PRENATAL DEVELOPMENT OF ARM POSTURE

Fetal arm posture was studied longitudinally in 10 uncomplicated pregn ancies using real-time ultrasound. Observations were performed at four weekly intervals from 12 to 36 weeks, and at 38 weeks. The percentage of assessments with optimal visualization of elbow, wrist and fingers was 84% at 12 weeks and more than 90% thereafter (range 92-98%). Ther e was a clear developmental trend towards increased flexion. Flexion o f the elbow occurred frequently from 12 weeks onwards with an increase d incidence at 16 weeks, that in the fingers from 20 weeks onwards and from 28 weeks to term age in the wrist. All three trends were statist ically significant. There was considerable intra-individual consistenc y in terms of the ages at which flexion increased. In fact the increas e of flexion occurred one session later in only 6/30 registrations. Th e combined data of the elbow, wrist and fingers revealed preferential arm posture at 12 weeks with the elbow flexed and the wrist and finger s extended. From 16 to 28 weeks, the predominant posture consisted of elbow flexion, wrist extension and finger flexion and complete flexion thereafter. The development of fetal arm posture does not comply with a proximo-distal trend in that there was first an increase in flexion at the elbow, followed by the fingers and finally the wrist. The impl ications of our findings for understanding the prenatal development of the central nervous system and subsequent postural adjustments to ext rauterine life are discussed. (C) 1998 Elsevier Science Ireland Ltd.