Morphological characteristics of monochorionic twin placentas, the number, diameter and distribution of arterio-arterial (AA), veno-venous (VV), arterio-venous (AV), and veno-arterial (VA) anastomoses, and the potential impact of placental pathology on maternal and fetal complications in monochorionic twin pregnancies

Objective: The aim of this study was to evaluate the morphological characteristics and vascular anastomotic patterns AA, VV, AV, and VA in monochorionic twin placentas in terms of their number, diameter, and distribution, and to investigate their possible association with maternal and fetal complications. Materials and Methods: Twenty monochorionic twin placentas, delivered at Akdeniz University Hospital and preserved with macroscopic integrity for postnatal examination, were prospectively included in the study. Clinical and obstetric data—including maternal age, gravida, parity, BMI, gestational age at delivery, birthweights, fetal sex, Doppler findings (MCA MoM, umbilical artery PI), EFW discordance, and birthweight discordance—were recorded. Placental weight and surface area, placental sharing ratios for each twin, placental sharing discordance, and birthweight-to-placental area ratios were calculated. The number and diameters of AA, AV, VV, and VA anastomoses were measured and documented. Cases were classified into TTTS, TAPS, sFGR, and NC groups. In addition, the application of fetoscopic laser therapy was noted and analyzed. Intergroup comparisons were performed using the Mann–Whitney U test, and p<0.05 was considered statistically significant. Results: The median gestational age at delivery in the TTTS group was 22 weeks, significantly lower than in the NC group (p=0.018). Although the placental sharing ratio and sharing discordance were higher in the TTTS group, statistical significance was not reached (p=0.390 and p=0.445, respectively). The birthweight-to-placental sharing ratio was lower in the TTTS group (median: 0.78). Vascular analysis showed a predominance of thick AV anastomoses in the TTTS group, while AA anastomoses were either absent or very narrow. In the TAPS group, ∆MCA MoM was notably high (median: 1.31), consistent with diagnostic criteria. In sFGR cases, placental territory for the smaller twin was reduced to as low as 25%, with birthweight discordance exceeding 30% in some cases. Most cases undergoing fetoscopic laser therapy had TTTS, and despite earlier delivery, higher neonatal survival was observed in this group. Conclusion: The findings of this study suggest that placental sharing patterns and vascular anastomotic configurations may play a role in the development of complications in monochorionic twin pregnancies. Particularly in TTTS cases, early delivery, younger maternal age, dominant AV anastomoses, and insufficient AA connections were notable. However, due to the limited sample size, definitive conclusions cannot be drawn. These results may serve as hypothesis-generating data for future studies. Keywords: Monochorionic twin pregnancy, placental anastomosis, TTTS, TAPS, sFGR, fetoscopic laser, placental sharing, perinatal complication