Abstract
BackgroundPrevious researchers have studied circadian changes in the fetal heart rate (FHR) on small sample sizes and in a strictly controlled environment. This study was undertaken to investigate these changes during the late second and third trimesters, using a portable fetal electrocardiogram recording device (Monica AN24) in pregnant women in home and hospital environments with unrestricted mobility.MethodsThis was a prospective cohort study of 54 pregnant women with uncomplicated singleton pregnancies between 25 and 40 weeks gestation. FHR recordings were made up to 16 h at home or in the hospital setting in the United Kingdom. FHR data over 90 min periods were averaged and the day (7:00 am–11:00 pm) and night (11:00 pm–7:00 am) data from the same individual were compared. Data were examined for evidence of sex-related differences.ResultsDuring the night, there was a significant reduction in basal heart rate (bFHR) and a significant increase in short term variation (STV) and long term variation (LTV) (P < 0.05). Basal FHR decreased (P < 0.002), whereas LTV increased (P = 0.014) with advancing gestation. Male fetuses showed greater day: night variation than females regardless of gestation (P = 0.014). There was a higher bFHR in fetuses monitored during the day in hospital (P = 0.04).ConclusionThis study demonstrates that there are sex-, environment and time-related differences in the FHR parameters measured. These differences may need to be considered taken when interpreting FHR data.
Highlights
Previous researchers have studied circadian changes in the fetal heart rate (FHR) on small sample sizes and in a strictly controlled environment
Regression analysis showed the change in basal fetal heart rate (bFHR) to be strongly reciprocally-associated with Gestational age (GA) at the time of recording (Fig. 1; P < 0.002); the addition of place of recording to the analysis significantly (P < 0.01) improved the final r to 0.554 (P < 0.001)
The change in long term variation (LTV) was directly related to GA (r = 0.331; P = 0.014); there was no effect of GA at recording or place of recording on day: night change in either short term variation (STV) or Root mean square of successive difference (RMSSD) (P > 0.1, >0.3 respectively)
Summary
Previous researchers have studied circadian changes in the fetal heart rate (FHR) on small sample sizes and in a strictly controlled environment. Animal work has confirmed that in the adult information on circadian variation, which is driven by the biological clock located in the suprachiasmatic nuclei of the hypothalamus, is conveyed to the heart via the autonomic nervous system (ANS) [4]. It is less clear whether the fetal suprachiasmatic nucleus plays such a role in the generation of prenatal diurnal patterns, as the Circadian variation in FHR in the human fetus has been reported from as early as 20–22 weeks through to the end of pregnancy [1]. Fetal behavioural state and maturation [8] fetal rest-activity cycles [9] and general body and breathing movements can influence FHR and its variability [10]
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