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Comparative Study of Four Methods of Clinical Estimation of Fetal Weight in the Late Third Trimester Admitted for Delivery: A Prospective Study

Ma. Rosielyn D. Asto, MD; Ma. Cristina P. Crisologo, MD, FPOGS, FPSMFM
Department of Obstetrics and Gynecology, Philippine General Hospital-University of the Philippines-Manila

Background: Clinical estimation of fetal weight is a basic skill an obstetrician should master. Although the use of ultrasound has gained much popularity in the recent decade, in low resource settings, most patients do not have the luxury to have an ultrasound done for their babies, more so a sonographic estimate. Four methods of clinical estimation – Dare’s method, Johnson’s formula, Modified Johnson’s Formula and abdominal palpation were used in the study and compared with the actual weight of the baby.

Objective: To come up with the best/most reliable clinical method to use in estimating fetal weight among women in the late third trimester of pregnancy.

Methodology: The study used a prospective study design. All women beyond 34 weeks age of gestation admitted at the OB admitting section and ward were included. A total of 370 parturients were included. Senior residents on duty at the OB admitting section were asked to record their examination after the patient had given her consent. Those admitted at the wards were examined by the resident in charge and principal investigator after the patient consented to the study. The actual birthweight was used as the gold standard value. Paired Sample T-test was used to determine whether the estimates are comparable to the actual birthweight. Each formulae for estimating fetal weight were compared to the actual birthweight. Percentage error of each was computed and compared using the Wilcoxon Test and absolute percentage error were compared using T-test. One-way ANOVA test was used to determine inter-observer difference.

Results: The palpation method had the lowest mean absolute error, followed by Dare’s Method. The Modified Johnson’s Formula had the highest mean absolute error. Similarly, the palpation method had the highest number of estimates with difference less than 100 grams from the actual value. This is consistent with the absolute percent error which showed that the palpation method has most estimates (73.2%) having less than 5% error, followed by Dare’s Method (49.5%), and Johnson’s (38.6%). The Modified Johnson’s Formula had the least number of estimates at less than 5%, at 10.8%. At 34 – 37 weeks age of gestation, the palpation method had the lowest mean percentage error (0.41±5.18) followed by Modified Johnson’s formula (1.40±15.54). The Johnson’s Formula yielded the highest percentage error at 13.29±18.56. At 37 weeks age of gestation and above, the Dare’s Method had the lowest mean percentage error (0.91±8.51), followed by the Johnson’s Formula (-1.14±9.62), then Palpation Method (-1.59±6.16).

Conclusion: Based on the data garnered, the clinician’s estimate using the palpation method is by far the most accurate in any age of gestation, followed by Johnson’s Method, with the Modified Johnson’s Method with the least accurate estimate. At 34-37 weeks age of gestation, the palpation method had the closest estimate. At 37 weeks age of gestation and above, the Dare’s Method is more superior.

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