The emergence of fetal behaviour. III. Individual differences and consistencies

Abstract

Intra- and inter-fetal consistencies and differences in motor activity were studied in 12 healthy nulliparous women during the first half of gestation. Real time ultrasound observations, lasting 60 min, were performed weekly from 7 to 15 weeks of gestation and at 17 and 19 weeks. The various types of movements were categorized according to a previously developed classification system. Data on general movements during the second half of gestation were carried out on the same group of women and these results are also included in this study. Intra-individually there appeared to be a relative week-to-week consistency in the amount of total motor activity, i.e. the sum of all the movement patterns. There was a slight tendency of intra-fetal consistency when the incidence of general movements during the first half of gestation was compared to that during the second half. The other movement patterns did not show these consistencies, namely, each fetus showed large fluctuations in the week-to-week incidences. Inter-individually there were large differences in the amount of the different types of movements at the various ages, which resulted in wide ranges. The sum of the rank orders which for total activity and general movements, were found weekly, were compared to those which could be expected to occur in a homogeneous population. Two fetuses appeared to be significantly different from the others on mathematical grounds. One consistently showed a high and one a low motor output. Week-to-week stability in the rank orders of the various movement patterns was studied by adding up a sum score of all the weekly changes in ranks. Three fetuses were found to be stable and three showed large fluctuations. The others were in between these extremes. The ranks of the individual movement patterns have emerged they hardly change in appearance in the course of pregnancy (and in the early neonatal period). Adequate knowledge of the distinct movement patterns and observations of sufficient duration might prevent inappropriate interpretation of the movement repertoire. A gradual decline in the incidence of general movements was found during the second half of pregnancy. This is in contrast to the observations of others, who found a mean percentage of 9–18% [14,19] of the recording time during the second half of pregnancy. This incidence was found in this study between 12 and 19 weeks. The difference might be due to the different methods of sampling or to differences in the definition of general movements (“trunk movements”, “gross body movements”). In this study it was only possible to see with one transducer the fetal head, at least one extremity, the thorax and the upper part of the abdomen during the second half of pregnancy. Patrick et al., however, concentrated on the chest and abdomen [14], whereas Roberts et al. observed a transverse section of the abdomen [19]. It may well be that a certain number of movements were missed in this study. On the other hand only general movements were included. Other types of movements such as startles, retroflexion of the head, yawns and stretches, which may cause movement of the trunk were, therefore, excluded.