Objectives: Evaluation of the advantages and limitations of routine screening in early pregnancy by transvaginal sonography (TVS) in an unselected population. Methods: A routine ultrasound examination was offered to every woman in the 12th week of her pregnancy using a transvaginal probe. The examination protocol was focused on searching for major structural anomalies. Routine transabdominal screening at 18 and 32 weeks was also performed. Anomalies were divided into three groups. Group 1: all cases were diagnosed; Group 2: only a certain percent of the cases were detected; Group 3: not detected. Diagnoses were confirmed by neonatological and pathological examinations. Results: In a twenty-year period 13 835 women were examined and 198 fetuses had malformations. Fetal anomalies were diagnosed in 78 cases at the 12th week (39.4%), 49 cases at 18 weeks (24.7%), 56 cases at 32 weeks (28.3%) and 15 cases later. All those malformations which cause severe defects and/or extensions of the body contour were detected (Group 1). Structural anomalies which can be diagnosed as a consequence of obstruction or stenosis and those causing small defects were recognised only in a certain percent of cases (Group 2). The explanation for the failure to detect the anomalies included in Groups 2 and 3 is discussed. Conclusions: Early transvaginal screening offers the possibility of early termination of pregnancies with severe structural anomalies in 39.4% of cases. However, standard mid-second-trimester transabdominal scanning is still recommended since a significant number of malformations cannot be detected so early in pregnancy. (a) There are malformations which do not manifest so early in pregnancy; (b) we do not have enough experience of the early pathological changes of these anomalies; (c) the resolution of the transvaginal probe is still not enough to recognise them. OP25.12Nuchal translucency reference range curve in Quito, Ecuador Objectives: To assess the behavior of nuchal translucency (NT) and crown-rump length (CRL) in the population of the Quito, Ecuador, at 2800 m above sea level, during weeks 11 to 14 of pregnancy and to compare with the normality range of the Fetal Medicine Foundation to establish a reference range for this population. Methods: A transversal study was performed in 602 fetuses that presented with a normal karyotype or phenotype. All the fetuses underwent measurement of NT during routine ultrasound examination. Student's t-test and percentilation with dispersion tables were used in the statistical analysis. The regression test was used to find a better mathematical model to describe the NT behavior. Results: 602 gestations with a CRL between 45 and 84 mm with a normal karyotype and perinatal follow-up were included in the study. Interval analysis of gestational age through regression models suggests that the power used should be between 0.5 and 1 (Table). Use of the 95 th percentile allowed us to include the patient with the highest NT. Results: In 10 twin pregnancies, one of the fetuses was found to h...

Objectives: To evaluate the posterior fossa in fetuses with normal and chromosomal abnormalities at 11-13 + 6 weeks' gestation Methods: To measure the brain stem (BS) and brain stem to occipital (BSOB) in fetuses of 518 normal, and trisomy 13, 18, 21 and 45, XO in 8, 26, 38, 8 respective in singleton pregnancies at the first trimester between 11 and 13 + 6 weeks. All cases underwent fetal karyotyping using chorionic villus sampling or amniocentesis to confirm the fetus's normalcy. Results: In linear regression, BS and BSOB correlated significant linearly with CRL. (BS = 1.602 + 0.022CRL, R2 = 0.257, p value < 0.001), (BSOB = 2.588 + 0.033CRL, R2 = 0.247, p value < 0.001), (BS to BSOB ratio = 0.634-0.0002CRL, R2 = 0.001, p value = 0.577). The BS to BSOB ratio was below the 5 th percentile in 4(50%), 11(44%), 2(5.26%), and 4(50%) of trisomy 13, trisomy 18, trisomy 21 and 45, XO. In trisomy 13, trisomy 18 and 45, XO the BS and BS to BSOB ratio were significantly lower than in normal fetuses. But in the trisomy 21, BS, BSOB and the BS to BSOB ratio were no significant difference in normal fetuses. Conclusions: In the 11-13 + 6 weeks' scans, the many fetuses of the trisomy 13, 18, and 45, XO abnormalities posterior fossa, but trisomy 21 is no significant difference to euploid.