The development of the fetal sternum: a cross-sectional sonographic study

Objective To assess the relationship between gestational age and sonographi c appearance of the various sternal components and establish growth during human gestation. Design A prospective cross-sectional study. Methods The study was performed on 252 consecutive normal singleton pregnan cies from 19 weeks of gestation until term, using transabdominal high-resol ution ultrasound techniques. The sternal length, as well as the number of o ssification centers at each gestational age, were recorded. Results The first occasion at which a fetal human sternum could be visualiz ed with two to three ossification centers was at 19 weeks' gestational age. The fifth ossification center was first visualized at 29 weeks' gestation. The mean +/- SE of sternal length varied from 15 +/- 0.98 mm (95% confiden ce interval (CI) 12.79-17.21) at 19-20 weeks, to 36.50 +/- 0.29 mm (95% CI 35.58-37.42) at 37-38 weeks' gestation. Sternal length as a function of ges tational age was expressed by the regression equation: sternal length (mm) = -11.06 + 1.39 x gestational age (weeks). The correlation coefficient, r = 0.924 for sternal length, was found to be highly statistically significant (p < 0.0001). Conclusions The presented data offer normative measurements of the fetal st ernum which may be helpful in the prenatal diagnosis of congenital syndrome s that include, among other manifestations, abnormalities of sternal develo pment.