The Significance of Placental Cord Insertion Site in Twin Pregnancy.
Kalafat E., Thilaganathan B., Papageorghiou A., Bhide A., Khalil A.
OBJECTIVE: The aim of this study was to investigate the association between abnormal cord insertion and the development of the twin-specific complications, including birthweight discordance, selective fetal growth restriction (sFGR) and twin-to-twin transfusion syndrome (TTTS). METHODS: A single-center cohort study of twin pregnancies. Abnormal cord insertion was defined as either marginal (cord attachment site less than 2cm to the nearest margin of the placental disc) or velamentous (when the umbilical cord was attached to the membrane before reaching the placental disc with clear evidence of vessels traversing the membranes to connect with the placental disc), as described in placental pathology reports. Major structural or chromosomal abnormalities and monochorionic monoamniotic twins were not included in the study. Information on the pregnancies, ultrasound findings, prenatal investigation and interventions was obtained from the electronic ultrasound database, while data on the placental histopathological findings, pregnancy outcomes, mode of delivery, birthweight, gestational age at delivery, and admission to the neonatal intensive care unit (NICU) were obtained from the maternity records. Categorical variables were compared by the X2-test or Fisher's exact test, while continuous variables were compared using the t-test, analysis of variance (ANOVA) for multiple comparison and the Kruskal-Wallis test. RESULTS: 497 twin pregnancies, 351 (70.6%) dichorionic and 146 (29.3%) monochorionic, were included in the analysis. The incidence of birthweight discordance of 25% or more was significantly higher in pregnancies with velamentous and marginal cord insertions compared to those with normal cord insertion (24.5%, 15.2% vs 7.5%, P<0.001 and P=0.020, respectively). In pregnancies with birthweight discordance of 25% or more, the smaller twins had significantly higher prevalence of velamentous (13.8%) and marginal (34.2%) cord insertions compared to the larger twins (1.8% and 18.5%, respectively P<0.001). The smaller twins of the MCDA pregnancies showed an even higher prevalence of velamentous (29.5%) and marginal cord insertions (40.9%) compared to the larger twins (2.3% and 29.5%, respectively P<0.001). Compared to the normal cord insertion group, only velamentous insertion was significantly associated with the risk of sFGR (OR 9.24; 95% CI 2.05-58.84, P<0.001), birthweight discordance of 20% or more (OR 4.34; 95% CI 1.36-14.61, P=0.006) and 25% or more (OR 6.81; 95% CI 1.67-34.12, P=0.003) in monochorionic twin pregnancies. There was no significant association between velamentous cord insertion and TTTS (p=0.265). There was no significant association between marginal cord insertion and the development of sFGR (P=0.233), birthweight discordance of 25% or more (P=0.114) or TTTS (P=0.487). Subgroup analysis of dichorionic twins showed that abnormal cord insertion was not associated with the risk of birthweight discordance (P=0.250), sFGR (P=0.308), composite neonatal adverse outcome (P=0.637) or intrauterine death (P=0.349). CONCLUSION: Monochorionic twins with velamentous cord insertion are at increased risk of birthweight discordance and sFGR. Sonographic delineation of the placental cord insertion could be of value in the antenatal stratification of twin pregnancies. Prospective studies are required to assess the value and the predictive accuracy of this potential screening marker.