditory sensory gating paradigm. Parents rated their infant’s temperamental regulatory capacity when infants were 3 months of age. Maternal depression was associated with lower FHRV, especially for male fetuses (β = –0.633; p = 0.045). Maternal depression was associated with lower cortisol to total corticosteroids ratios (β = –0.519; p = 0.033). Higher cortisol ratios were associated with increased FHRV (β = 0.485; p = 0.019). Higher FHRV was associated with decreased newborn sensory gating deficits (β = –0.992; p = 0.035), indicating better development of cerebral inhibition. Higher FHRV was also related to increased infant regulatory capacity (r = 0.454; p = 0.029). Maternal depression is associated via corticosteroids with decreased FHRV. Decreased FHRV predicted worse infant inhibition and infant regulatory capacity. Conclusions are limited due to the small sample size. Interventions addressing gestational depression may mitigate biologically mediated adverse effects on infants and thus need further study.

Maternal corticosteroids and depression during gestation and decreased fetal heart rate variability.

Maternal depression during gestation is an adverse factor in fetal brain development that manifests in later childhood behavioral problems. Fetal heart rate variability (FHRV) mediated by parasympathetic input is a marker of gestational nervous system development. Biological mediators of adverse effects of maternal depression may involve the mother's corticosteroids; however, links between depression, corticosteroids, and early nervous system development remain inconclusive. Heart rate was recorded in 23 fetuses by transabdominal Doppler at 28-33 weeks gestation. The SD of interbeat intervals over 20 min assessed FHRV. Maternal depression ratings and hair concentrations of cortisol and cortisone were assayed. An auditory sensory gating paradigm assessed newborn development of cerebral inhibition. Parents rated their infant's temperament characteristics on the Infant Behavior Questionnaire-Revised Short Form (IBQ-R). Maternal depression was associated with lower FHRV, especially for male fetuses, β = -0.633, P = 0.045. Maternal depression was associated with lower cortisol to total corticosteroids ratios, β = -0.519, P = 0.033. Lower cortisol ratios were associated with decreased FHRV, β = 0.485, P = 0.019. Decreased FHRV was associated with increased newborn sensory gating deficits, β = -0.992, P = 0.035, indicating poorer development of cerebral inhibition. Higher FHRV was related to increased infant IBQ-R self-regulatory behaviors, r = 0.454, P = 0.029. Maternal depression is associated via corticosteroids with decreased development of nervous system control of fetal heart rate. Decreased FHRV indicates developmental alterations in gestation that correlate with altered brain function and subsequent regulatory challenges in early infancy.

Analysis of the results of a retrospective cohort study of the course of pregnancy, childbirth and the postpartum period in high-risk patients to identify factors of unfavorable outcomes and build a predictive model of fetal loss

Prenatal prognosis is an important part of obstetric care, which aims to reduce fetal and neonatal losses. A differentiated approach to the management of different risk groups allows you to optimize existing approaches.The objective: to identify antenatal factors that correlate with perinatal losses, by conducting a retrospective cohort study of women at high perinatal risk, to build a multifactorial prognostic model of adverse pregnancy outcomes.Materials and methods. A retrospective cohort study was conducted from 2014 to 2016 on the basis of the medical center LLC «Uniclinic», Medical Genetics Center «Genome», Clinic of Reproductive Genetics «Victoria», Kyiv City Maternity Hospital №2. 2154 medical cards of pregnant women from the group of high perinatal risk were selected and analyzed. Of these, 782 pregnant women were included in the final protocol after verification of compliance with the criteria.Results. Cesarean delivery occurred in 115 cases (14.7%). In 50 cases (6.4%) the caesarean section was performed in a planned manner, in 65 (8.3%) – in an emergency. In 39 (5%) cases, the indication for surgical delivery was acute fetal distress. Antenatal fetal death occurred in 11 (1.4%) cases: one case in terms of <34 weeks and <37 weeks of gestation, the remaining 9 cases – in terms of> 37 weeks. Intranatal death of two fetuses (0.3%) was due to acute asphyxia on the background of placental insufficiency. In the early neonatal period, 14 (1.8%) newborns died. Hospitalization of the newborn to the intensive care unit for the first 7 days was registered in 64 (8.2%) cases.The need for mechanical ventilation was stated in 3.96% (31/782) of newborns. The method of construction and analysis of multifactor models of logistic regression was used in the analysis of the relationship between the risk of perinatal losses (antenatal death, intranatal death, early neonatal death) and factor characteristics.Conclusion. Signs associated with the risk of perinatal loss: the presence of chronic hypertension, preeclampsia in previous pregnancies, type of fertilization (natural or artificial), the concentration of PAPP-A (MoM), the concentration of free β-HCG (MoM) in the second trimester, average PI in the uterine arteries in 28–30 weeks of pregnancy, PI in the middle cerebral arteries in 28–30 weeks of pregnancy, episodes of low fetal heart rate variability in the third trimester of pregnancy, episodes of high fetal heart rate variability in the third trimester of pregnancy. The model, built on selected features, allows with a sensitivity of 73.1% (95% CI: 52.2% – 88.4%) and a specificity of 72.7% (95% CI: 69.3% – 75.9%) to predict risk perinatal loss.

Higher maternal weight is related to poorer fetal autonomic function.

Maternal obesity is an established risk factor for poor infant neurodevelopmental outcomes; however, the link between maternal weight and fetal development in utero is unknown. We investigated whether maternal obesity negatively influences fetal autonomic nervous system (ANS) development. Fetal heart rate variability (HRV) is an index of the ANS that is associated with neurodevelopmental outcomes in the infant. Maternal-fetal magnetocardiograms were recorded using a fetal biomagnetometer at 36 weeks (n = 46). Fetal HRV was represented by the standard deviation of sinus beat-to-beat intervals (SDNN). Maternal weight was measured at enrollment (12-20 weeks) and 36 weeks. The relationships between fetal HRV and maternal weight at both time points were modeled using adjusted ordinary least squares regression models. Higher maternal weight at enrollment and 36 weeks were associated with lower fetal HRV, an indicator of poorer ANS development. Further study is needed to better understand how maternal obesity influences fetal autonomic development and long-term neurodevelopmental outcomes.

Maternal abuse history and reduced fetal heart rate variability: Abuse-related sleep disturbance is a mediator.

The consequences of childhood maltreatment are profound and long lasting. Not only does the victim of abuse suffer as a child, but there is mounting evidence that a history of maltreatment places the next generation at risk for significant psychopathology. Research identifies postnatal factors as affecting this intergenerational transmission of trauma. However, emerging evidence suggests that part of this risk may be transmitted before birth, passed on via abuse-related alterations in the in utero environment that are as yet largely unidentified. To date, no study has directly assessed the influence of pregnant women's abuse history on fetal neurobehavioral development, nor considered trauma-associated poor sleep quality as a mediator reflecting established physiological dysregulation. Using data from 262 pregnant adolescents (ages 14-19), a population at elevated risk for childhood maltreatment, the current study examined maternal emotional abuse history and sleep quality in relation to third-trimester fetal resting heart rate variability, an index of parasympathetic nervous system functioning. The results indicate that maternal emotional abuse history is indirectly associated with lower fetal heart rate variability via abuse-related sleep disturbances. These data demonstrate an association between maternal abuse histories and fetal development, showing that at least part of the intergenerational transmission of risk occurs during pregnancy.

Deficient maternal zinc intake—but not folate—is associated with lower fetal heart rate variability

ObjectiveFew studies of maternal prenatal diet and child development examine micronutrient status in relation to fetal assessment. MethodsTwenty-four-hour dietary recall of zinc and folate and 20min of fetal heart rate were collected from 3rd trimester pregnant adolescents. ResultsDeficient zinc was associated with less fetal heart rate variability. Deficient folate had no associations with HRV. Neither deficient zinc nor deficient folate was related to fetal heart rate. ConclusionsThese findings, from naturalistic observation, are consistent with emerging data on prenatal zinc supplementation using a randomized control design. Practical ImplicationTaken together, the findings suggest that maternal prenatal zinc intake is an important and novel factor for understanding child ANS development.

Computerized analysis of acute and chronic changes in fetal heart rate variation and fetal activity in association with maternal smoking

Objective: To investigate the acute and chronic changes in fetal heart rate and fetal activity in association with maternal smoking by means of a computerized fetal behavior assessment program. Study Design: In 13 term nonsmokers and 13 term smokers, fetal behavior was analyzed for 2 consecutive periods of >60 minutes. In between these 2 periods, the smokers were allowed to smoke 1 cigarette, the nonsmokers were allowed a short break of comparable time span. Fetal heart rate variation and fetal activity were recorded by a single 1.5-MHZ ultrasound transducer. The percentage of time spent in low and high fetal heart rate variation and fetal activity were analyzed by computer before and after the short break for nonsmokers and before and after the smokers smoked the 1 cigarette. Smoking-induced changes in Doppler umbilical artery recordings were also investigated. Chronic exposure to cigarette smoke was objectively evaluated by measuring the carbon monoxide concentration in expired air in all participating women after breath holding. Results: Fetuses chronically exposed to cigarette smoke spent significantly more time in a low fetal heart rate variation pattern, while fetal activity was decreased both in high and low fetal heart rate variation periods. After maternal smoking, no acute changes were observed in fetal heart rate variation, yet a reduction in fetal activity was noted; however, this only reached statistical significance in periods of high fetal heart rate variation. No significant change in mean fetal heart rate was observed, yet a significant reduction in the frequency of accelerations was noted. Smoking caused an acute and transient increase in the mean pulsatility index in the umbilical artery. Conclusion: The computer program was able to detect changes in fetal behavioral variables in association with acute and chronic smoking. These changes may be suggestive of altered neurodevelopmental maturation possibly resulting from chronic fetal hypoxemia. This computer program offers a real possibility that analysis of fetal behavioral variables can be brought into routine clinical practice. Incorporating an analysis of these behavioral variables into smoking cessation programs may render them more successful. (Am J Obstet Gynecol 2001;185:421-6.)

Fetal heart rate in relation to its variation in normal and growth retarded fetuses

Objectives: (1) to assess the relationship of basal fetal heart rate (FHR) with both long term (LTV) and short term (STV) FHR variation in low-risk pregnancies, longitudinally from 24 weeks gestation onwards and (2) to investigate the relationship of FHR with LTV and STV in intrauterine growth retarded (IUGR) fetuses. Study design: Computerised FHR recordings were made in twenty-nine uncomplicated pregnancies ( n=224) and in twenty-seven IUGR fetuses who were selected retrospectively from three databases ( n=135). Nomograms of FHR variation with FHR and GA were constructed using multilevel analysis. Results and conclusions: There was a strong negative relationship of FHR with both LTV and STV in the control group ( R 2=53% and 52%, respectively). In the IUGR fetuses, FHR was generally higher than in normal fetuses whereas LTV and STV were lower. The relationship of FHR with LTV and STV in the IUGR group was less strong (for both: R 2=18%). Correction of FHR variation for basal FHR in the IUGR fetuses only resulted in a slight reduction in the number of recordings with a variation below the normal range. As it does not improve the recognition of fetuses being considered at the highest risk, such a correction of FHR variation for basal FHR is therefore not necessary. Intrafetal consistency, known to be present in healthy fetuses, was also present in the IUGR fetuses with a low FHR variation.

Computerised analysis of behaviour in normal and growth-retarded fetuses

Fetal behaviour [fetal heart rate (FHR) variation and movements (FA)] was studied in 27 normally grown fetuses and in 18 fetuses with intrauterine growth restriction (IUGR). FHR and FA were recorded using a single 1.5 MHz ultrasound transducer and analyzed by computer. The IUGR fetuses had significantly lower FA rates than the normally grown fetuses at all gestation times. They also spent a significantly lower proportion of time exhibiting high FHR variation at 28–31 weeks. Only two of the eighteen IUGR fetuses had abnormal biophysical profile scores (BPS) at the time of recording and yet all but one of them had either FHR or FA patterns that were outside the 10–90th centile range for the normally grown fetuses, suggesting that FHR and FA abnormalities predated BPS changes. More of the IUGR fetuses had abnormalities of FA than FHR. Finally, within the IUGR fetuses, those with small head circumferences (less than 3rd centile) had lower FA rates during periods of both low and high FHR variation, though this was only statistically significant for periods of low FHR variation ( P<0.05). This preliminary study offers the possibility that such objective evaluation of fetal behaviour could be used in a clinical setting and provide a more sensitive method of fetal assessment than the BPS.

Noninvasive monitoring of fetal heart rate during the last ten days of gestation in sows

SUMMARY Objective To develop and evaluate a noninvasive technique for monitoring and analyzing porcine fetal heart rate (FHR) during late gestation. Animals 8 fetuses of 8 pluriparous sows in late gestation. Procedure With the sow positioned in lateral recumbency, the most caudal fetus was identified, using real time ultrasonography, and its heart rate was recorded for 60 minutes by use of Doppler cardiography. The same fetus was identified and monitored repeatedly during the last 10 days of gestation, excluding the 24 hours before delivery. Visual inspection and computerized analysis of the recordings were performed. Results 66 one-hour recordings were obtained from 8 fetuses, 1 in each of 8 sows. Mean signal loss was 37.5%. Episodes of low FHR and low FHR variation (FHR pattern A) alternated with episodes of high FHR and high FHR variation (FHR pattern B). This cyclic alternation between 2 distinct FHR patterns was observed in 46 of 66 (69.7%) recordings, and suggests the presence of different behavioral states in fetal pigs. Basal FHR decreased toward parturition in 7 fetuses, but increased in 1 fetus with abdominal ascites. Basal FHR and long-term FHR variation were negatively correlated (r[S) = −0.73; P &lt; 0.001). Conclusion Noninvasive monitoring of FHR is possible and feasible during late gestation in pigs. This method permits longitudinal studies under pathophysiologic conditions and the evaluation of the effects of endogenous and exogenous influences on porcine FHR. (Am J Vet Res 1997;58:1285–1290)

The intrapartum CTG prior to neonatal encephalopathy at term: a case-control study.

To compare cardiotocograph (CTG) records during labour in cases of neonatal encephalopathy and matched controls. Case-control study. Metropolitan area of Perth, Western Australia. Term deliveries complicated by neonatal encephalopathy and controls matched for sex, hospital, time of birth, day of week of birth and maternal health insurance. Low fetal heart rate (FHR) variability, FHR accelerations, late decelerations, total Kreb's score and FIGO classification of CTG records. The neonatal encephalopathy group had significantly more abnormal CTG records (89%) classified according to FIGO, although 52% of control CTG records were also abnormal. CTG records from cases developed significant differences in terms of absence of FHR accelerations and low FHR variability, but not late decelerations, prior to delivery. Given the low incidence of neonatal encephalopathy in this study (7 per 1000) the predictive value of an abnormal CTG record is clinically unhelpful. However, the changes in the FHR in such cases suggest a greater disturbance of fetal (rest-activity) behaviour during labour.

Antepartum vibroacoustic stimulation in patients with low fetal heart rate variability

Objective: The purpose of this study was to examine the effect of vibroacoustic stimulation during low fetal heart rate (FHR) variability. Methods: FHR was analyzed 30 min before and 30 min after computerized vibroacoustic stimulation using the Oxford Sonicaid system 8000. The study comprised 32 healthy pregnant women with low antepartum FHR variability. The significance of difference of the median values was examined using Wilcoxon's matched-pairs signed-ranks test. Results: Vibroacoustic stimulation of the fetus during low FHR variability evoked a significant increase in the number of accelerations (>10 bpm) and an increase in long- and short-term variation. Conclusion: Our findings indicate that vibroacoustic stimulation during low FHR variability produces an abrupt change from a quiet to an active fetal state.

Is fetal heart rate variability a good predictor of fetal outcome?

The purpose of this study was to investigate, in a prospective manner, whether fetal heart rate (FHR) variability serves as a reliable single predictor of fetal outcome. We undertook a prospective study of 2,200 consecutive deliveries. Preterms < 37 weeks, twins, stillbirths and fetal malformations were excluded from the study. FHR tracings were analyzed for variability in every delivery. Three windows were evaluated: 1) early in labor (30 min); 2) in the active phase of labor - 1 h prior to complete cervical dilatation (30 min); and 3) throughout the second stage of delivery, in segments of 30 min. Using the tracings taken at admission and prior to delivery, FHR variability was scored according to five previously used evaluative methods, and was correlated to the following three fetal outcome parameters: a) arterial cord blood pH < 7.2, > 7.2; b) 5-min Apgar >6, < 7; and c) immediate outcome ('good' defined as newborn going home after 2-5 days, with no neonatal intensive care unit (NICU) admission). 1. The majority of cases with adverse fetal outcome exhibited good FHR variability (mean, 80%). 2. Low FHR variability is not common in newborns with adverse general outcome (mean, 11.5%). 3. The predictability of FHR variability (using the five most common scoring methods) for evaluating adverse fetal outcome revealed low sensitivity (mean, 20.3%) and low predictive value (mean, 11.6%). FHR variability by itself cannot serve as the only indicator of fetal wellbeing. The presence of low variability should alert the physician; however, good FHR variability should not be interpreted as reassuring.

Response of the premature fetus to stimulation by speech sounds

The response of the premature fetus to speech stimuli was studied in 41 healthy pregnant patients at 26–34 weeks gestation. Speech stimuli consisted of repeated syllables (‘ee’ and ‘ah’) presented externally over the maternal abdomen at either 100, 105, or 110 decibels (dB). Sound stimuli were delivered during periods of both high and low fetal heart rate variability. During periods of low FHR variability, a decrease in fetal heart rate and an increase in the standard deviation of heart rate were found. During periods of high FHR variability, no significant change in either of these measures was observed. This is the first clear demonstration of heart rate responses to speech stimuli in the premature fetus. As is the case in the term fetus, this response is dependent on baseline heart rate variability which is the primary determinant of fetal state. The clinical usefulness of this finding may be limited by the magnitude of the response.

Large fetal heart rate decelerations at term associated with changes in fetal heart rate variation

The objective was to determine whether large antepartum decelerations in fetal heart rate were associated with a switch from high to low fetal heart rate variation, suggestive of a change in sleep state, and whether the variation predicted outcome. Retrospective computerized analysis of 10,272 cardiotocographic records from 3998 patients at 37 to 42 weeks' gestation from four centers in England and Italy identified 140 good-quality records with large decelerations (more than 20 lost beats in area). In otherwise normal cardiotocograms a large deceleration had a 40% chance of association with a downward change in fetal heart rate variation (69% when the deceleration exceeded 100 lost beats). The change resembled that occurring naturally with behavioral states. Uterine contractions did not always precede large decelerations. When they did, the lag time (peak of contraction-trough of deceleration) increased from 28 seconds (at 20 to 29 lost beats) to > 100 seconds with increase in deceleration area. Of patients with large decelerations 76% had a normal vaginal delivery. Large decelerations near term, present in up to 5% of patients with otherwise normal fetal heart rate and variation, are often associated with a fall in fetal heart rate variation characteristic of a change in sleep state, without ominous significance.

Vibro-acoustic stimulation does not alter the duration of high and low fetal heart rate variability episodes.

To study the effect of vibro-acoustic stimulation on high and low fetal heart rate (FHR) variability episodes. Prospective control study, in 21 high risk pregnancies between 32 to 39 weeks gestation. FHR pattern was recorded with cardiotocograph (CTG). After 5 min low FHR variability a vibro-acoustic stimulator was activated in contact with or above the maternal abdomen (sham) on a random basis on two consecutive days, and CTG was continued to obtain a complete high and low FHR variability cycle. Complete high and low FHR variability cycles were obtained in 12 patients with mean recording time of 129.5 minutes (range 69-185 min). The mean baseline FHR increased by 32.5 +/- 9.4 bpm after contact vibro-acoustic stimulation, but remained unchanged after sham stimulation. Mean duration of high FHR variability was 56.6 +/- 32.9 min and 47.3 +/- 23.7 min, respectively, and mean duration of the consecutive low FHR variability episode was similar after contact and sham stimulation. The complete cycles were 71.1 +/- 34.7 min and 66.2 +/- 21.2 min, respectively. Vibro-acoustic stimulation induced an abrupt change from low to high FHR variability, but the complete cycle of high and low FHR variability was not altered, when compared with the corresponding cycle following sham stimulation on the same fetus.

Computerised cardiotocography following vibro-acoustic stimulation.

To study the effect of vibro-acoustic stimulation (VAS) to the mean fetal heart rate (FHR), period of high and low FHR variation, overall variation (msec and bpm) and short term variation (msec). In a prospective study 17 pregnant women between 34-42 weeks gestation admitted to antenatal ward for obstetric complications two 60 min FHR recording was carried out with an interval of 30 min in between recordings. On a random basis the fetus was stimulated by a vibro-acoustic stimulator for 5 sec at the beginning of one of the two 60 min FHR recordings. Automated analysis of the FHR, tocodynamometry, and maternal perception of fetal movements was done by a commercially available computerized programme (System 8000). It was possible to obtain the two 60 min recordings with signal loss of < 10% in 12 out of 17 patients. No changes were observed when the FHR parameters for 60 min after VAS was compared with the control period. When analyzed in segments of 0 to 10, 11 to 20, 20 to 40 and 41 to 60 min the mean baseline FHR was significantly higher after VAS during the first 10 minutes compared with any 10 or 20 min segment of the control period or any such segments 10 min after VAS. Concomitantly the overall variation and short-term variation was significantly lower during the first 10 minutes following VAS (p < 0.05) compared with the parameters in the corresponding periods during the control period.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal heart rate response to vibroacoustic stimulation during low and high heart rate variability episodes in late pregnancy

In 52 women in late pregnancy, the mean durations of transient fetal tachycardia after vibroacoustic stimulation during low fetal heart rate variability (4.8 minutes) and high fetal heart rate variability (6.3 minutes) were similar. The fetal heart rate continued with high variability in all cases, suggesting that the fetus did not return to its prestimulation state after vibroacoustic stimulation during quiescence. In 10 women, the duration of high variability after vibroacoustic stimulation during low fetal heart rate variability was significantly shorter (mean, 22 minutes) than the preceding (mean, 36 minutes) or subsequent (mean, 43 minutes) high-variability components of complete rest activity cycles. In another 10 women, the duration of high variability after vibroacoustic stimulation during high fetal heart rate variability was similar to preceding and subsequent high-variability episodes. In these 20 women, the next complete rest-activity cycle after vibroacoustic stimulation was not different in duration to the complete cycle recorded on the previous day.

Automated analysis of near-term antepartum fetal heart rate in relation to fetal behavioral states: The Sonicaid System 5000

Fetal heart rate and fetal movements were recorded in 16 uncomplicated near-term pregnancies. The recordings were used to evaluate a system for automated fetal heart rate analysis (Sonicaid System 8000). Fetal rest-activity patterns were considered in the analysis. The mean duration of C2F periods "active sleep," 33 minutes) was significantly greater than that of C1F periods ("quiet sleep," 19 minutes) (p less than 0.001). The incidence of accelerations and decelerations and the overall fetal heart rate variations were greater during C2F than during C1F (p less than 0.001). In 11 of 16 C1F periods, the system classified the fetal heart rate variation as "questionable" or "abnormal." Episodes of high variation were identified in only 3 of 16 C1F periods, but they were found in all 18 C2F periods. Episodes of low variation were identified in 14 of the 16 C1F periods but were not found in any C2F periods. During C2F periods, the system's criteria of normality were met in all cases but one; they were not met during any of the C1F periods. Thus the diagnosis of fetal distress should not be based merely on the absence of accelerations, low fetal heart rate variation, or absence of episodes of high variation in recordings with a duration of less than 45 minutes.