Correlation between regular mouthing movements and heart rate patterns during non-rapid eye movement periods in normal human fetuses between 32 and 40 weeks of gestation

Abstract

Background: Regular mouthing movements (RMMs) are observed during fetal non-rapid eye movement (NREM) periods.

Aim: To determine the correlation between RMM and fetal heart rate (FHR) patterns during NREM periods.

Study design: Fetal eye and mouth movements and FHR patterns were observed and recorded.

Subjects: 50 normal singleton pregnancies between 32 and 40 weeks of gestation.

Outcome measures: Changes in the power spectrum ratio of 3-minute blocks of RMM clusters, FHR with RMM clusters (HR+), and FHR without RMM clusters (HR-) were calculated at a frequency band of 0.02 Hz among 3 gestational age groups: group 1, 32-34 weeks gestation; group 2, 35-37 weeks gestation; group 3, 38-40 weeks gestation. We calculated the percentage of cases showing dominant peak ratios of RMM and HR+ in the same frequency band, the maximum correlation coefficient, and its lag time.

Results: In group 3, the dominant peaks of both RM and HR+ were present at the same frequency band, 0.06-0.08 Hz; this was not seen in the other groups' relative power spectral patterns. The percentage of cases showing dominant peaks of RMM and HR+ in the same frequency band increased with advancing gestational age. The maximum correlation coefficient in groups 1 (0.28 ± 0.11) and 3 (0.45 ± 0.14) differed significantly (p<0.05).

Conclusions: The correlation between RMM and FHR patterns became stronger, and their rhythmicity was similar, from 38 to 40 gestational weeks, suggesting that a common center starts to govern both patterns at approximately 38 weeks gestation.