Proximate cord insertion in monochorionic twins with selective fetal growth restriction

Background: Monochorionic (MC) twins share a single placenta which can be unequally shared, leading to selective fetal growth restriction (sFGR). Limited data is available on the prevalence and clinical consequences of proximate cord insertion (PCI) in sFGR pregnancies.

Objective: We aimed to investigate the prevalence of PCI in MC placentas with and without sFGR and per type of sFGR, and study the placental characteristics and perinatal outcome of PCI in sFGR pregnancies.

Study design: In this multicenter retrospective cohort study, we included all consecutive placentas of MC twin pregnancies with and without sFGR evaluated between 2002-2023. We excluded MC twins with twin-twin transfusion syndrome, twin anemia polycythemia sequence and monoamnionicity. Our primary outcome included the prevalence of PCI (distance between cord insertions ≤4 cm) and type of cord insertions categorized as concordant, intermediate or discordant. Secondary outcomes consisted of type and size of placental vascular anastomoses and short-term clinical outcomes including fetal demise and birth weight discordance (BWD).

Results: Of 813 MC placentas, 468 were from uncomplicated twins and 345 from sFGR twins (187 type I, 41 type II and 117 type III sFGR). The prevalence of PCI in uncomplicated versus sFGR placentas was 3.8% (18/468) and 4.6% (16/345), respectively (p=0.58). PCI in sFGR type I, II and III was detected in 0.5% (1/187), 0% (0/41) and 12.8% (15/117), respectively (p<0.0001). The prevalence of discordant cord insertions (velamentous-paracentral) in uncomplicated twin placentas and sFGR placentas was 19.9% (93/468) and 45.5% (157/345), respectively (p<0.0001). Diameter of arterio-arterial (AA) anastomoses in sFGR placentas with and without PCI was 3.0 mm (IQR 2.7-5.0) versus 2.2 mm (IQR 1.4-3.1; p<0.0061). BWD in sFGR twins with PCI was 18.5% (IQR 16.4-21.0) and without PCI was 28.0% (IQR 21.8-35.9; p<0.0001). Fetal demise occurred in 12.5% (2/16) of pregnancies with PCI and 6.1% (20/329) of sFGR pregnancies without PCI (p=0.27).

Conclusion: sFGR type III placentas exhibit a high prevalence of PCI, requiring increased awareness due to the presence of larger AA anastomoses and a potentially higher risk of fetal demise.