18–22 September 2011, Los Angeles, CA, USA Oral poster abstracts OP18.04 Impact of a new public screening policy for Down syndrome in Hong Kong: preliminary results K. Leung 1 , T. Lau 2 , M. Tang 3 , C. Lee 4 , W. Leung 5 , K. Au Yeung 6 , W. To 7 , W. Chan 8 , C. Lee 9 1 O&G, Queen Elizabeth Hospital, Hong Kong; 2 O&G, The Chinese University of Hong Kong, Hong Kong; 3 Prenatal Diagnostic and Counseling Department, Tsan Yuk Hospital, Hong Kong; 4 O&G, Queen Mary Hospital, University of Hong Kong, Hong Kong; 5 O&G, Kwong Wah Hospital, Hong Kong; 6 O&G, Tuen Mun Hospital, Hong Kong; 7 O&G, United Christian Hospital, Hong Kong; 8 O&G, Prince Margaret Hospital, Hong Kong; 9 O&G, Pamela Youde Nethersole Eastern Hospital, Hong Kong Objectives: To evaluate the impact of a universal screening strategy in the first trimester (including nuchal translucency, PAPP-A and β-HCG), introduced in all Hong Kong public hospitals during second half of 2010. Before July 2010, a prenatal screening or invasive test for Down syndrome was offered to women of 35 or above only. Methods: This was a cohort study in all eight public hospitals with an obstetric department with total annual deliveries of around 41,000, and two certified prenatal diagnostic laboratories in Hong Kong. All sonographers were trained. The numbers were extracted from the Down syndrome screening database; i.e. denominator was the number of women screened. The primary outcome was the number of Down syndrome diagnosed prenatally and postnatally, and the number of prenatal invasive procedures carried out. The secondary outcomes measured were the number of women screened, and false positive rate. Results: Compared to the second half of 2009, the number of Down syndrome diagnosed prenatally was increased from 9 to 21 in the second half of 2010. The number of women screened was increased from 3,971 to 14,355. The proportion of first trimester screening test was increased from 51.0% to 84.9%. The false positive rate was decreased from 9.0 to 5.6%. In one laboratory, the ratio of chorionic villus to amniotic fluid samples was increased from 0.23 to 0.96. Conclusions: Like the experience in other countries, the introduction of a universal combined risk assessment during the first trimester at a public level in Hong Kong increased the prenatal detection of Down syndrome. The impact on the number of infants born with Down syndrome, and the number of prenatal invasive procedures will be evaluated after further data collection. OP18.05 The effect of the contents of exomphalos and nuchal translucency (NT) at 11–14 weeks on the likelihood of associated chromosomal abnormality C. Iacovella 1 , E. Contro 2 , A. T. Papageorghiou 1 , T. Ghi 2 , G. Pilu 2 , B. Thilaganathan 1 , A. Bhide 1 1 Fetal Medicine Unit, St George’s Healthcare, London, United Kingdom; 2 Obstetrics & Gynaecology, Policlinico S.Orsola-Malpighi, Bologna, Italy Objectives: Previous publications suggest that exomphalos contain- ing the liver as less likely to be associated with aneuploidy as compared to that containing bowel alone. These publications did not take into account the influence of nuchal translucency. The objective of the study was to explore the influence of exom- phalos contents and nuchal translucency on the likelihood of aneuploidy. Methods: A retrospective search was conducted to identify all cases of exomphalos from the database of two fetal medicine units seen from 2001 till the end of 2010. Karyotype ascertained either prenatally or after birth. The data was arranged in two groups according to the presence or absence of aneuploidy, and the influence of exomphalos contents and nuchal translucency was examined. NT ≥ 3 mm was considered abnormally increased, and this data was converted in normal and increased NT. Results: A total of 79 fetuses with exomphalos were identified. NT was normal in 43 fetuses (54.4%). The exomphalos content was bowel alone in 60, and liver in the reminder. Aneuplody was observed in 44 fetuses. In 35 fetuses the karyotype was normal. Aneuploidy was significantly more common with exomphalos containing bowel alone (Table 1, Chi-squared = 5.9, P = 0.015). The effect of exomphalos content and nuchal translucency on likelihood of aneuploidy was explored using Logistic regression. It showed no significant independent contribution of exomphalos content on the likelihood of aneuploidy (P = 0.145. Abnormal NT increased the odds for aneuploidy by 6.6 (95% CI: 2.3 to 19.0). Conclusions: Both exomphalos containing bowel and increased NT are more likely to be associated with aneuploidy, but this is mainly due to NT. There is no independent effect of exomphalos content on the likelihood for aneuploidy. OP18.05: Table 1 Contents Karyotype Bowel Liver +Bowel Total Normal 22 13 35 Abnormal 38 6 44 60 19 79 OP18.06 First things first: preconditions to reliably estimate the risk of fetal trisomy R. Snijders 1,2 , M. Bakker 1 , E. Pajkrt 2 , A. Muller-Kobolt 1 , G. Sturk 2 , C. Bilardo 1 1 St Prenatale Screening, UMCG, Groningen, Netherlands; 2 St Prenatale Screening, AMC, Amsterdam, Netherlands Objectives: To evaluate reference ranges and settings used for first trimester assessment of the risk of fetal trisomy. Methods: Data from 13,399 consecutive singleton pregnancies, amongst which 50 trisomy 21, 23 trisomy 18 and 8 trisomy 13, were used to evaluate reference ranges used in Elipse and Astraia software. Results: Gestational age estimates in Elipse and Astraia were 1 to 2 days less than those obtained with the recommended reference curve in the UK and the Netherlands. In both software packages the expected number of trisomies was higher than the observed number (n = 81 compared to n = 87 in Astraia and n = 96 in Elipse), but the differences did not reach statistical significance. Standardized PAPP- A and bhCG values deviated significantly from 1.0; re-calculation of multiple of the medians (MoM) using reference curves recently published by Wright et al (2010) provided results close to 1.0 throughout the gestational age and maternal weight range. For the NT curve the original curves in Astraia and Elipse were similar and provided a median MoM of 1.0; the new curve proposed by Wright et al(2008) is relative high which results in a drop of the median mom to 0.93. Conclusions: Discrepancies in first risk estimates can be reduced if formulas and estimates used for calculation of gestational age and a-priory risks are unified. The next step in minimizing variation would be to unify the method by which PAPP-A, bhCG and NT measurements are standardized. It is proposed that reference curves from Wright et al (2010) are introduced for standardization of PAPP-A and bhCG as these fit the data better than current curves. For NT the original curve fits the data better than the updated one. The new curve may be appropriate for centres with high resolution equipment or centres that use the automated method for measuring NT. Ultrasound in Obstetrics & Gynecology 2011; 38 (Suppl. 1): 56–167 109