An interpretation of the neonatal period definition obtained with echocardiographic examination by using change point regression analysis.

BACKGROUND: We had reported on the left ventricular end-diastolic dimension (LVDd) in normal children from the premature/neonatal period to the adolescence period by using two-dimensional echocardiography, and formulated equations to evaluate normal LVDd values by using body height as an index. There was an inflection point at around birth that seemed relevant to the fetal and neonatal periods for the relation of LVDd and body height.

METHODS: We aimed to reveal the true inflection point and its meaning by using change point regression analysis. The study group consisted of 421 neonates and infants. The ages at examination ranged from 24 weeks' gestation to 1 year after birth. The subjects' body heights at examination were between 31 and 75 cm.

RESULTS: The analysis showed no definite inflection point in height, and a flat bottom was observed between body heights of 48 and 55 cm. The inflection range seemed to mean the duration of the neonatal period, which connects the fetal and infantile periods.

CONCLUSION: The results revealed that neonates reach the infantile period slower than usually imagined, and the end of the neonatal period may be at the age when the body height is around 55 cm- in other words, at 2 months after birth. This manuscript might be the first one to consider the definition of the neonatal period using cardiovascular methods.