Based upon 2194 consecutive pregnancies with known gestational age, formulas for weight deviation predicted in the 32nd and 37th gestational week were estimated by multiple linear regression on the measurements of the abdominal diameter (AD) and the biparietal diameter (BPD) of the first 64% of the pregnancies. The usefulness of the screening was evaluated on the remaining 36%. An attempt to diagnose light for gestational age (LGA) infants resulted in either a low sensitivity or a low predictive value of a positive test. The late third trimester screening was more sensitive than the early, indicating LGA as a late phenomenon in pregnancy. Knowing the result from the late scanning, the result from the early scanning contributed almost no further information about whether the infant would be LGA at birth. Basic epidemiological characteristics of other comparable investigations on high-risk pregnancies and non selected pregnancies are presented.