OBJECTIVE: To investigate the impact of operator experience on amniocentesis-related adverse outcomes.STUDY DESIGN: Retrospective study of mid-trimester amniocenteses performed by the same operator on singleton pregnancies in a single private institution during 1994-2007. Outcomes were hemorrhagic or dark amniotic fluid aspiration, insufficient volume aspiration, repeated puncture and fetal loss. Rates were estimated annually, as well as for every 10% of procedures up to the total number. The association of each outcome with epidemiological aspects was also examined.RESULTS: In total, 5913 amniocenteses were performed. The overall rate of adverse outcomes was 5.4%. The total adverse outcome rate reduced from 10.2% in the first 10% of cases to 3.0% in the last 10% (P=.001). The rate of hemorrhagic fluid gradually decreased from 4.4% to 1.5% (P=.05) over the same intervals. The fetal loss rate was also reduced from 0.5% during the first half to 0.3% in the second half of the study period (P=NS). Logistic regression analysis indicated no significant correlations between adverse outcomes with any of epidemiological parameters of women undergoing amniocentesis.CONCLUSION: Operator experience has a beneficial impact on preventing procedure-related adverse outcomes.