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BACKGROUND Approximately 18% of multiple births in the USA result from assisted reproduction technology (ART). Although many studies comparing ART and naturally conceived twins report no difference in risks for perinatal outcomes, others report slight to moderate positive or protective associations. METHODS We selected twin deliveries with and without indication of ART from Massachusetts live birth–infant death records from 1997 to 2000 linked to the US ART surveillance system. The sample was restricted to deliveries by mothers with increased socioeconomic status, private health insurance and intermediate/plus prenatal care use. Our final sample included 1446 and 2729 ART and non-ART twin deliveries, respectively. Odds ratios (OR) for associations between ART and perinatal outcomes were adjusted for maternal demographic factors, smoking, prenatal care and hospital care level. RESULTS ART twin deliveries were less likely than non-ART to be very preterm (adjusted OR 0.75; 95% confidence interval 0.58–0.97) or include a very low birthweight ( CONCLUSIONS ART treatment was not a risk factor for adverse perinatal outcome, and risks for several outcomes were somewhat lower among ART twin deliveries. Nonetheless, ART is strongly associated with twinning and twins remain a high-risk group, relative to singletons. Promoting singleton gestation in assisted conception is an important strategy for reducing adverse outcomes. [ABSTRACT FROM AUTHOR]