Circadian changes and sex-related differences in fetal heart rate parameters

Circadian patterns of heart rate variability in fetal sheep after hypoxia-ischaemia: A biomarker of evolving brain injury

Hypoxia-ischaemia (HI) before birth is a key risk factor for stillbirth and severe neurodevelopmental disability in survivors, including cerebral palsy, although there are no reliable biomarkers to detect at risk fetuses that may have suffered a transient period of severe HI. We investigated time and frequency domain measures of fetal heart rate variability (FHRV) for 3 weeks after HI in preterm fetal sheep at 0.7 gestation (equivalent to preterm humans) until 0.8 gestation (equivalent to term humans). We have previously shown that this is associated with delayed development of severe white and grey matter injury, including cystic white matter injury (WMI) resembling that observed in human preterm infants. HI was associated with suppression of time and frequency domain measures of FHRV and reduced their circadian rhythmicity during the first 3 days of recovery. By contrast, circadian rhythms of multiple measures of FHRV were exaggerated over the final 2 weeks of recovery, mediated by a greater reduction in FHRV during the morning nadir, but no change in the evening peak. These data suggest that the time of day at which FHRV measurements are taken affects their diagnostic utility. We further propose that circadian changes in FHRV may be a low-cost, easily applied biomarker of antenatal HI and evolving brain injury. KEY POINTS: Hypoxia-ischaemia (HI) before birth is a key risk factor for stillbirth and probably for disability in survivors, although there are no reliable biomarkers for antenatal brain injury. In preterm fetal sheep, acute HI that is known to lead to delayed development of severe white and grey matter injury over 3 weeks, was associated with early suppression of multiple time and frequency domain measures of fetal heart rate variability (FHRV) and loss of their circadian rhythms during the first 3 days after HI. Over the final 2 weeks of recovery after HI, exaggerated circadian rhythms of frequency domain FHRV measures were observed. The morning nadirs were lower with no change in the evening peak of FHRV. Circadian changes in FHRV may be a low-cost, easily applied biomarker of antenatal HI and evolving brain injury.

Fetal growth restriction and stillbirth: Biomarkers for identifying at risk fetuses

Fetal growth restriction (FGR) is a major cause of stillbirth, prematurity and impaired neurodevelopment. Its etiology is multifactorial, but many cases are related to impaired placental development and dysfunction, with reduced nutrient and oxygen supply. The fetus has a remarkable ability to respond to hypoxic challenges and mounts protective adaptations to match growth to reduced nutrient availability. However, with progressive placental dysfunction, chronic hypoxia may progress to a level where fetus can no longer adapt, or there may be superimposed acute hypoxic events. Improving detection and effective monitoring of progression is critical for the management of complicated pregnancies to balance the risk of worsening fetal oxygen deprivation in utero, against the consequences of iatrogenic preterm birth. Current surveillance modalities include frequent fetal Doppler ultrasound, and fetal heart rate monitoring. However, nearly half of FGR cases are not detected in utero, and conventional surveillance does not prevent a high proportion of stillbirths. We review diagnostic challenges and limitations in current screening and monitoring practices and discuss potential ways to better identify FGR, and, critically, to identify the “tipping point” when a chronically hypoxic fetus is at risk of progressive acidosis and stillbirth.

Fetal heart rate during maternal sleep

Despite prolonged and cumulative exposure during gestation, little is known about the fetal response to maternal sleep. Eighty-four pregnant women with obesity (based on pre-pregnancy BMI) participated in laboratory-based polysomnography (PSG) with continuous fetal electrocardiogram monitoring at 36 weeks gestation. Multilevel modeling revealed both correspondence and lack of it in maternal and fetal heart rate patterns. Fetal heart rate (fHR) and variability (fHRV), and maternal heart rate (mHR) and variability (mHRV), all declined during the night, with steeper rates of decline prior to 01:00. fHR declined upon maternal sleep onset but was not otherwise associated with maternal sleep stage; fHRV differed during maternal REM and NREM. There was frequent maternal waking after sleep onset (WASO) and fHRV and mHRV were elevated during these episodes. Cross-correlation analyses revealed little temporal coupling between maternal and fetal heart rate, except during WASO, suggesting that any observed associations in maternal and fetal heart rates during sleep are the result of other physiological processes. Implications of the maternal sleep context for the developing fetus are discussed, including the potential consequences of the typical sleep fragmentation that accompanies pregnancy.

Factors associated with intrapartum ZigZag pattern of fetal heart rate: A retrospective one-year cohort study of 5150 singleton childbirths

OBJECTIVES

Recent studies suggest that intrapartum ZigZag pattern of fetal heart rate (FHR) is significantly associated with cord blood acidaemia and neonatal complications. For the clinical significance of this pattern, it is mandatory that ZigZag episodes in cardiotocographic (CTG) recording are correctly identified. The aim of the present study was to examine maternal, fetal and delivery-related factors that could explain the occurrence of ZigZag pattern of FHR during the last 2 h of labour in a large obstetric cohort.

STUDY DESIGN

CTG recordings from 5150 singleton childbirths at ≥33 weeks of gestation during one year were evaluated retrospectively and blinded to pregnancy and neonatal outcomes in a university hospital in Helsinki, Finland. All women in the cohort were in the active phase of labour with regular uterine contractions. ZigZag FHR pattern was defined as FHR baseline amplitude changes of >25 bpm with a duration of 2-30 min. The following maternal, fetal and labour/delivery-related variables were determined: maternal age, obesity (prepregnancy BMI ≥ 30.0 kg/m²), parity, preeclampsia, maternal fever ≥38.0 °C, smoking, gestational age at delivery, fetal sex, birth weight z-score, mode of delivery, and type of onset of labour.

RESULTS

ZigZag pattern occurred in 582/5150 (11.3 %) cases, and only in childbirths after 37 weeks of gestation. Fetal male gender (OR 3.29; 95 % CI 2.70-4.02), nulliparous pregnancy (OR 2.60; 95 % CI 2.15-3.15) and post-term gestational age (≥42 weeks) (OR 1.92; 95 % CI 1.47-2.48) were independently associated with the occurrence of ZigZag pattern. Among the three significant risk factors, clustering of two or three factors was associated with an increase of the ZigZag pattern occurrence risk to 5.0-16.4-fold (95 % CI 3.16-31.60).

CONCLUSIONS

ZigZag pattern occurred in term pregnancies after 37 weeks of gestation only. Fetal male gender, nulliparity and post-term pregnancy are significantly associated with ZigZag FHR pattern during the last two hours of labour. Identification of maternal, fetal and delivery-related variables are imperative in order to interpret correctly the findings of CTG and to prevent adverse neonatal outcome.

Is portable foetal electrocardiogram monitor feasible for foetal heart rate monitoring of small for gestational age foetuses in the home environment

Small-for-gestational-age (SGA) foetuses are at greater risk of complications than normal foetuses. Studies have demonstrated that foetal electrocardiogram (ECG) device (Monica-AN24) can be employed for monitoring foetal heart rate (FHR). However, its reliability and acceptability has not been assessed in SGA foetuses. This study was aimed at: (a) determining the acceptability of wearing the device more than once, (b) investigating the reliability of acquiring successful FHR data at different gestation. Patients with singleton non-anomalous foetus >24 weeks gestation and an estimated foetal weight below tenth percentile were recruited. Thirty-five women wore the device once. Twenty-four of these wore second time (68.6%). Overall, success-rate of FHR signals was 48.6% and increased to 68.8% beyond 34 weeks gestation. Foetal ECG is a promising method for monitoring SGA foetus >34 weeks gestation. Compared to day recordings, foetal signals were more reliable at night. Further studies are required before its clinical utility can be ascertained. IMPACT STATEMENT What is already known on this subject? Pregnancies that are affected by small-for-gestational-age (SGA) foetus pose a major public health problem and are associated with increased perinatal morbidity and mortality. There is no consensus on the optimal timing of delivery. Current methods employed for monitoring SGA foetuses include ultrasound scans for foetal-biometry and Doppler assessments. However, they provide a snapshot of information on foetal well-being, restrict patient mobility and cannot be employed over long-time periods. It is plausible that ambulatory foetal-ECG device that enable monitoring over a longer time period may better inform decisions about the timing of delivery. What do the results of this study add? Trans-abdominal foetal-ECG is a promising method of monitoring SGA foetus in the home setting with a success rate of acquiring reliable foetal heart rate (FHR) data over 90% at night time. What are the implications of these findings for clinical practice and/or further research? Overall, the study approved the concept of long-term home monitoring and has highlighted the facilitators and barriers to wearing the monitor in clinical care. These observations can be used to undertake robust research to assess the use of foetal-ECG monitor singly or in conjunction with current monitoring techniques for optimal foetal surveillance.

Women's experience of wearing a portable fetal-electrocardiogram device to monitor small-for-gestational age fetus in their home environment

Objective:

To determine the acceptability, to women, of wearing a portable fetal electrocardiogram recording device at different stages of pregnancy and to gain insight into their experience of its use for long-periods of monitoring of small-for-gestational fetuses in the home environment.

Methods:

A qualitative study using both a questionnaire and focus group involving women with singleton pregnancy >24 weeks gestation, no evidence of fetal malformation and an estimated fetal weight below 10th gestational centile on ultrasound scan. Fetal heart rate recordings were collected for up to 20 h.

Results:

In total, 59 questionnaires were completed; 35 after wearing the monitor for the first time and an additional 24 from the women who wore the device for a second time. Six women participated in the focus group; the principal theme identified related to the practicality of the fetal electrocardiogram device. Other themes identified were the discomfort that resulted from wearing the monitor and the reassurance provided in knowing that the baby’s heart rate was being monitored.

Conclusion:

Long-term ambulatory fetal electrocardiogram monitoring is an acceptable method of monitoring small-for-gestational fetuses. Overall, women concluded that benefits of wearing the device outweighed any discomfort it caused.

Maternal exercise, season and sex modify the daily fetal heart rate rhythm

AIM

The knowledge on biological rhythms is rapidly expanding. We aimed to define the longitudinal development of the daily (24-hour) fetal heart rate rhythm in an unrestricted, out-of-hospital setting and to examine the effects of maternal physical activity, season and fetal sex.

METHODS

We recruited 48 women with low-risk singleton pregnancies. Using a portable monitor for continuous fetal electrocardiography, fetal heart rate recordings were obtained around gestational weeks 24, 28, 32 and 36. Daily rhythms in fetal heart rate and fetal heart rate variation were detected by cosinor analysis; developmental trends were calculated by population-mean cosinor and multilevel analysis.

RESULTS

For the fetal heart rate and fetal heart rate variation, a significant daily rhythm was present in 122/123 (99.2%) and 116/121 (95.9%) of the individual recordings respectively. The rhythms were best described by combining cosine waves with periods of 24 and 8 hours. With increasing gestational age, the magnitude of the fetal heart rate rhythm increased, and the peak of the fetal heart rate variation rhythm shifted from a mean of 14:25 (24 weeks) to 20:52 (36 weeks). With advancing gestation, the rhythm-adjusted mean value of the fetal heart rate decreased linearly in females (P < .001) and nonlinearly in males (quadratic function, P = .001). At 32 and 36 weeks, interindividual rhythm diversity was found in male fetuses during higher maternal physical activity and during the summer season.

CONCLUSION

The dynamic development of the daily fetal heart rate rhythm during the second half of pregnancy is modified by fetal sex, maternal physical activity and season.

A mixed-methods evaluation of continuous electronic fetal monitoring for an extended period

INTRODUCTION

Continuous fetal monitoring is used to objectively record the fetal heart rate and fetal activity over an extended period of time; however, its feasibility and acceptability to women is currently unknown. The study addressed the hypothesis that continuous fetal monitoring is feasible and acceptable to pregnant women.

MATERIAL AND METHODS

Pregnant participants (n = 22) were monitored using a continuous fetal electrocardiography device, the Monica AN24. Signal quality, duration of recording and cardiotocography findings were correlated with maternal and fetal factors. Participants' change in anxiety before and after monitoring was assessed using validated questionnaires. Participants' experiences were explored through a questionnaire (n = 20) and semi-structured interview (n = 13).

RESULTS

Recordings were successfully obtained in 19 of the 22 participants (86.3%). The mean recording quality of fetal heart rate was 69.0% (range 17.4%-99.4%) and maternal heart rate was 99.0% (90.9%-100.0%). Recording quality was positively correlated with gestational age (P = 0.05) and negatively correlated with uterine activity and maternal movement (P < 0.001). Overall, participants were satisfied with their experience of continuous fetal monitoring; 30% considered it preferable to intermittent monitoring. Continuous fetal monitoring did not significantly increase maternal anxiety, with a trend towards a reduction in Pregnancy Specific Anxiety score (P = 0.07). Qualitative analysis grouped women's responses into three themes: (a) reassurance and anxiety, (b) the physical device and (c) future developments in continuous fetal monitoring.

CONCLUSIONS

Continuous fetal monitoring is a feasible and acceptable form of monitoring to pregnant women although further practical improvements could be incorporated. Further research is required to assess the ability of continuous fetal monitoring to detect fetal compromise.

Sex differences in fetal heart rate and variability assessed by antenatal computerized cardiotocography

INTRODUCTION

The aim of the current study is to explore the effect of fetal sex on the fetal heart rate and variability.

MATERIAL AND METHODS

This is a retrospective cross-sectional study. We analyzed fetal heart rate (FHR) traces of pregnant women that were recorded antenatally using a commercially available computerized cardiotocograph (cCTG; Oxford system). Fetal sex was ascertained after birth. Baseline FHR and short-term heart rate variation (STV) were compared between male and female fetuses. Expected mean values for baseline FHR and STV were computed and multiples of the mean (MOMean) of males and females were compared.

RESULTS

Information on 9259 cases is reported in this study. Baseline FHR of female fetuses was significantly higher (P < 0.001) and STV lower (P < 0.001) than that of male fetuses. This difference remained even after the effects of gestational age and diurnal variation were eliminated by computation of MOMean, but the absolute differences in the baseline FHR (0.9 beats/min [bpm]) and STV (0.246 ms) between male and female fetuses were small. A significant negative correlation was found between baseline FHR and STV (r = -0.518, P < 0.001). Similarly, a significant negative correlation was found between the MoMean of baseline FHR and MoMean STV (r = -0.481, P < 0.001).

CONCLUSIONS

Using the Oxford cCTG, male fetuses show a significantly lower baseline FHR and greater variability as compared with female fetuses. However, the absolute differences are small and may not be of major clinical significance.

A Comprehensive Evaluation of the Predictive Abilities of Fetal Electrocardiogram-Derived Parameters during Labor in Newborn Acidemia: Our Institutional Experience

This study aimed to identify cardiotocography patterns that discriminate fetal acidemia newborns by comprehensively evaluating the parameters obtained from Holter monitoring during delivery. Between June 1, 2015, and August 1, 2016, a prospective observational study of 85 patients was conducted using fetal Holter monitoring at the Beijing Obstetrics and Gynecology Hospital, Capital Medical University, China. Umbilical cord blood was sampled immediately after delivery and fetal acidemia was defined as umbilical cord arterial blood pH < 7.20. Fetal electrocardiogram- (FECG-) derived parameters, including basal fetal heart rate (BFHR), short-term variation (STV), large acceleration (LA), deceleration capacity (DC), acceleration capacity (AC), proportion of episodes of high variation (PEHV), and proportion of episodes of low variation (PELV), were compared between 16 fetuses with acidemia and 47 without. The areas under the curve (AUC) of receiver operating characteristics (ROC) were calculated. Although all the computerized parameters showed predictive values for acidemia (all AUC > 0.50), STV (AUC = 0.84, P < 0.001), DC (AUC = 0.84, P < 0.001), AC (AUC = 0.80, P < 0.001), and PELV (AUC = 0.71, P = 0.012) were more strongly associated with fetal acidemia. Our institutional experience suggests that FECG-derived parameters from Holter monitoring are beneficial in reducing the incidence of neonatal acidemia.

Comparison of diurnal variations, gestational age and gender related differences in fetal heart rate (FHR) parameters between appropriate-for-gestational-age (AGA) and small-for-gestational-age (SGA) fetuses in the home environment

Objective

To assess the influence of gender, time of the day and gestational age on fetal heart rate (FHR) parameters between appropriate-for-gestational-age (AGA) and small-for-gestational age (SGA) fetuses using a portable fetal ECG monitor employed in the home setting.

Methods

We analysed and compared the antenatal FHR data collected in the home setting on 61 healthy pregnant women with singleton pregnancies from 24 weeks gestation. Of the 61 women, 31 had SGA fetuses (estimated fetal weight below the tenth gestational centile) and 30 were pregnant with AGA fetuses. FHR recordings were collected for up to 20 h. Two 90 min intervals were deliberately chosen retrospectively with respect to signal recording quality, one during day-time and one at night-time for comparison.

Results

Overall, success rate of the fetal abdominal ECG in the AGA fetuses was 75.7% compared to 48.6% in the SGA group. Based on randomly selected episodes of heart rate traces where recording quality exceeded 80% we were able to show a marginal difference between day and night-time recordings in AGA vs. SGA fetuses beyond 32 weeks of gestation. A selection bias in terms of covering different representation periods of fetal behavioural states cannot be excluded. In contrast to previous studies, we neither controlled maternal diet and activity nor measured maternal blood hormone and heart rate as all mothers were monitored in the home environment.

Conclusion

Based on clinically unremarkable, but statistically significant differences in the FHR parameters between the AGA and SGA group we suggest that further studies with large sample size are required to assess the clinical value of antenatal fetal ECG monitoring.