569 LOW FIRST-TRIMESTER PAPP-A IDENTIFIES PREGNANCIES REQUIRING IUGR SCREENING LAURA GOETZL, DAVID KRANTZ, FOR THE NICHD BUN STUDY GROUP, Baylor College of Medicine, Obstetrics & Gynecology, Houston, TX NTD Laboratories, Huntington Station, NY OBJECTIVE: We calculated risk of intrauterine growth restriction (IUGR) after abnormal serum analytes and nuchal translucency (NT) using data from an NICHD multicenter cohort recruited to study Down syndrome detection. STUDY DESIGN: The original study subjects underwent first-trimester screening via PAPP-A, free bhCG, and NT between 10 and 14 weeks’ gestation. Excluded were those with unknown birthweight, significant vaginal bleeding, or current pregnancies with structural or chromosomal abnormalities. IUGR was defined as birthweight 95th and 99th %iles) were compared to women with normal values (5th-95th %ile). Logistic regression allowed us to control for independent variables predictive of outcome. RESULTS: The final cohort, consisting of 6310 live births, showed low levels of PAPP-A or free bhCG to be associated with an elevated risk of IUGR when adjusted for maternal age, weight, race, and smoking (Table). Presence of low analyte (PAPP-A < 5th or free bhCG < 1st %ile) identified 11% of IUGR in our cohort over a baseline risk of 6.2%, with a screen positive rate of 5.2%. PAPP-A < 0.29MoM identified a subset at high risk for IUGRwith a screen positive rate of only 0.9%. Elevated PAPP-A or free bhCG was not associated with IUGR risk. CONCLUSION: Abnormal first-trimester analytes predict only a fraction of later IUGR cases, but PAPP-A < 0.29 MoM identifies a subset of patients with a more than 5-fold increased risk of IUGR. These patients should receive sonographic evaluation of growth after 28 weeks. 570