The Study of the Accuracy of Three Methods in Estimation of Delivery Date

Estimation of delivery date based on last menstrual period and ultrasound is common in prenatal care. The aim of this study was to compare the accuracy of Naegel’s rule, Naegel’s revised rule and ultrasound in estimation of delivery date. This cross-sectional study was done on 540 pregnant women hospitalized in Mobayyeni Hospital in Sabzevar (2007-2008) due sign of to labor. Estimated delivery date was calculated based on three methods and difference between these and ture date of labor calculated. Data was analyzed by descriptive statistical indices, Pearson correlation and T-test using Spss15. Results showed that delivery happened in 6.3, 6.3 and 6.7 percent of women just on the stimated date by Naegel’s rule, Naegel’s revised rule and ultrasound respectively and delivery happened in 51.9, 67.2 and 60.7 percent of them until the estimated date. The difference between true date and the estimated date by Naegel’s rule and ultrasound were correlated significantly with fundal height and birth weight (p<0.001). Post term delivery rates were 0.4, 1.9 and 0.6 percent respectively, based on ultrasound reports, Naegel’s rule and Naegel’s revised rule. Naegel’s rule is more accurate in prediction f delivery date, compared to other similar studies. Using ultrasound prolongs the period preceding the beginning of labor. Using Naegel’s revised rule strongly brings better results.