Neonatal Acid-Base Status in Term Fetuses: Mathematical Models Investigating Cerebroplacental Ratio and Birth Weight.

ABSTRACT

OBJECTIVE: Cerebroplacental ratio (CPR) is emerging as a marker of fetal hypoxia at term. The aim of this study was to demonstrate graphically the interrelationships among CPR, birthweight (BW), and neonatal pH, and construct 2D and 3D representations of the areas with potential low pH. METHODS: This was a retrospective study of 2,927 term fetuses evaluated according to BW and CPR. The outcome was the acid-base status at birth. Multivariate relationships among CPR, BW, and arterial and venous pH were depicted in 3D scattergrams. Subsequently, trend surfaces were calculated and represented in 2D contour graphs. Finally, 3D representations were constructed by smothering pH data using moving average filters. RESULTS: The trend surfaces and the 2D and 3D contour graphs showed the complex association among the three variables. Although pH changed with CPR and BW, the influence of the BW was smaller than the influence of the CPR, with this effect being more evident in the venous than in the arterial pH. CONCLUSIONS: Two scenarios threaten fetal well-being at term a very low birth weight and a very low fetal CPR. Our findings suggest that the importance of fetal hemodynamics in determining the acid-base status at birth surpasses that of fetal weight.