[Sensitivity and predictive value of the Johnson and Toshach method to estimate fetal weight]

Several clinical methods have been used to follow up fetal growth, mainly based in uterine enlargement. Ultrasound (US) is nowadays the main tool to evaluate fetal growth; however, is not widely available. Thus, we decided to evaluate the Johnson and Toshach method (JTM) to predict newborns weight on clinical basis.

to evaluate the sensitivity and positive predictive value of the JTM. We selected 132 women with single term pregnancies whose gestational age was previously confirmed by US, and followed the method described by JTM. At the end of pregnancies by delivery or cesarean section, we compared our estimations with the newborn infant's weight. In order to avoid bias, only women whose pregnancies ended in the following 72 hours were included. All clinical measurements were done by one observer. The sensitivity, specificity and positive predictive value of the JTM were calculated.

We found non-significant difference between the mean of the fetal weight (3,295 g) calculated with the JTM and the mean of the newborn infants weight (3,343 g) (p = NS). The standard deviation was 325 g and the standard error mean was >or=53 g or 16 g/kg (error = 1.6%). In normal weight groups of neonates, the JTM had a sensitivity of 97%, a specificity of 71% and the positive predictive value was 98%. We observed a higher sensitivity in the detection of macrosomy (80%) than of low-weight newborns (33%), but with an inverted specificity of 71.4% vs. 99.2%, respectively.

The JTM is a useful clinical technique to estimate fetal weight in the third trimester of gestation that may be applied when US is not available, being more sensitive to detect normal weight than macrosomic or low-weight newborns.