Postnatal head shrinkage in small infants.

The front-occipital circumference, frontooccipital and biparietal diameters, degree of suture overriding and weight were measured daily during the first week of life in 50 infants of birth weight under 2,000 gm. In a second similar group of 21 infants, fronto-occipital circumference, weight, and sodium balance were measured daily during the first week of life. Head volumes were estimated from the circumference and diameters of the head. The parameters of head size and derived volumes changed maximally and significantly in the direction of intracranial shrinkage around 3 days of age. The degree of shrinkage was significantly correlated (P less than .005) with the degree of weight and cumulative sodium losses, and decreasing gestational age. We postulate that postnatal head shrinkage results from shift of sodium and water outward from the intracranial cavity as a transient phenomenon during the first week of life. The significance of head shrinkage is discussed.