Background The free androgen index (FAI) calculated using total testosterone measured by immunoassay does not correlate with oocyte fertilization rates; however, there is considerable cross-reactivity for testosterone with other androgens by immunoassay that is not found using isotope dilution liquid chromatography–tandem mass spectrometry (LC/MS/MS).

Aims This study was done to determine relationship between total testosterone and androstenedione measured by LC/MS/MS and fertilization rates.

Study design 49 infertile women without polycystic ovary syndrome were recruited preceding an in vitro fertilization (IVF) cycle. Serum testosterone and androstenedione were measured by LC/MS/MS and correlated with IVF parameters non-insulin resistant compared with insulin resistant (homeostatic model assessment >2.5) women.

Results For non-insulin resistant women, total testosterone FAI and androstenedione did not correlate with oocyte fertilization rates. In insulin-resistant women, there was a negative correlation between both testosterone and FAI and fertilization rates (r=−0.62, p<0.03) and r=−0.73, p=0.02, respectively). There was a positive correlation between androstenedione and fertilization rates (r=0.87, p<0.01).

Conclusion For insulin-resistant women, increases in testosterone and FAI were associated with reduced fertilization rates and androstenedione was associated with increased fertilization rates when measured by LC/MS/MS that should be considered to be the measurement method of choice.