Summary: In this study 3 different methods of screening for birth-weight <10th percentile in pregnancy were evaluated both indivually and in combination; 1,135 women with singleton pregnancies were studied. Measurements of symphysiofundal height by tape measure, and amniotic fluid index and fetal abdominal circumference by ultrasound imaging, were made at 18, 24, 28, 34 and 38 weeks. At none of these gestational ages did amniotic fluid index perform well as a screening test for birth-weight <10th percentile. Combining the tests, using symphysiofundal height to select a group at high risk who then had a fetal abdominal circumference measurement, reduced the false positive rate but significantly decreased the percentage of infants diagnosed. The results of this study confirm that the most appropriate antenatal diagnostic test for birth-weight < 10th percentile is ultrasound measurement of fetal abdominal circumference. Selecting pregnancies at risk by clinical measurement of symphysiofundal height will provide a lower false positive rate than a policy of performing ultrasound on all pregnancies during the third trimester, but will also reduce the sensitivity.