The relationship between birthweight, 25-hydroxyvitamin D concentrations and bone mineral status in neonates

Calcium (Ca), phosphorus (P) and 25-hydroxyvitamin D (25-OHD) are the major micronutrients for fetal skeletal development.

To compare whole body bone mineral density (WB BMD) and bone mineral content (WB BMC) in different birthweights of term neonates and to determine correlations of biological criteria of bone health between neonates and their mothers.

Serum Ca, P, alkaline phosphatase (ALP) and 25-OHD levels were measured in 30 small-for-gestational-age (SGA, group 1), 40 appropriate-for-gestational-age (AGA, group 2) and 30 large-for-gestational-age (LGA, group 3) neonates and their mothers in winter. WB BMD and WB BMC of neonates were estimated by dual-energy X-ray absorptiometry (DEXA) in the 1st 24 hrs after delivery.

Mean (SD) serum 25-OHD levels in the mothers [8.7 (3.0), 8.6 (3.0) and 7.7 (2.8) microg/L, respectively] and their infants [6.3 (2.5), 6.0 (2.2) and 5.7 (1.8) microg/L, respectively] in groups 1, 2 and 3 were similar. Compared with the mothers, the mean 25-OHD levels of the neonates in all groups were significantly lower (p<0.05), and they were highly correlated (r=0.755, p<0.05). Ninety-three per cent of the neonates and 82% of their mothers had 25-OHD levels <10 microg/L, the lowest limit of normal. Mean (SD) WB BMD and WB BMC were higher in LGA infants [0.442 (0.025) g/cm(2), 71.6 (9.0) g, p<0.01, p<0.001, respectively] but lower in SGA [0.381 (0.027) g/cm(2), 29.1 (9.1) g, p<0.001, p<0.001, respectively] than in AGA infants [0.426 (0.022) g/cm(2), 53.7 (9.6) g, respectively]. The percentage of WB BMC was lower in SGA than in AGA and LGA infants. WB BMC and WB BMD were positively correlated with birthweight (r=0.910, p<0.05) and gestational age (r=0.707, p<0.05) but not with serum 25-OHD.

The neonates' bone indices increased significantly with gestational age and birthweight but this was not related to serum 25-OHD levels in the infants and their mothers.