[Comparison between clinical and ultrasonographic measurements to estimate fetal weight during labor: a new clinical calculation formula].

Background: Fetal weight estimation is an important parameter in decision making during labor to avoid delivery complications.

Objectives: To evaluate the reliability of clinical and ultrasonographic measurements in fetal weight estimation during active delivery, as well as to define which is the best method for calculate it.

Material And Methods: Study of 115 healthy pregnant women during labor. Uterine fundus height, uterus wide and adipose panicle thickness, if it were so, were obtained. Fetal weight was calculated by means of Johnson's formula and a new one proposed (Carranza's formula). Also ultrasonographic estimation was done according to Hadlock 1. At birth, newborn's weight was documented and three groups were created according to newborn weight: < 2,500 g, 2,500 to 3,500 g and > 3,500 g. Differences among methods and real weight real were calculated by Student t test, and correlation between methods by Pearson's correlation analysis.

Results: There was a difference between real weight and Johnson's estimation (-104.8 +/- 289.4 g), Carranza's formula (+124.7 +/- 304.7 g), and ultrasonography (-102.0 +/- 299.6 g). Correlation between Carranza's and Johnson's formula was r = 0.796, between Carranza's formula and ultrasonography, r = 0.765, and between Johnson's formula and ultrasonography: r = 0.729 (p < 0.001). Carranza's formula has the lower variation regarding real weight.

Conclusions: Clinical methods as well as ultrasonography were reliable methods to predict fetal weight with the advantage that clinical methods are more economic.