significantly correlated with PT growth (r=0.80). CRL at days 9-10 showed the highest correlation (r=0.74 and r=0.51) while BPD at day 14 had the lowest correlation (r=0.24) with BW. In the multivariate model, CRL at day 9 was the best predictor of BW (F=18.80; p0.05). At day 9, CRL was significantly lower in sFlt-1 mice compared with controls (1.25  0.26 mm vs 1.65  0.32 mm; p0.05). CONCLUSIONS: Mouse CRL in early gestation is a good predictor of BW. Overexpression of sFlt-1 is associated with early fetal growth abnormality, and prior to the previously reported preeclampsia-like findings. Fetal and placental growth can be evaluated longitudinally by microultrasonography, and this approach can be a useful tool to study fetal development in rodent animal models. 353 The influence of maternal obesity on the sonographic evaluation of large for gestational age (LGA) infants? Katherine Goetzinger 1 , Methodius Tuuli 1 , Anthony Odibo 1 , Kimberly A. Roehl 1 , George Macones 1 , Alison Cahill 1 1 Washington University in St. Louis, St. Louis, MO OBJECTIVE: To evaluate the effect of maternal body mass index (BMI) on the performance of ultrasound in the prediction of birthweight in patients referred for the indication of size greater than dates (SD). STUDY DESIGN: This is a retrospective cohort study of 2,562 patients referred for third trimester ultrasound at our institution for the indi- cation of SD. The rate of discordance between estimated fetal weight (EFW) 90th%ile for gestational age (GA) and actual birthweight (BW) 90th%ile for GA was determined for each maternal BMI cat- egory. For patients who underwent ultrasound within 3 weeks prior to delivery, the percent error between EFW and acutal BW was calcu- lated ({EFW-BW/BW}  100) for each BMI category, and mean per- cent error was compared between BMI categories. (BMI 25 = ref- erence) RESULTS: Of 2,562 patients who underwent third trimester ultrasound for the indication of SD, 285 (11.1%) had an EFW 90th%ile for GA on ultrasound, and 680 (26.5%) had an actual BW 90th%ile for GA. The overall rate of discordance between EFW and BW 90th%ile for GA was 23.3%, and the mean percent error was -4.2%. There was no statistically significant difference in mean percent error when com- paring either overweight (BMI 25-30) or obese (BMI30) patients to patients with a BMI25. CONCLUSIONS: In patients referred for the indication of SD, the ac- curacy of ultrasound is not dampened by increasing BMI. Ultrasound continues to be a useful tool in assessment for macrosomia risk in the face of the growing obesity epidemic. BMI EFW>90 th (n285) BW>90 th (n680) Rate of Discordance Mean % Error* p 25 (n575) 9.7% 21.9% 23.0% -4.1% reference .......................................................................................................................................................................................... 25-30 (n683) 10.1% 26.5% 23.1% -4.7% .47 .......................................................................................................................................................................................... >30 (n1,304) 12.3% 28.6% 23.5% -4.0% .91 .......................................................................................................................................................................................... * For patients delivering within 3 weeks of ultrasound 354 Evaluating the influence of maternal obesity on the screening efficiency of sonographic markers for the prediction of Down syndrome Katherine Goetzinger 1 , Alison Cahill 1 , George Macones 1 , Anthony Odibo 1 1 Washington University in St. Louis, St. Louis, MO OBJECTIVE: To determine the effect of maternal obesity on the screen- ing efficiency of sonographic markers for the prediction of trisomy 21 (T21). STUDY DESIGN: This is a retrospective cohort study of patients present- ing for second trimester genetic ultrasound to our large tertiary cen- ter. Both major anomalies (cardiac defects, duodenal atresia, and ven- triculomegaly) and minor sonographic markers for T21 (cystic hygroma, nuchal edema, echogenic bowel, renal pyelectasis, echo- genic intracardiac focus, and short femur/humerus length) were eval- uated. In patients with trisomy 21, the proportion of each identified marker was compared between patients with a body mass index (BMI) 30 and 30 using chi-square and Fisher’s exact tests. The sensitivity, specificity, likelihood ratios (LR) and their 95% confidence intervals (CI) were then calculated for the association of all major anomalies and all minor markers with T21, stratified by maternal BMI. Statistical significance was determined by evaluating for non-overlapping con- fidence intervals. RESULTS: Of 53,340 patients with complete outcome data, there were 179 (0.3%) cases of T21. 149 cases were in patients with a BMI30 and 30 cases were in patients with a BMI30. In patients with T21, the proportion of both major anomalies and minor markers was similar between patients with a BMI30 and BMI30. (major: 22.8% v. 10.0%, p=0.14; minor: 47.0% v. 46.7%, p=0.97) There was no statis- tically significant difference in sensitivity, LR+, and LR- for both ma- jor anomalies and minor markers for the prediction of T21 across BMI categories. A statistically significant higher specificity for both major anomalies and minor markers was observed in patients with a BMI30 compared to BMI30, although this difference may not be clinically significant. CONCLUSIONS: Maternal obesity does not affect the screening effi- ciency of second trimester sonographic markers for T21. Patient counseling on risk assessment for T21 based on ultrasonographic findings need not be altered on the basis of BMI. T21 Marker BMI Sensitivity (95% CI) Specificity (95% CI) LR (95% CI) LR (95% CI) Any Major Anomaly 30 22.8% (16.3-30.4) 99.3% (99.2-99.4) 31.8 (23.2-43.6) 0.8 (0.7-0.8) .......................................................................................................................................................................................... 30 10.0% (2.1-26.5) 99.6% (99.5-99.7) 24.9 (8.2-75.8) 0.9 (0.8-1.0) .......................................................................................................................................................................................... Any Minor Marker 30 47.0% (38.8-55.3) 86.5% (86.2-86.8) 3.5 (2.9-4.1) 0.6 (0.5-0.7) .......................................................................................................................................................................................... 30 46.7% (28.3-65.7) 88.9% (88.3-89.5) 4.2 (2.9-6.2) 0.6 (0.4-0.8) .......................................................................................................................................................................................... 355 In vivo MRI assesment of placental perfusion and oxygenation in a rat model of intra uterine growth restriction (IUGR) Benjamin Deloison 1 , Sabine Aimot 1 , Nathalie Siauve 2 , Gihad Chalouhi 1 , Rokhaya Thiam 3 , Daniel Balvay 3 , Olivier Clement 2 , Yves Ville 4 , Laurent Julien Salomon 1 1 Faculte de medecine, Universite Paris-Descartes, AP-HP, Hopital Necker- Enfants-Malades, Paris, 2 Faculte de medecine, Universite Paris-Descartes, AP-HP, HEGP, Paris, 3 Inserm U970, Paris, 4 Universite Paris Descartes, Paris OBJECTIVE: We examined the feasibility of placental perfusion mea- surement with MRI and superparamagnetic iron oxide (SPIO) in a rat model of intra-uterine growth restriction (IUGR). We also sought to non-invasively evaluate placental oxygenation using Blood Oxygen Level Dependant (BOLD) contrast imaging. STUDY DESIGN: Thirty-two rats at 16 days of gestation underwent sur- gical ligation of the left uterine vessel to induce IUGR. Eighteen rats were examined by MRI three days later, using a multi-section FSPGR sequence after bolus injection of SPIO. Signal intensities were mea- sured in the maternal left ventricle and the placenta of both horns. Quantitative microcirculation parameters were calculated and com- pared between the placentas of the two horns. In 22 rats, the signal intensity of maternal liver, healthy and pathological foeto-placental units before and after maternal hyperoxygenation was also measured with a FIESTA sequence. RESULTS: Mean weight of fetuses was 4.320.66g and 3.490.56g in the right and left uterine horn respectively (p0.001). Fifty-four ki- netic curves of placental perfusion were obtained and mean placental blood flow was significantly lower in the left horns than in the normal horns (159.4 +/- 54.6 vs 108.1 +/- 41 ml/min/100g, p=0.0004). Under hyperoxygenation a significant increase of BOLD signal inten- sity was observed in liver (+12%, n=18), healthy placenta (+20%, Poster Session II Diabetes, Labor, Ultrasound-Imaging www.AJOG.org S144 American Journal of Obstetrics & Gynecology Supplement to JANUARY 2011