Multiple-birth risk associated with IVF and extended embryo culture: USA, 2001

BACKGROUND: Multiple births are associated with serious adverse infant and maternal outcomes. The objective of this study was to assess the multiple-birth risk (MBR) associated with IVF and determine whether the risk is impacted by stage of embryo development at transfer. METHODS: A population-based sample of 50 819 IVF transfers utilizing day 3 or day 5 embryos performed in the USA in 2001 on women aged 20–40 years was used to assess MBR and live-birth rate (LBR), stratified by patient age, supernumerary embryo availability, and number of embryos transferred. RESULTS: Although significantly more day 5 than day 3 transfers used ≤2 embryos (69.2 versus 27.7%), the former were not associated with decreased MBR. MBR was high when >1 embryo was transferred, irrespective of embryo development stage. LBR were generally maximized with 2 embryos transferred, and for some (day 5 transfers, patients aged 35–37 years) with one embryo. Electing to transfer a single day 5 embryo appeared efficacious for some patients: women aged 20–37 years with supernumerary embryos cryopreserved had LBR of 31.6–39.5%. CONCLUSIONS: MBR is high when ≥2 embryos are transferred. Single embryo transfer is the only way to prevent many multiple births and associated adverse health outcomes.