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.
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