Calcification of the lumbar vertebrae during human fetal development.

The calcification rate of the human fetal vertebrae has not been previously documented. In bridging this gap in knowledge, this report will specifically provide reference values for mineral content in predominantly trabecular bone during its formation in the prenatal period. Such information would facilitate early detection of ossification defects which become apparent in the fetal spine as early as 20 weeks of gestation [1]. Lumbar vertebrae were obtained at autopsy from 33 human fetuses aged 17-41 weeks of gestation. Vertebral demineralization was effected using an acid-alcohol solution. The extracted concentrations of calcium and phosphorus were determined spectrometrically from the solutions. Atomic absorption spectroscopy was used to determine calcium concentration and phosphate concentration was assessed by ultraviolet colorimetry. Mineralization could be described by a linear relationship over the age range studied. Calcium was taken up by the fetal vertebrae at twice the rate of phosphorus (0.2% per week). When the fetuses were classed according to similar gestational ages, the Ca/P weight ratios increased from 1.7 in the youngest group to 2.2 in the oldest group. The time of onset of calcification, calculated by extrapolation of the calcium data, appeared to be earlier than ultrastructural studies by other investigators suggest, but was subject to many uncertainties.