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<35 years, no prior ART cycles, ≥1 prior pregnancies, baseline follicle stimulating hormone<10 international units and ≥10 oocytes retrieved were associated with the Day 5 embryo transfer. Compared with 2001, in 2009, a broader range of candidates received the Day 5 transfer. BIAS Women undergoing multiple ART cycles over time are not linked.

CONFOUNDING FACTORS AND OTHER REASONS FOR CAUTION: We ran multivariable logistic regression to lessen the effects of the confounding factors. Cycle cancelation rates by the day of embryo transfer are unknown.

GENERALIZABILITY TO OTHER POPULATIONS: Generalizable to ART clinics included in NASS.

STUDY FUNDING/COMPETING INTERESTS: This study was funded by the Centres for Disease Control. The authors have no competing interests to declare.