Normal values of aortic root measurements in neonates.

Aortic root diameter measurements were obtained during the first week of life by M-mode echocardiography using leading edge methodology during early diastole in 172 preterm and 228 term neonates. At least 40 newborns were included in each 500-g birth-weight subgroup from 750 to 4750 g. The aortic root diameter increased linearly from 0.63 +/- 0.04 cm in newborns with birth weights of 750-1249 g to 1.06 +/- 0.06 cm in newborns of 4250-4750 g.