Baseline Diameters of Inferior Vena Cava and Abdominal Aorta Measured by Ultrasonography in Healthy Term Neonates During Early Neonatal Adaptation Period

Abstract

Objectives: To evaluate normative sonographic measurements of the inferior vena cava (IVC), aorta (Ao), and IVC/Ao ratio in the first 2 days of life in term neonates.

Methods: We prospectively observed 200 term (more than 36 and 6/7 weeks of gestation), single, healthy neonates born in a city hospital. The exclusion criteria were congenital abnormalities, an Apgar score of less than 8, and hyperbilirubinemia requiring phototherapy. Maximum IVC (distal to the hepatic-IVC junction) and Ao (above the superior mesenteric artery) diameters were measured in the first 2 days of life in the longitudinal plane. Neonatal weight loss was calculated as a percentage lost from birth weight (BW).

Results: A total of 200 (50% born vaginally, 53% male) neonates were enrolled. Correlations between IVC and aortic diameters as a function of gestational age, method of birth, weight loss, and body surface area (BSA) were calculated using the Spearman's rank correlation coefficient. The correlation coefficients were statistically significant for the IVC (P = .017) and Ao (P = .006) abdominal diameters versus gestational age. The Ao diameter correlated with BSA (P = .0001). In neonates with weight loss less than 8% of BW, the IVC/Ao ratio remained constant at 0.62 (95% confidence interval, 0.60-0.63).

Conclusions: Sonographic measurements of IVC and Ao maximum diameters in term neonates suggests a significant positive correlation among gestational age, BSA, and IVC and Ao diameters. The IVC/Ao ratios remain constant over 48 hours after birth in neonates with weight loss up to 8% of BW, and appear to be lower than previously reported ratios for healthy children.

Keywords: IVC; IVC/Ao ratio; abdominal; aorta; inferior vena cava; neonatal adaptation period; pediatrics; term neonate.