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A comparison between palpation method and Johnson’s rule to estimate fetal weight in term singleton pregnancies with cephalic presentation in a tertiary hospital: A prospective cross-sectional study

Menabelle A. Marcaban, MD and Ma. Regale Noemi R. Ochoco-Sotto, MD, FPOGS, FPSREI, FPSGE
Department of Obstetrics and Gynecology, Quezon City General Hospital

Background: Estimation of fetal weight through ultrasound or clinically, is important in the management of pregnant women. In low resource settings, where ultrasound is scarce, determination of the superior clinical method between Johnson’s rule and palpation method is of significant value.

Objective: The objective of this study was to determine the best clinical method in estimating fetal weight in term parturients in a tertiary government hospital. 140 term mothers with singleton pregnancies in cephalic presentation were included in this study.

Methodology: Fetal weight was estimated using both palpation method and Johnson’s rule and compared to the actual fetal weight. Effects of body mass index (BMI), cervical dilatation, and engagement on the accuracy of both methods were evaluated using one-way ANOVA and test of proportions. The accuracy of both methods were calculated by mean absolute error and bias. Bland-Altman analysis was used to see limits of agreement and the mean difference between estimated fetal weight to actual birthweight.

Results: Mean estimated fetal weight (EFW) was 2846.39 ± 427.29g by Johnson’s and 2904.29 ± 372.79g by palpation with a mean actual birthweight of 3028.30 ± 441.52g. Using paired t-test, no significant differences were found in EFW by the two methods and actual birthweight. Palpation had more estimates that differed from actual by < 100 grams at 41.43% compared to 16.43% for Johnson’s with p < 0.001. Lower bias (7.11%) was seen in palpation compared to Johnson’s (12.09%) and with more precise estimates.

Conclusion: Palpation method is more accurate and reliable than Johnson’s rule. Clinical palpation is easy, cost effective, simple and should be considered as a diagnostic tool for fetal weight estimation especially in rural areas. The effect modifiers are cervical dilation for palpation and engagement for Johnson’s. BMI has no effect in accuracy of estimates in both methods.