The prevalence, aetiology and clinical significance of pseudo-sinusoidal fetal heart rate patterns in labour.

OBJECTIVE--To investigate the prevalence of sinusoidal and pseudo-sinusoidal fetal heart rate (FHR) patterns in labour and the relation between the characteristics of the FHR pattern and fetal outcome. DESIGN--A prospective observational study over a 6-month period in which all women who had continuous FHR monitoring in labour had their intrapartum cardiotocographs (CTGs) scrutinized for the presence of sinusoidal or pseudo-sinusoidal FHR patterns. SETTING--John Radcliffe Hospital, Oxford. SUBJECTS--1520 women who had fetal monitoring during labour for various reasons. MAIN OUTCOME MEASURES--Both internal (electrocardiographic) and external (ultrasound) recordings of the FHR were analysed. Abnormal FHR patterns were related to obstetric characteristics and fetal outcome in terms of Apgar scores, umbilical artery pH and admission to the special care unit. RESULTS--No true sinusoidal FHR patterns were observed, but pseudo-sinusoidal FHR patterns were found in 230 of the 1520 CTGs examined (15%). Of these, 219 were classified as minor (amplitude 5-15 beats/min) and 11 as intermediate (amplitude 16-24 beats/min). Major pseudo-sinusoidal FHR patterns (amplitude greater than 24 beats/min) were not observed. Minor pseudo-sinusoidal FHR patterns had a mean duration of 21 (SD 13) min and typically occurred once or twice early in labour. Using logistic regression analysis a significant, independent relation was demonstrated between the presence of minor pseudo-sinusoidal FHR patterns and the use of pethidine (RR 1.84, 95% CI 1.3 to 2.59, P less than 0.0001) and epidural analgesia (RR 1.85, 95% CI 1.24 to 2.76, P less than 0.001). Intermediate pseudo-sinusoidal FHR patterns were found in association with both in utero fetal sucking and transient episodes of fetal hypoxia such as that caused by periodic umbilical cord compression. CONCLUSION--Pseudo-sinusoidal FHR patterns in labour will usually be associated with a normal fetal outcome but a careful fetal assessment is mandatory.     

Progression in response patterns of fetal heart rate throughout labour.

A study of 70 fetal heart rate (FHR) traces throughout labour has allowed analysis of FHR responses associated with approximately 7000 individual uterine contractions. The significance of the less emphasized FHR patterns has been assessed and an attempt has been made to identify any trend or progression in the occurrence of these patterns. Transient acceleration was the most frequently occurring response in early labour and was the first observed response in the majority of cases. Decelerations became prevalent as labour progressed. A hypothesis is proposed to explain the observed overall progression in FHR responses and the possible physiological mechanisms underlying the cyclic changes in response patterns which occur throughout the course of labour.     

Screening of the fetal heart rate in early labour

Summary. The fetal heart rates (FHR) of 588 women admitted in labour, or in early labour after induction, were screened for up to 60 min (average 17 min) using computerized numerical analysis. Decelerative records with normal FHR variation occurred in eight (1.4%) and were not associated with acidaemia or depression at birth. Forty women (6.8%) had fetuses with a reduced FHR variation. They were more likely to be in spontaneous labour, to be at an earlier gestational age, and to be delivered operatively for fetal distress of babies that were more hypoxaemic and acidaemic. However, none of the fetuses with the least variable FHR patterns required resuscitation at birth or special care. The results of the screening procedure were not fully concealed and could have influenced clinical management. This is unlikely to have caused the associations that were observed, but could have reduced an association between low FHR variation and poor outcome. We conclude that there is a basis for a randomized controlled trial of FHR screening in early labour, but that this would need to be large (more than 10 000 patients) to test the benefit of detecting the most sinister pattern (decelerations with reduced variation) of which only one example was found in this study.     

Screening of the fetal heart rate in early labour

The fetal heart rates (FHR) of 588 women admitted in labour, or in early labour after induction, were screened for up to 60 min (average 17 min) using computerized numerical analysis. Decelerative records with normal FHR variation occurred in eight (1.4%) and were not associated with acidaemia or depression at birth. Forty women (6.8%) had fetuses with a reduced FHR variation. They were more likely to be in spontaneous labour, to be at an earlier gestational age, and to be delivered operatively for fetal distress of babies that were more hypoxaemic and acidaemic. However, none of the fetuses with the least variable FHR patterns required resuscitation at birth or special care. The results of the screening procedure were not fully concealed and could have influenced clinical management. This is unlikely to have caused the associations that were observed, but could have reduced an association between low FHR variation and poor outcome. We conclude that there is a basis for a randomized controlled trial of FHR screening in early labour, but that this would need to be large (more than 10,000 patients) to test the benefit of detecting the most sinister pattern (decelerations with reduced variation) of which only one example was found in this study.     

Clinical significance of fetal heart rate patterns during labor: IV. Agonal patterns

The characteristics of fetal heart rate (FHR) patterns were reviewed in 11 cases where the infants died either intrapartum or within eight hours of birth as a consequence of distress during labor without prior recovery. The neonatal charts and the autopsy reports were also reviewed. The infants were grouped according to gestational age as premature (four), term (four), and postmature (three). Similarities and differences were studied in an attempt to delineate some common underlying factors. The premature fetuses have an extraordinary capacity to withstand clinical signs of severe distress (late deceleration and fixed and tachycardic base line) for many hours until the very moment of death and rarely pass meconium. The term fetuses can withstand less prolonged periods of severe distress, the fixed FHR base line and impressive decelerations preceding immediate death; they consistently passed meconium, three of four had aspirated meconium. All of the postterm fetuses had massive meconium aspiration, but the FHR patterns had a bizarre appearance; several hours before death some late decelerations were followed by tachycardia and fixed base lines but no decelerations. Subsequent occurrence of erratic severe decelerations immediately preceded sudden death. Possible reasons for these different pathophysiologic responses are discussed. In the study of FHR tracings, a variable of utmost importance is chronologic age of gestation. Its value cannot be overemphasized for an accurate interpretation of the fetal condition and good decisions for management.     

Sinusoidal fetal heart rate pattern: Its definition and clinical significance

A review was made of the available literature on the sinusoidal heart rate (SHR) pattern. A specific definition of SHR was made in order to elucidate its clinical significance. According to this definition, 41 tracings from 23 publications were classified as being either true SHR, equivocal, or a heart rate pattern other than SHR. On the basis of this definition, 27 tracings were classified as true SHR patterns and all were associated with significant fetal or neonatal morbidity or mortality, except in two cases after administration of alphaprodine. Three tracings were judged to be equivocal. In two other cases the fetal heart rate tracings were classified as nonsinusoidal premortem patterns associated with poor perinatal outcome. As for the other nine tracings that did not meet the proposed definition, the perinatal outcome was normal. Therefore, because of a stricter definition of SHR as proposed in this report, the pattern appears to indicate significant fetal and/or neonatal jeopardy, except when the SHR pattern appears after induction of analgesia with alphaprodine.     

Clinical significance of fetal heart rate patterns during labor. I. Baseline patterns.

From a population of 2,774 high-risk patients monitored during labor, 1,304 single pregnancies in cephalic presentation and with direct monitoring for at least 1 hour before completion or cesarean-section were studied. The maternal and fetal clinical data and the tracings were hand reviewed, coded, and programmed for computer analysis. In the record were studied baseline, its changes (tachycardia, fixed, saltatory), the accelerations, and the decelerations (early, variable, late). Fifty-four per cent had some type of FHR deceleration. Accelerations were recorded in over 12 per cent of all cases and were associated with cord problems in 41 per cent. Subgrouping the patients by age of gestation (less than or equal to 36 weeks, 37 to 41 weeks, and greater than or equal to 42 weeks) revealed a 10 per cent prolonged gestation rate and only 6.8 per cent premature; these had a lower 5 minute Apgar score. Fetal weight and age were positively correlated with Apgar score. Baseline changes were much frequent among pre- and postmature infants, particularly tachycardia in the latter (40 per cent). The premature infants had a 25 per cent incidence of fetal distress and the postmature infants had 20 per cent. Neonatal morbidity and mortality rates were very high among premature infants and a mortality rate of 2.3 per cent was found among postmature infants. Saltatory pattern and particularly fixed baseline seem characteristic of prolonged gestation and placental insufficiency. With tachycardia, they constitute subtle symptoms of fetal distress.     

The relevance of antenatal and intrapartum fetal heart rate patterns to fetal outcome

Antenatal fetal heart rate (FHR) as an indicator of fetal status was evaluated in two separate studies. The first attempted to determine, in 30 minutes of continuous recording from each of 50 antenatal patients, relationships between spontaneous FHR changes and fetal condition before and after birth. No significant association was found between observed FHR patterns and antenatal or neonatal fetal status. The second study used induction of labour as a stress test, because similar conditions to that required for oxytocin stress testing were present and there was the advantage of direct FHR recording. In 150 induced and monitored labours, FHR changes associated with the first six suitable contractions seldom related to Apgar scores at birth or development of fetal distress in active labour. Fetuses showing no response to contractions tended to have better Apgar scores than those which showed FHR decelerations. Results from these studies do not substantiate reports that FHR changes arising spontaneously, or in response to induced contractions, reflect satisfactorily the existing or subsequent fetal status.     

The relationship between antepartum fetal heart rate, intrapartum fetal heart rate, and fetal acid-base status

The relationships between antepartum baseline fetal heart rate, baseline variability, accelerations, decelerations, and fetal movement and intrapartum fetal heart rate, fetal acid-base assessment at delivery, and Apgar scores 1 and 5 minutes after delivery were studied in 290 mature pregnancies. There was a significant relationship between antepartum and intrapartum baseline fetal heart rate and baseline variability. There was no relationship between antepartum and intrapartum accelerations or decelerations. There was no correlation between antepartum fetal heart rate or fetal movement and fetal acid-base status at delivery or Apgar scores 1 and 5 minutes after delivery. There was a trend for decreased accelerations and decreased fetal movements to be associated with a low Apgar score 1 minute after delivery.     

The effect of membrane rupture on fetal heart rate in induced labour.

The influence of the state of the membranes on the fetal heart rate was studied in a group of twelve women whose membranes were electively ruptured for oxytocin induction of labour. The results have been compared with a group of eight women of similar gestation and parity whose membranes were kept intact. While membranes were ruptured, there was an increase in the frequency and amplitude of early decelerations thorughout labour. The significance and practical implications of the results are discussed.     

Abnormal fetal heart rate patterns and placental inflammation

Can acute inflammation in the placental membranes, amniotic fluid, or both, predispose to the development of abnormal fetal heart rate patterns? One hundred cases in which bradycardia was noted were compared with 48 cases in which abnormal fetal heart rate patterns did not occur. Case and control subjects were matched to provide an equivalent risk of developing ascending infection in the two groups. Fetoplacental weight ratio and the presence of other placental diseases were also considered. The presence of acute inflammation in the umbilical cord (p = 0.03), amnion (p = 0.01), and choriodecidua (p = 0.03), and higher grades of inflammation in chorionic plate (p = 0.03) were linked to the presence of abnormal fetal heart rate patterns. No other placental factors were associated with increased risk of fetal bradycardia. The association of abnormal fetal heart rate patterns with acute inflammation suggests that intra-amniotic inflammation is important in the genesis of fetal bradycardias. The inflamed amniotic fluid could alter fetal metabolism via effects on the pulmonary or gastrointestinal systems or effects on umbilical and chorionic vessels.