RESUMEN
OBJECTIVES: Two major complications of monochorionic diamniotic (MCDA) twin pregnancies are twin to twin transfusion syndrome (TTTS) and birthweight discordance. The current screening ultrasound test for these pathologies combines the detection of nuchal translucency discrepancy and abnormal ductus venosus in at least one twin, in the first trimester. We aim to determine whether combining the presence of velamentous cord insertion in at least one twin increases screening efficiency. METHODS: This was a retrospective cohort with a sample of 136 MCDA twin pregnancies followed at Centro Hospitalar Universitário São João, during a 16-year period. RESULTS: The combination of abnormal ductus venosus in at least one twin and nuchal translucency discrepancy is associated with the development of TTTS with an OR of 10.455, but not with birthweight discordance. The combination of these first trimester markers with velamentous cord insertion is not associated with the development of either outcome. CONCLUSIONS: The presence of velamentous cord insertion in MCDA pregnancies is not associated to TTTS development. Therefore, the addition of this marker to the first trimester screening would not effectively predict the development of birthweight discordance or TTTS. However, a positive currently used screening test increases the risk of developing TTTS by about ten times.