Bone mineral deficiency as the main factor of dolichocephalic head flattening in very-low-birth-weight infants.

We hypothesized that the postnatally reduced rate of bone mineralization observed in many very-low-birth-weight (VLBW) infants is the main cause of dolichocephalic flattening of the head in this group of newborns. We measured head shape by using the ratio of the frontooccipital and biparietal diameters, bone mineral content (BMC) at the right midhumerus, birth weight, body weight, and postnatal age at the time of BMC measurement in 85 newborn infants during the first 5 d of life (gestational age: median 34 wk, range 24-40 wk; birth weight: median 1.590 g, range 430-6.730 g) and in 269 VLBW infants at transfer to other hospitals or discharge. The head shape shortly after birth was not influenced by gestational age. Mean frontooccipital diameter/biparietal diameter was 1.27 +/- 0.73 SD (range 1.13-1.59). Stepwise multiple regression analysis from 315 measurements made in 46 VLBW infants during the first 5 d after birth and the 269 infants at discharge revealed a 27% contribution of BMC/body weight to the variation in head shape. The other variables had only a small effect (gestational age 4%, body weight 1%) or no observable effect on head shape. At discharge, the ratio of BMC to body weight was significantly lower than in the reference fetuses of the same body weight. The results support the hypothesis, and we speculate that there is a causal relationship between the head shape of VLBW infants at discharge and the amount of calcium and phosphorus given as a supplement until that time.