Clinical estimation of fetal weight in low resource settings: comparison of Johnson's formula and the palpation...

Estimation of fetal weight is important for antenatal and intrapartum clinical decision-making. Sonographic estimates may not always be available in low resource settings. In such instances it is essential to study the reliability of clinical estimation of fetal weight in assisting decision-making.

Estimate the accuracy of the Johnson's formula and the palpation methods of fetal weight estimation and their correlation.

Maternity units of three teaching hospitals (Tikur Anbessa, Gandhi Memorial and Saint Paul's) in Addis Ababa, Ethiopia.

Three hundred and twenty mothers were included in the study at the three hospitals from May 1 to September 30, 2004. Fetal weight was estimated for each mother using both methods prior to delivery. Accuracy of estimation was determined by the percentage error, absolute percentage error and the proportion of estimates within 10% of the actual birth weight. Statistical analysis was performed using the student's t test, paired t test, comparison of correlated variances using the modified F test, Wilcoxon sign test and the X2 test.

Actual birth weight was 3152 +/- 494 grams; ranging from 1600-5250. The mean of all error terms of EFW (estimated fetal weight) with palpation method were significantly smaller than those of Johnson's method and rate of estimates within 10% of actual birth weight was significantly higher for the palpation method (65%, versus 38%). For birth weights less than 2500 grams both methods overestimated the birth weight; the mean error of the palpation method was significantly smaller than those of the Johnson's method. In the 2500-3999 birth weight range, only the palpation method had no systematic error, whereas the Johnson's method systematically overestimated the birth weight. The mean errors of the palpation method were significantly smaller and a rate of birth weight +/- 10% significantly higher than those of the Johnson's method (68% versus 40%). In the larger weight (>4000 gms), the Johnson's method had less systematic error compared to the palpation method (mean percent error = -0.9 + 11.3. p =0.42), although the small sample size in this group precludes a firm conclusion of the issue in this category.

Estimation of fetal weight by the Palpation method appears to be more accurate than the Johnson's method. In the lower and average birth weight range the palpation method is the more accurate of the two, while in the higher weight category the Johnson's method appears to be more accurate.