Trends and factors associated with the Day 5 embryo transfer, assisted reproductive technology surveillance, USA, 2001–2009

STUDY QUESTION What characteristics are associated with a Day 5 embryo transfer? SUMMARY ANSWER The use of the Day 5 embryo transfer has increased over time, with clinicians allowing women with typically ‘poorer’ prognostic characteristics to undergo a Day 5 embryo transfer. The mean number of embryos per Day 5 transfer decreased from 2001 to 2009, although the prevalence of the Day 5 single embryo transfer remains low and the rate of multiple births remains substantial. WHAT IS KNOWN AND WHAT THIS PAPER ADDS Day 5 embryo transfer may reduce the rate of multiple gestation pregnancy. US trends over time in the prevalence of the Day 5 transfer, changes in characteristics of patients receiving Day 5 transfer, and number of embryos transferred are unknown. DESIGN We used 2001–2009 US National assisted reproductive technology (ART) Surveillance System (NASS) data on 620 295 fresh IVF cycles derived from autologous oocytes with a Day 3 or 5 embryo transfer. Trends in the mean number of embryos transferred from 2001 to 2009 were assessed by the day of transfer. For 349 947 cycles from clinics performing both Days 3 and 5 embryo transfers, multivariable logistic regression was used to determine the characteristics associated with the Day 5 embryo transfer. We also compared the characteristics of the Day 5 embryo cycles in 2001 and 2009. MAIN RESULTS AND THE ROLE OF CHANCE Overall, the proportion of ART cycles using the Day 5 embryo transfer increased from 12% in 2001 to 36% in 2009 (P< 0.0001), while the mean number of embryos transferred decreased from 2.4 to 2.1 (P< 0.0001). Among Day 5 transfers, the rate of the single embryo transfer tripled from 4.5% in 2001 to 14.8% in 2009 (P< 0.0001); and the rate of multiple births decreased from 44.8 to 41.1% (P< 0.0001). In cycles initiated after 2001, maternal age