17th World Congress on Ultrasound in Obstetrics and Gynecology Poster abstracts Methods: We measured biparietal diameter (BPD), femur length (FL), TC and AC in 57 women at 20 to 41 weeks of gestation. They had no fetal anomalies affecting fetal biometry. The equation between AC and TC was obtained by regression analysis. Then, we compared EFW calculated using mAC with that using cAC from the equation in fetuses with abdominal wall defect or ascites. Results: (1) We obtained the equation by regression analysis in fetuses without anomalies affecting AC. AC = 1.151 × TC + 1.984 (R 2 = 0.869, P < 0.001) (2) In cases of fetal anomalies such as abdominal wall defect or ascites, EFW using cAC from the equation was more accurate than EFW using mAC. Conclusions: The ratio AC to TC is relatively constant regardless of gestational age beyond second trimester. cAC calculated from TC instead of mAC is more accurate to estimate fetal weight and may improve to detect abnormal fetal growth in fetuses who are affected by abdominal wall defect or ascites. P34.02 Macrosomia: a new formula for optimized fetal weight estimation N. C. Hart , J. Siemer, M. Schrauder, B. Meurer, T. W. Goecke, R. L. Schild University Hospital Erlangen, Germany Objectives: The incidence of fetal macrosomia has been constantly increasing in recent years, and along with it the associated risks for mother and child. To ensure that the method of obstetric management associated with the lowest possible risk can be selected, precise prenatal weight estimation by sonographic fetal biometry is necessary. The aim of this study was to develop and evaluate a new specific formula for estimating weight in the macrosomic fetus. Methods: Complete sonographic biometries were carried out within one week of delivery in 312 singleton fetuses with a birth weight of 4000 g or more. Exclusion criteria were intrauterine death, and major structural or chromosomal anomalies. After a new ‘best-fit’ formula had been developed by stepwise regression analysis of fetal and maternal parameters in a formula-finding group (n = 155), it was prospectively compared with currently available weight equations (formula evaluation group, n = 157). Results: The newly adjusted formula includes fetal femur length and abdominal circumference, as well as maternal weight. It proved to be superior to established equations, when studied in the evaluation group. Conclusion: The new formula allows better weight estimation in the macrosomic fetus. P34.03 New formulae for estimating fetal weight for specific birth weight groups J. Siemer , N. C. Hart, N. Egger, T. Wolf, T. W. Goecke, R. L. Schild University Hospital Erlangen, Department of Obstetrics and Gynaecology, Germany Objectives: There are several commonly used formulae for estimating fetal weight by sonographic biometry. The majority of them were derived from relatively small samples, with a narrow range of birth weights (mostly term fetuses). The aim of this study was to develop new formulae for specific birth weight groups to improve accuracy of estimation. Methods: Ultrasound examinations and fetal biometries were carried out within one week of delivery in 3511 singleton fetuses with a birth weight of less than 4000 g. Further exclusion criteria were intrauterine death, and major structural or chromosomal anomalies. Two subgroups were built (fetuses with a birth weight up to 2500 g and with more than 2500 g). For each subgroup, biometry data of half of the populations was used for stepwise regression analysis to identify best-fit formulae for predicting fetal weight at birth. Eventually, the new formulae were evaluated in the other half of the populations of the subgroups and were compared with commonly used formulae. Results: The new weight specific formulae proved to be superior to the established weight formulae. Conclusion: Formulae that focus on certain subgroups of fetuses are able to improve accuracy of fetal weight estimation. P34.04 Second trimester prediction of birth weight using individualized growth assessment W. Lee 1 , R. L. Deter 2 , S. Sameera 1 , M. D. Powell 1 , B. F. McNie 1 , J. Espinoza 3 , R. Romero 4 1 William Beaumont Hospital, United States, 2 Baylor College of Medicine, United States, 3 Wayne State University, United States, 4 Perinatology Research Branch, United States Objectives: To re-examine the use of Individualized Growth Assessment (IGA) in predicting BW with standard EWT functions and those utilizing soft tissue parameters. Methods: A prospective longitudinal study of 44 fetuses was performed using 3D ultrasound. Standard biometry (BPD, AC, FDL), soft tissue parameters (fractional arm, AVol, and thigh volume, TVol) and head (A) and abdominal (B) cubes were measured. Using 2nd trimester data, growth models were specified that predicted sonographic parameters at 38 weeks and at actual birth age. An EWT function based on A and B (Deter RL, et al. JCU 1989; 17 : 83–88) and functions that included AVol or TVol (Lee W, et al. UOG 2006; 28 : 389) were applied. Actual and predicted BW’s were compared. Mean and SD of % differences were taken as measures of systematic and random prediction errors, the former evaluated by t-test and the latter by F-test. Results: 44 infants were delivered with BW of 3332 ± 397 g, at 38.8 ± 1.3 weeks, MA. In 26, the interval between 38 weeks and delivery was > 0.5 weeks permitting evaluation of Growth Cessation (GC) vs. Growth-To-Delivery (GTD) assumptions. GC and GTD groups were defined, depending on which assumption gave % differences closer to the ideal value of zero. All systematic errors greater than 4.0% were statistically significant from zero. All GTD fetuses identified by the latter 3 EWT methods were detected by the A,B EWT method. Conclusions: Two main growth patterns occurred after 38 weeks. The A, B EWT function effectively identified these patterns and gave BW predictions for each that were similar to those obtained previously, greater than 12 weeks before delivery. All subjects − % difference Subgroups − % difference Est Weight Function N 38 wks Birth Age N GC N GTD A, B 44 −3.2 ± 11.0 5.1 ± 10.3 13 −0.2 ± 5.6 13 0.8 ± 5.1 BPD, AC, FDL 44 15.8 ± 14.0 24.6 ± 14.8 24 12.6 ± 11.1 2 −0.6 ± 5.6 BPD, AC, AVol 44 5.9 ± 12.3 14.6 ± 13.7 22 5.1 ± 8.9 4 −0.6 ± 4.8 BPD, AC, TVol 44 3.3 ± 11.0 11.7 ± 12.5 19 4.1 ± 9.0 7 1.3 ± 4.5 P34.05 Customized standards of estimated fetal weight as predictor of adverse perinatal outcome A. Iraola , E. Eixarch, E. Meler, M. Illa, F. Figueras, E. Gratac ´ os Hospital Clinic, Barcelona, Spain Objectives: To evaluate the predictive capacity of middle cerebral artery, umbilical artery and customized standards of estimated fetal 582 Ultrasound in Obstetrics & Gynecology 2007; 30: 547–653