[An allometric study of the relative growth of the head and the body of the fetus and of the new born (author's transl)].

An allometric study of the relative growth of the head and the body of the fetus and of the newborn shows that there is a more rapid growth of the head in relationship to the length of the fetus before the 30th week of pregnancy and then there is a slowing down between the 30th and the 40th weeks, followed by a re-acceleration after birth for full term infants. This phenomenon is not shown in premature babies born before the 30th week of pregnancy who continue their head growth with the same speed after birth and slow down only for a short time near their theoretical term. These results led to a hypothesis being formed that cephalic growth is slowed down in the uterus because of steric (molecular) congestion, a slow-down that is slightly demonstrated in breech presentations and much later in very premature babies. This opens the way to a discussion on the final results of this phenomenon on the brain.