10–14 October 2010, Prague, Czech Republic Oral communication abstracts Methods: Patients with singleton pregnancies at term in the second stage of labor underwent serial sonographic examination. Obstetric management was decided on the basis of the clinical examinations. Results: Seventy-six patients (59 para 0) were enrolled. Of those that were delivered vaginally, 14 had a posterior occiput and were excluded from the analysis. In the remaining cases, serial examination revealed the passage of the fetal occiput below the symphysis in 36/44. In the infrapubic scan this resulted in a typical image (Figure 1). Vaginal examination performed at the time of this observation demonstrated in all these cases a station > +3 cms and a rotation < 45 ◦ . In 24 patients spontaneous vaginal delivery occurred in 11 + 7 (range 3–25) minutes. In 12 cases a vacuum was applied, and this was always classified as outlet according to ACOG. Conclusions: Demonstration with an infrapubic scan that the fetal occiput is below the pubic symphysis is an objective sign of imminent vaginal delivery. If a vaginal extraction becomes necessary, the procedure can be classified as an outlet one, with virtually no added risk over that of a spontaneous delivery. Supporting information can be found in the online version of this abstract. Fig. 1. Multiplanar evaluation of a 3D volume obtained from an infrapubic scan in a patient in advanced second stage of labor (station +3 cms and rotation < 45 ◦ by digital examination): a) in the longitudinal scan the curvature of the fetal skull demonstrates that the occiput is below the level of the symphysis; b) visualization of the midline echo in the corresponding transverse scan suggests that the rotation is < 45 ◦ . OC15: MULTIPLE PREGNANCY OC15.01 Prenatal determination of placental cord insertion site in monochorionic and dichorionic twin gestations: a predictor of growth discordance? F. Breathnach 1,3 , F. McAuliffe 2 , M. Geary 3 , S. Daly 4 , J. Higgins 5 , J. J. Dornan 6 , J. J. Morrison 7 , G. Burke 8 , S. Higgins 9 , S. Carroll 2 , F. Malone 1,3 1 Obstetrics and Gynaecology, Royal College of Surgeons in Ireland, Dublin 1, Ireland; 2 National Maternity Hospital, Dublin, Ireland; 3 Rotunda Hospital, Dublin, Ireland; 4 Coombe Womens and Infants University Hospital, Dublin, Ireland; 5 Cork University Maternity Hospital, Dublin, Ireland; 6 Royal Victoria Maternity Hospital, Belfast, Ireland; 7 University College Hospital, Galway, Ireland; 8 Mid Western Regional Maternity Hospital, Limerick, Ireland; 9 Our Lady of Lourdes Hospital, Drogheda, Ireland Objectives: To determine the utility of prenatal identification of placental cord insertion site as a possible proxy marker for subsequent development of intratwin growth discordance in monochorionic and in dichorionic twin gestations. Methods: The ESPRIT trial is a national prospective population study of 1038 consecutive twin pregnancies managed and delivered at 8 tertiary referral centers in one country. All pregnancies were followed using a uniform sonographic surveillance protocol and were delivered at one of 8 designated centers. Sonographic determination of placental cord insertion site was recorded at enrollment (11–22 weeks’ gestation) and at follow-up serial evaluation. Perinatal outcomes for all participants were recorded onto a central consolidated web-based database. Placental pathology was available for correlation. Twin pregnancies were grouped according to placental cord insertion site in each twin pair (central- central; central-noncentral; and noncentral-noncentral). Results: This study was completed by 1022 participants, and outcome data was obtained for 998 patients (98%). Eighty percent of the cohort (862) was dichorionic. On prenatal sonographic evaluation, the placental cord insertion site was recorded as central, marginal or velamentous for 73%, 16% and 3% of twin fetuses respectively. The latter 2 descriptions were considered noncentral for the purpose of this analysis. Placental cord insertion site could not be confirmed on prenatal sonographic evaluation in 8% of cases. Cord insertion site other than central correlated with monochorionic gestation (P = 0.0074). Prenatal identification of a noncentral cord insertion in either one or both fetuses of a twin pair correlated with birth weight discordance of ≥ 20% (P = 0.0115). Conclusions: Prenatal sonographic evidence of a marginal or velamentous cord insertion in either one or both twins correlates with subsequent intratwin birth weight discordance and may merit a strategy of heightened fetal growth surveillance in such pregnancies. OC15.02 Twin pregnancy: screening test for spontaneous preterm delivery and preeclampsia during the second trimester of pregnancy M. Parra-Cordero , M. Rodr´ ıguez, R. D´ ıaz, G. Rencoret, E. Vald´ es, H. Mu ˜ noz Fetal Medicine Unit, Obstetric & Gynecology Department, University of Chile, Santiago, Chile Objectives: To evaluate the role of ultrasound cervical length and uterine artery Doppler at 20+0 to 24+6 weeks gestation as predictors of spontaneous early preterm birth (sPTD) and preeclampsia (PET) in twin pregnancies. Methods: This is an ongoing prospective study involving 8,280 pregnancies who underwent standardized transvaginal scan for evaluation of cervical length (CL) and uterine artery (UtA) Doppler at 20+0–24+6, including 130 twin pregnancies (1.6%). Maternal characteristics and ultrasound variables were studied using a multiple regression analysis as predictor of either sPTD before 35 weeks or developed PET in twin pregnancies. Results: The rate of sPTD before 35 weeks and PET in twin pregnancies was 26.9% and 12.3%, respectively, both significantly higher than singleton pregnancies. UtA Doppler was not significantly different in women who later developed PET and control in twin pregnancy, whereas nulliparity was significantly associated with this outcome (OR = 4.8 [1.4–16.6]; P < 0.05). On the other hand, logistic regression analysis showed that CL was the best predictor for sPTD before 35 weeks in twin pregnancy, having a detection rate and false positive rate of 25% and 4%, respectively, for a CL of 25 mm. Conclusions: This study corroborates that twin pregnancies are a high risk group for spontaneous and iatrogenic preterm delivery. Although UtA Doppler showed not to be useful in predict these outcomes, CL was highly associated with spontaneous preterm delivery. Supported by Fondecyt 1090245. OC15.03 Intratwin weight discordance and the prediction of successful vaginal twin birth: the ESPRiT study F. Breathnach 1,3 , F. McAuliffe 2 , M. Geary 3 , S. Daly 4 , J. Higgins 5 , J. Dornan 6 , J. J. Morrison 7 , G. Burke 8 , S. Higgins 9 , S. Carroll 2 , F. Malone 1,3 1 Obstetrics and Gynaecology, Royal College of Surgeons in Ireland, Dublin 1, Ireland; 2 National Maternity Hospital, Dublin, Ireland; 3 Rotunda Hospital, Dublin, Ireland; 4 Coombe Womens and Infants University Hospital, Dublin, Ireland; 5 Cork University Maternity Hospital, Dublin, Ireland; 6 Royal Victoria Maternity Hospital, Belfast, Ireland; 7 University College Hospital Galway, Belfast, Ireland; 8 Mid Western Regional Maternity Hospital, Limerick, Ireland; 9 Our Lady of Lourdes Hospital, Drogheda, Ireland Objectives: The optimal mode of delivery for twins is a contentious issue. Intratwin weight discordance may increase the prospect of Ultrasound in Obstetrics & Gynecology 2010; 36 (Suppl. 1): 1–51 29