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

Objective. To assess the relationship between gestational age and sonographic 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 pregnancies from 19 weeks of gestation until term, using transabdominal high-resolution ultrasound techniques. The sternal length, as well as the number of ossification centers at each gestational age, were recorded. Results. The first occasion at which a fetal human sternum could be visualized 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% confidence 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 gestational 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 sternum which may be helpful in the prenatal diagnosis of congenital syndromes that include, among other manifestations, abnormalities of sternal development.