Our objective was to investigate the longitudinal development of incidence parameters of fetal body movements to define normal reference ranges, to relate them to episodes of fetal heart rate patterns A and B, and to determine the intrafetal consistency for these parameters. Twenty-nine fetuses were studied longitudinally from 24 wk of gestation. Fetal body movements and heart rate were recorded at fortnightly intervals between 24 and 36 wk of gestation and weekly from 36 wk of gestation. Data were analyzed using multilevel analysis. Reference ranges were constructed for the percentage of observation time that movements were present, the number of movement bursts per hour, the mean burst duration, and the median onset-onset interval. The median percentage incidence of fetal body movements decreased from 17% at 24 wk to about 7% near term. The developmental course was the same during active episodes. Body movements also decreased during episodes of relative quiescence, in the course of pregnancy. Intrafetal variance was on average 40 -80% of the total range of the four movement parameters. Normal reference ranges were developed for incidence parameters of fetal body movements from 24 wk of gestation onward. The overall decline in the incidence of movements during pregnancy appeared to be a developmental phenomenon and not due to progressively increasing episodes of fetal quiescence. Individual fetuses showed a degree of consistency in the percentage incidence of body movements, but intra-and interfetal variances were generally high, resulting in wide ranges. (Pediatr Res 52: 568-575, 2002) Abbreviations FHR, fetal heart rate FHRP, fetal heart rate patternThe majority of neurodevelopmental disabilities have been estimated to originate from prenatal factors (1). Both the quantity and quality of fetal body movements have been recognized as important indicators of fetal well being and of the integrity of the CNS (2, 3). Studying fetal body movements could therefore provide a key to elucidate the prenatal etiology and pathogenesis of abnormal neuromotor development, which might, eventually, facilitate early intervention and optimal treatment before, during, and after birth. There is evidence that the quality of fetal body movements is more likely an indicator of brain integrity than the quantity of movements (4, 5). However, before either of the two can be used as such in clinical practice, the normal developmental course and its possible sources of variation must be defined. This requires the use of a prospective longitudinal study design (6). In the present study, we focused on the developmental course of various quantitative aspects of fetal body movements.Several authors have reported on the incidence of fetal body movements. However, because of the absence of a uniform definition of a body movement, and differences in study design (longitudinal or cross-sectional) and data analysis, the reported mean/median values and ranges of normality differ greatly among the various studies (7-16), as we have recently describ...
