SCREENING FOR THE SMALL FETUS - A STUDY OF THE RELATIVE EFFICACIES OFULTRASOUND BIOMETRY AND SYMPHYSIOFUNDAL HEIGHT

In this study 3 different methods of screening for birth-weight <10th percentile in pregnancy were evaluated both indivually and in combinat ion; 1,135 women with singleton pregnancies were studied. Measurements of symphysiofundal height by tape measure, and amniotic fluid index a nd fetal abdominal circumference by ultrasound imaging, were made at 1 8, 24, 28, 34 and 38 weeks. At none of these gestational ages did amni otic fluid index perform well as a screening test for birth-weight <10 th percentile. Combining the tests, using symphysiofundal height to se lect a group at high risk who then had a fetal abdominal circumference measurement, reduced the false positive rate but significantly decrea sed the percentage of infants diagnosed. The results of this study con firm that the most appropriate antenatal diagnostic test for birthweig ht <10th percentile is ultrasound measurement of fetal abdominal circu mference. Selecting pregnancies at risk by clinical measurement of sym physiofundal height will provide a lower false positive rate than a po licy of performing ultrasound on all pregnancies during the third trim ester, but will also reduce the sensitivity.