[Johnson and Toshach method utility for calculating fetal weight in term pregnancies within a second level hospital]

To evaluate the utility of the Johnson and Toshach's method to calculate the fetal weight before the birth in patients with term pregnancy.

A longitudinal, transversal and prospective study was done to analyze 244 patients between 37 to 41.6 weeks pregnancy, they were physically examinated and questionated, the body mass index was calculated and Johnson & Toshach method was used to calculate the fetal weight. The calculated weights with the formula were compared with the fetal weights measured at birth with t-Student's test to determine if significative difference exists (p < 0.05) between the medias of both groups. The data were classified in five categories according to the gestational age and the weights were compared using the Tukey's test to compare the statistic medias (p < 0.05).

The category of the 39 to 39.9 gestational weeks of the study group is accounted for 29.5%, the calculated weight's media with the Johnson & Toshach method was of 3,292.88 g while the media of the real weights was of 3,273.13 g. There wasn not significative statistic difference between both groups with a variation of +/- 126 g. There is a correlation of 0.940 between the calculated weight and the real weight. The media of the weights calculated in the macrosomic products was of 4,252.5 g, and the media of the real weights was of 4,293.86 g, there is not significant statistic difference (p = 0.59). According to the gestational age, there was not significant difference. The 9.01% of the cases is represented by the macrosomic products (22) whose were obese in 77%.

The Johnson and Toshach method is useful with a 95% confiability because there was not significant difference between the fetal weight measured and the weigth estimated by the formula, it is a non invasive method, of easy application that permits to detect fetal macrosomia with a variation of +/- 126 g (limit of variation stablished in the original technique is of +/- 240 g). We consider that the formula is useful to detect macrosomic products.