Summary: One of the most important objectives of ultrasonographic fetal biometry is the accurate gestational age (GA) estimation. The crown – rump length greater than 10mm has the best correlation with GA at 8–12 gestational weeks. GA could be estimated at 5–7 gestational weeks, measuring the dimensions of the gestational sack. Biparietal diameter is the main parameter that can me measured in the second trimester for GA estimation, but fetal head circumference can be used as well applying the “ellipse” function. However, when fetal head appears to be dolichocephalic or brachicephalic, femur length could be additionally used for GA estimation. At the third trimester of pregnancy, GA estimation could be improved when measuring the length of fetal kidneys. The main failures of GA estimation occur due to the application of fetal abdominal parameters or rather out of date and adjusted for an inappropriate population standards. Key words: gestational age, ultrasonographic fetal biometry.