What is the most relevant standard of success in assisted reproduction? Assessing the BESST index for reproduction treatment

It has been proposed that use of performance indicators for assisted reproduction treatment (ART) should be revised to better reflect the burden of treatment endured by a couple, and to place greater emphasis on the desired outcome of healthy babies. Recently, the BESST (birth emphasizing a successful singleton at term) score as a routine measurement for use in ART has been suggested. We applied the BESST index to a sample of ART patients and found that the BESST score was sensitive to the effects of patient age and extremes in the number of embryos transferred. However, the statistical properties of the index placed great weight on the effective implantation rate, which when applied to a time series in which implantation rates were improving, showed BESST scores to increase simultaneously with multiple pregnancy rates. This limits the completeness of the summary score as an expression of benefits compared to risks. A modified BESST index, not including cycles of initiated treatment as a denominator, indicated that the ART births contained a substantially lower proportion of BESST babies when compared to the entire population of births.