OBJECTIVE: To investigate whether diamniotic twin gestations are at increased risk of amniocentesis-related adverse outcomes compared to singleton pregnancies.STUDY DESIGN: This was a retrospective study of mid-trimester amniocenteses performed during the period 1993-2009. Cases were divided in two groups, one including singleton (Group 1) and the other diamniotic twin pregnancies (Group 2). All amniocentesis-related adverse outcomes were reviewed, including aspiration of insufficient amniotic fluid, aspiration of hemorrhagic amniotic fluid, repeated puncture and miscarriage. The incidence of these adverse outcomes was compared between the two groups.RESULTS: In total, 6270 cases were included in the study (Group 1, n=6150 and Group 2, n=120). Advanced maternal age was the main indication for amniocentesis in both singleton and twin pregnancies. There was no difference in the incidence of insufficient sample aspiration (0.2% in singletons vs. 0.0% in twins, P=NS), in the incidence of blood-stained amniotic fluid (3.7% in singletons vs. 4.6% in twins, P=NS), in the rate of need for second attempt (2.1% in singletons vs. 1.7% in twins, P=NS) or in the miscarriage rate (0.24% in singletons vs. 0% in twins).CONCLUSION: In our experience, the incidence of amniocentesis-related adverse outcomes is not increased in diamniotic twins compared to singleton pregnancies.