The relationship between estimated weight of the fetus using two ultrasound and Johnson methods with actual weight of the baby at birth in pregnant diabetic mothers

Fetal birth weight, as one of the most important indicators for evaluating the health of newborns, is influenced by various factors such as maternal diabetes. Fetal weight estimating is necessary for planning the type and time of delivery. The present study was performed with aim to compare the estimated fetal weight before birth with the actual weight of the baby after birth in diabetic mothers.

This descriptive-cross-sectional study was done from April 2022 to April 2023 on 71 diabetic mothers in the obstetrics and gynecology department of Imam Reza and Qaem hospitals in Mashhad. All the characteristics of the mother were recorded in the researcher-made checklist. The fetal weight before termination of pregnancy was estimated by ultrasound and also by Johnson's clinical formula, and then the actual weight of the baby was measured after delivery. Data were analyzed by SPSS software (version 22). To compare the fetal estimated weight with the actual weight after birth, Pearson's test was used to evaluate the type of correlation (p<0.001) and Bland Altman's diagram was used to check the pattern of agreement.

In the Pearson correlation analysis, there was a positive and statistically significant correlation between the estimated weight by Johnson's method and ultrasound with the actual fetal birth weight, and in the presence of different variables, this correlation was still positive and significant (r=0.9, p<0.001). In the investigation of any agreement pattern between different methods of fetal weight estimation using Bland Altman method, which was based on the distance between the upper and lower limit of agreement between different methods, it was shown that this distance between Johnson's estimated fetal weight and the actual fetal weight was 1230.44 gr, between the Ultrasound and real weight was 1111.84 gr and between ultrasound and Johnson was 1136.8 gr, which did not have an acceptable level of agreement.

Despite the positive and significant correlation between Johnson's clinical fetal weight estimation and ultrasound, these methods cannot be replaced for each other in estimating the fetal weight, and considering the reported difference, ultrasound estimated fetal weight compared to Johnson's method is closer to actual fetal weight.