The role of velamentous cord insertion in the etiology of twin-twin transfusion syndrome.

OBJECTIVE

To evaluate the prevalence of velamentous cord insertion in twin-twin transfusion using the hypothesis that such insertions may contribute to the etiology of the condition.

METHODS

All cases of placentas referred for pathologic evaluation at the University of California at San Francisco from 1984-1992 were reviewed for the citation of diamniotic-monochorionic placentation, including the presence of velamentous cord insertions. Maternal and infant records were studied for findings consistent with twin-twin transfusion syndrome.

RESULTS

Thirty-eight cases of monochorionic-diamniotic twins were identified, 11 of which showed twin-twin transfusion syndrome. The prevalence of velamentous cord insertion in the transfusion syndrome subset was 63.6%, compared with 18.5% in those without (significant difference at P < .01). Twin-twin transfusion syndrome pregnancies with velamentous insertions were delivered at a significantly earlier gestational age; they also had fewer surviving infants and were more likely to have been treated prenatally than transfusion syndrome pregnancies without velamentous insertion, although these latter two findings were not significantly different.

CONCLUSIONS

Velamentous cord insertions are more common in twin-twin transfusion syndrome pregnancies and may contribute to the development of profound disparity in fluid volume because the membranously inserted cord can be easily compressed, reducing blood flow to one twin. Large-volume amniocentesis may reduce this compressive force on the cord insertion, thus explaining the success of this mode of intervention.