Objectives To review experience with fetoscopic laser ablation of placental anastomoses to treat monochorionic diamniotic (MCDA) twin pregnancies complicated by twin-to-twin transfusion syndrome (TTTS) in a single centre over a ten-year period. Methods A retrospective study on 142 MCDA twin pregnancies complicates by TTTS treated with equatorial laser ablation of placental anastomoses (2008–2018). Solomon technique was also applied after 2013. Survival rates, neonatal outcome, intraoperative and post-laser complications were recorded, and prognostic factors analysed. Results A total of 133 cases were included in the final analysis; 41 patients were at stage II (30.8%), 73 were at stage III (62.9%), while only 12 (9%) at stage I and two patients (1.7%) at stage IV. Solomon technique was applied in 39 cases (29.3%). Survival of both twins was 51.1% (68/133), of a single twin 20.3% (27/133), and of at least one 71.5% (95/133), with an overall survival of 61.3% (163/266). TAPS and recurrent TTTS occurred in 8 (6%) and 15 (11.3%) patients. Survival of both fetuses increased over time (44.6 vs. 57.3%). A posterior placenta (p<0.003) and the use of the Solomon technique (p<0.02) were more frequent in cases with survival of both fetuses, while TTTS recurrence was significantly associated to the loss of one or two fetuses (p<0.01). Such associations were confirmed at logistic regression analysis. Conclusions Survival of both twins can improve over time and seems to be favourably associated with a placenta in the posterior location and the use of the Solomon technique.

Virtual poster abstracts the fetus was noted to be homozygous for both parental pathogenic mutations. WES is notable for increasing the ability to provide diagnostic capabilities in fetuses with sonographic abnormalities due to rare disorders. The identification of the abnormal gene will help to offer either preimplantation genetic diagnosis or prenatal invasive testing in these couples. VP33.09 Exome sequencing versus gene panels for non-immune hydrops fetalis

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Virtual poster abstracts Ultrasound (US) fetal biometry and feto-maternal Doppler were performed within 72h from admission. For longitudinal growth assessment we calculated EFW z-velocity between the EFW z-score at recruitment US and neonatal weight z-score. Results: We found no differences in maternal baseline characteristics, except maternal age, significantly higher in PPROM patients than in PTL group (p = 0,012), and smoking habit, significantly higher in PPROM than in the uncomplicated group (p = 0,038). Gestational age at first US was significantly lower in PTL and PPROM groups (p < 0,001). SGA was significantly more frequent in fetuses from PTL and PPROM mothers than in the uncomplicated group (PTL p = 0,009; PPROM p = 0,011). There were no significant differences in the umbilical artery pulsatility index (PI), middle cerebral artery PI, uterine artery PI and cerebro-placental ratio among the groups. As expected, women with PTL or PPROM presented earlier GA at delivery (PTL p < 0,001; PPROM p < 0,001). SGA neonates were significantly more frequent in women with PPROM than in the uncomplicated group (p = 0,02). The analysis did not show statistically significant differences in EFW z-velocity. Conclusions: Our data show a higher proportion of SGA fetuses at admission due to PTL or PPROM and a higher proportion of SGA at delivery in women with PPROM as compared to uncomplicated patients. This is a exploratory study showing very preliminary data from a cohort planned to be finished for recruitment in two years. More research is needed to confirm the results and to clarify the causes. VP38.06 Effect of delivery mode on neonatal outcomes in smallfor-gestational-age fetuses

The aim of this study is to describe the perinatal outcomes associated to FGR in a portuguese tertiary referral unit and to compare two consecutively implemented protocols (before and after February 2019). Methods: Retrospective study of singleton pregnancies diagnosed with FGR who delivered between 2018 and 2019 in Santa Maria Hospital. In our department, before February 2019, the delivery of a growth restricted fetus was programd for 37 weeks and it was anticipated if the pulsatility index of the ductus venosus (DV) was >95th centile from 28 weeks or if the umbilical artery end diastolic flow (UAEDF) was inverted from 32 or absent from 34 weeks. After February 2019, the delivery is anticipated if the A wave of the DV is absent or inverted from 26 weeks or if the UAEDF is reversed from 32 or absent from 34 weeks. We evaluated and compared obstetric and neonatal outcomes.