Objective: To examine the independent contribution of abnormal flow in the ductus venosus at 11 to 13 weeks of gestation in the prediction of adverse pregnancy outcome in relation to chorionicity.
Methods: This was a prospective study in 516 dichorionic and 179 monochorionic twin pregnancies in which the fetal ductus venosus flow was assessed at 11 0/7 to 13 6/7 weeks of gestation. The prevalence of reversed a-wave in the fetal ductus venosus was compared between monochorionic and dichorionic pregnancies and between those with and without pregnancy complications. Comparisons between each of the pregnancy outcomes and the normal outcome group and between monochorionic and dichorionic pregnancies were made using the Mann-Whitney U-test for continuous variables and the chi2 test and Fisher exact test for categorical variables.
Results: The prevalence of reversed a-wave in at least one of the fetuses was significantly higher in monochorionic than in dichorionic pregnancies (18.4% compared with 8.3%, P<.001) and in pregnancies complicated by miscarriage (28.6%, P=.005), fetal aneuploidy (70.0%, P<.001), and twin-twin transfusion syndrome (38.5%, P<.001) compared with the pregnancies with two healthy live births (7.7%). Pregnancy outcome was normal in 33 of the 43 (76.7%) dichorionic and in 14 of the 33 (42.4%) monochorionic twins with reversed a-wave in at least one of the fetuses.
Conclusion: In twins, reversed a-wave in the ductus venosus at 11 to 13 weeks of gestation is associated with increased risk for aneuploidies, miscarriage, and development of severe twin-twin transfusion syndrome. However, in about 75% of dichorionic twins and 40% of monochorionic twins with reversed a-wave, the pregnancy outcome is normal.
Level of evidence: II.