PRENATAL HEAD POSITION FROM 12-38 WEEKS .1. DEVELOPMENTAL ASPECTS

Fetal head position relative to the fetal body was studied longitudina lly in 10 uncomplicated pregnancies by means of real-time ultrasound. Registrations were made at 4 weekly intervals from 12 to 36 weeks, and at 38 weeks. The percentage of assessments with optimal visualization of head position for analysis increased with age. The development of head position involved a change from a midline to a lateralized prefer ence. It was only at 38 weeks that a clear lateralized head position w as found with the head being held mainly to the right, The degree of i ntra- and inter-individual variability was considerable, a finding typ ical of motor behaviour in the healthy fetus. It is hypothesized that this bias is due to neural maturation. The implications of our finding s for the subsequent development of hand preference are discussed.