OBJECTIVE: To investigate perinatal outcomes associated with fertility treatments, including assisted reproductive technology (ART), intrauterine insemination with ovulation stimulation (IUI), and ovulation stimulation alone (OS). DESIGN: Population-representative cross-sectional survey of women with live births, 2004-2008. SETTING: Florida, Maryland, and Utah, USA. SAMPLE: 21 803 women, weighted to represent 1 022 597 women. METHODS: Survey and birth certificate data were analysed with logistic regression models adjusted for age, education, race, income, and parity, using separate models for singletons and all births. We used two referent groups: (1) women who never used fertility treatment and (2) subfertile women conceiving without treatment. MAIN OUTCOME MEASURES: Preterm birth (<37 weeks), very preterm birth (<34 weeks), low birthweight (<2500 g), and very low birthweight (