['To determine whether the worldwide consensus that twin pregnancy after fertility treatment represents an adverse outcome to be avoided is correct.', 'Literature search via PubMed and MEDLINE, going back to 1990.', 'Academically affiliated private fertility center.', 'Mothers and offspring in singleton and twin pregnancies.', 'None.', 'Maternal and perinatal/neonatal risks as well as cost considerations for singleton versus twin pregnancies.', 'Most risk assessments of twin pregnancies after fertility treatment have used spontaneous conceptions data, which reflect different treatment paradigms and outcome benefits from pregnancies after fertility treatments. In vitro fertilization (IVF) twins demonstrate approximately 40% lower outcome risks than spontaneous twin conceptions. Most risk assessments in the literature are calculated with pregnancy as the primary outcome, but in a fertility-treatment paradigm where patients want more than one child the statistically correct risk assessment should refer to born children as the primary reference. If published data are corrected accordingly to achieve statistical commonality of outcome (i.e., one child in singleton versus two children in twins), twin pregnancies no longer demonstrate a significantly increased risk profile and/or cost for mothers or individual offspring.'] Is twin pregnancy , contrary to consensus , a desirable outcome in infertility?