Radiological evaluation of bone growth in neonates born at gestational ages between 26 and 41 weeks: cross-sectional study.

The length of the ossified part of the long bones of the upper (humerus) and lower limb (femur) as well as the axial length (that is, height) of the vertebral body of L1 were measured on a plain supine radiograph in 347 newborn babies (228 males, 119 females) with the gestational age (GA) from 26 to 41 weeks. All were admitted to the neonatal intensive care unit. Reasons for admission included hyaline membrane disease, meconium aspiration syndrome, neonatal asphyxia or transient tachypnea of the newborn. Patients with abnormal growth, gross anomalies, or who were the products of multiple births were excluded. The average weekly increment in the height of L1 for male infants born at GA varying from 26 to 41 weeks was 0.23 mm, for the humerus 1.82 mm and for the femur 2.35 mm. The corresponding data for females was 0.20 mm, 1.54 mm and 2.30 mm. The ratio of the height of L1 to body length progressively increased between 26 to 41 weeks. A growth spurt in L1 was noted for both sexes at 34 weeks of GA. Long bone growth was similar in male and female infants born before 36 weeks. However, the ratio of femur to body length in males increased after 36 weeks. The ratio of humerus to body length remained constant over the entire range of GA.