ABSTRACT
Estimation of the gestational age [G.A] and the estimated date of confinement [EDC] are of paramount important factors in prenatal care units. Naegle's rule is a usual method for determining GA and EDC based on the LMP in which 7 days added and 3 months subtracted. Nowadays sonography is one of the routine methods for estimating date of delivery and gestational age. The aim of this study was to determine the accuracy of Naegele's rule and sonography for estimating of delivery date. In this analytic-descriptive study, a total of 260 pregnant women from the Yazd prenatal care clinic were equally divided into second and third trimester. The EDCs of these ladies were determined by Naegele's rule and sonographic BPD and FL measurement. The values of these two methods were then compared with actual onset of the spontaneous labor. The difference between EDC based on the Naegele's rule and actual onset of labor was [-5] - [+8] days. However, this value changed to [-1] - [+18] when performed sonography was based on EDC. The derived means were 2.21 days for the Naegele's rule and 4.32 days for sonography at the second trimester, and at the third trimester, these figures were 2.42 days and 9.20 days respectively. The results suggest that the Naegele's rule is more accurate than sonography for the determination of EDC, and these methods especially sonography become less accurate with increasing gestational age