20–24 October 2018, Singapore Short oral presentation abstracts Objectives: Conventional weight-based criteria for neonatal growth restriction (GR) do not account for the growth potential of an individual fetus, nor do they effectively separate constitutionally small fetuses from ones that are malnourished. Individualised growth assessment (IGA) uses 2nd trimester (TM) growth velocity of anatomical size parameters as an estimate of growth potential in an individual fetus to evaluate third TM fetal growth and neonatal growth outcome. We hypothesized that differences in maternal body composition and/or energetics can be detected when individual fetuses are categorised by the presence or absence of GR. Methods: Serial 2D fetal biometry (BPD, HC, AC, FDL) and neonatal measurements were obtained in 20 women with dichorionic-diamniotic (DCDA) pregnancies. Based on IGA, 10 women had at least one GR infant and were compared to 10 others with no neonatal GR. Changes in maternal body composition (fat free mass and fat mass) were estimated from total body water (TBW) using deuterium dilution, body volume by air displacement plethysmography, and total body potassium/protein by whole body counting. Energetic changes in resting energy expenditure by respiration calorimetry, total energy expenditure by doubly labelled water, and physical activity level were measured. Comparisons between groups were made at each TM adjusted for GA at delivery and prepregnancy BMI. Results: Lower accretion of maternal fat-free mass in the first TM as well as lower accretion of body protein in the second TM were associated with infant GR (p=0.01, p=0.02, respectively). No association was seen with gestational weight gain, fat mass, TBW, resting energy expenditure, total energy expenditure, and physical activity. Conclusions: Suboptimal gestational weight gain (Institute of Medicine) has been linked to low birth weight in DCDA pregnancies. Lower accretion of maternal fat free mass and total body protein may represent the major components of gestational weight gain with neonatal GR in DCDA twins. OP14.02 Estimation of fetal weight at term: comparison of the INTERGROWTH and Hadlock formulas J. Stirneman 1,3 , S. Guterman 2 , M. Guiot 2 , J. Busson 2 , Y. Ville 4,3 , L.J. Salomon 5,3 1 Obstetrics and Maternal-Fetal Medicine, GHU Necker Enfants Malades, APHP, Universit´ e Paris Descartes, Paris, France; 2 Necker Enfants Malades Hospital, APHP, Paris V University, Paris, France; 3 EHU PACT, Institut Imagine, Paris Descartes, Paris, France; 4 Paris Descartes University, Paris, France; 5 Maternit´ e, H ˆ opital Necker Enfants Malades, APHP, Universit´ e Paris Descartes, Paris, France Objectives: To describe the performance of the INTERGROWTH (IG) and the Hadlock formulas for the estimation of fetal weight at term. Methods: Retrospective analysis of low-risk pregnancies delivered at 38+0 – 41+0 weeks with an ultrasound in the week before delivery in a single institution over a 6-month period. The estimated fetal weight (EFW) was calculated by the Hadlock formula (abdominal circumference, head circumference and femur length) and by the IG formula (abdominal and head circumference) and compared to birthweight (BW) using absolute percent error (APE) defined as abs(100*(EFW-BW)/BW). Results: 547 pregnancies were included. Median birthweight was 3355 g (IQR = 3040 – 3615). Median time interval between ultrasound and delivery was 2 days (IQR = 1 – 3). Median APE was 6.3% and 5.5% with the IG and Hadlock formulas respectively and the 95 th centile were 18.5% and 15.5% respectively. The IG formula underestimated birthweights >3200 g whereas Hadlock overestimated lighter newborns and underestimated heavier ones (figure). Conclusions: Small discrepancies in performance exist between Hadlock and IG formulas for EFW. The significance of these discrepancies should be explored. Supporting information can be found in the online version of this abstract OP14.03 Comparison of the accuracy of INTERGROWTH-21 formula with other ultrasound formulae in fetal weight estimation C.W. Kong, W. To Obstetrics and Gynecology, United Christian Hospital, Hong Kong Objectives: To compare the accuracy of the newly developed ultrasound formula from INTERGROWTH-21st project in fetal weight estimation with the traditional Hadlock1 and Shepard formula, and to explore any factors that affect the accuracy of these formulae. Methods: All Chinese pregnant patients with singleton pregnancies who had delivery in United Christian Hospital between January to December 2016 were retrospectively reviewed. Those who had prenatal ultrasound scan performed within 7 days of delivery were recruited. Hadlock1, Shepard and INTERGROWTH-21 formula were then used to estimate the fetal weight and their accuracies were compared with the actual birthweight of the neonates. Results: A total of 403 patients were recruited for final analysis. Hadlock1 formula was the most accurate with the lowest mean absolute percentage error (MAPE) 7.34 when compared with Shepard (9.00; p<0.001) and INTERGROWTH-21 formula (9.07; p<0.001). The performance of INTERGROWTH-21 formula was inferior to the traditional formulae, with the lowest proportion of patients having estimated fetal weight within 10% discrepancy from the actual birthweight (57.6%) compared with Hadlock1 (71.2%; p<0.001) and Shepard formulae (66.3; p=0.011). Presence of intrauterine growth restriction (IUGR) or fetal macrosomia (>=4000g) were both associated with significantly higher MAPE in Hadlock1 and INTERGROWTH-21 formula. IUGR (p=0.005) and macrosomia (p=0.004) remained significant in the final equation of logistic regression model that affect the precision of fetal weight estimation when Hadlock1 formula was used, while only IUGR was significant when INTERGROWTH-21 formula was used (p<0.001). Maternal obesity, oligohydramnios, fetal presentation and placental location were not shown to affect the accuracy in all the three formulae. Conclusions: INTERGROWTH-21 formula was not shown to be better than the traditional Hadlock1 or Shepard formulae. Future prospective studies would be required to evaluate the accuracy of INTERGROWTH-21 formula especially at the extremes of birthweight. OP14. 04 Fetal ultrasound at 36 weeks can accurately predict neonatal body composition in women who are overweight and obese C.M. O’Brien 2,1 , R. Grivell 2,3 , A. Deussen 2 , J. Louise 2 , J. Dodd 2,3 1 Fetal Medicine Unit, RPA Women and Babies, Camperdown, NSW, Australia; 2 University of Adelaide, Robinson Institute, North Adelaide, SA, Australia; 3 Department of Perinatal Medicine, Women’s and Babies’ Division, Women’s and Children’s Hospital, Adelaide, SA, Australia Objectives: Advances in ultrasound technology have increased interest in measurement and prediction of fetal overgrowth and  The Authors 2018  Ultrasound in Obstetrics & Gynecology 2018; 52 (Suppl. 1): 66–137. 105