estimation of gestational age using ultrasound scan

introduction: accurate estimation of gestational age (ga) early in pregnancy is necessary for obstetric care decisions and for determining fetal growth and other conditions that may need intervention or delivery. this study was aimed to compare m enstrual versus ultrasound scan-based gestational age estimates of ga in kermanshsh during 2004-2005. materials and methods: a diagnostic study was done on 15 to 40 weeks pregnant women with reliable and regular menstrual period who referred to motazedi hospital of kermanshah. at first ga history based on last menstrual period (lmp) was recorded by a radiologist.  then another radiologist estimated ga based on transverse cerebella diameter (tcd), biparietal diameter (pd) and femur length using ultrasound scan. the data were analyzed using descriptive and analytical statistics. results: the results showed that mothers age were between 17 to 40 years old.  48.7%of subjects were primi-gravida and 7.5% were five and over m ulti-gravida . ga results were 29.11 5.4, 28.93 5.3, 29.31 5.4 and 29.38 5.4 weeks based on tcd, bd, fl and lmp measurements respectively. the sensitivity of fl was more than other methods (86.9%) and kappa coefficient agreement was 0.976. conclusion: this study confirmed that using femur length method in clinical ultrasound scan has more sensitivity and it is better to use for estimating ga.  further study of standardization of femur length in iranian fetus is highly recommended.