Significance of placental cord insertion site in twin pregnancy.

OBJECTIVE: To investigate the association between abnormal cord insertion and the development of twin-specific complications, including birth-weight discordance, selective fetal growth restriction (sFGR) and twin-to-twin transfusion syndrome (TTTS).

METHODS: This was a single center retrospective cohort study of twin pregnancies. Abnormal cord insertion was defined as either marginal (umbilical cord attachment site less than 2 cm to the nearest margin of the placental disc) or velamentous (cord 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. Twins with major structural or chromosomal abnormalities and monochorionic monoamniotic twins were not included in the study. Information on the pregnancies, ultrasound findings, prenatal investigations and interventions was obtained from the electronic ultrasound database, while data on placental histopathological findings, pregnancy outcome, mode of delivery, birth weight, gestational age at delivery and admission to the neonatal intensive care unit were obtained from maternity records. Categorical variables were compared using the chi-square or Fisher's exact test, while continuous variables were compared using the Student's t-test, ANOVA for multiple comparisons and the Kruskal-Wallis test.

RESULTS: Of the 497 twin pregnancies included in the analysis, 351 (70.6%) were dichorionic and 146 (29.4%) were monochorionic. The incidence of birth-weight discordance of 25% or more was significantly higher in pregnancies with velamentous and those with marginal cord insertions compared to those with normal cord insertion (24.0%, 15.3% vs 7.6%, P < 0.001 and P = 0.020, respectively). In pregnancies with birth-weight discordance of 25% or more, the smaller twins had significantly higher prevalence of velamentous (13.8%) and marginal (34.2%) cord insertions compared with the larger twins (1.8% and 18.5%, respectively, P < 0.001). The smaller twins of the monochorionic diamniotic pregnancies showed an even higher prevalence of velamentous (29.5%) and marginal (40.9%) cord insertions compared with the larger twins (2.3% and 31.5%, respectively, P < 0.001). Compared with the normal cord insertion group, only velamentous insertion was associated significantly with the risk of sFGR (odds ratio (OR), 9.24 (95% CI, 2.05-58.84), P < 0.001) and birth-weight discordance of 20% or more (OR, 4.34 (95% CI, 1.36-14.61), P = 0.007) 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 = 0.591), or between marginal cord insertion and the development of sFGR (P = 0.233), birth-weight 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 birth-weight discordance (P = 0.999), 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 birth-weight discordance and sFGR. Sonographic delineation of placental cord insertion could be of value in the antenatal stratification of twin pregnancies. Prospective studies are required to assess the value and predictive accuracy of this potential screening marker. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.