Progesterone-to-follicle index is better correlated with in vitro fertilization cycle outcome than blood progesterone level

Objective: To investigate the impact of late follicular phase progesterone (P) elevation in relation to ovarian response on cycle outcome.

Design: Cohort study. The progesterone-to-follicle index (PFI) was calculated by dividing the blood P by the number of follicles ≥14 mm. The clinical pregnancy rate was calculated against the range of PFI values and blood P levels.

Setting: In vitro fertilization unit.

Patient(s): A heterogenous population undergoing IVF with pituitary suppression and gonadotropin stimulation resulting in 3-15 follicles ≥14 mm and blood P≤10 nmol/L on hCG day and resulting in fresh embryo transfer.

Intervention(s): None.

Main outcome measure(s): Association of blood P and PFI with clinical pregnancy rate.

Result(s): Data were retrieved for 8,649 IVF cycles in normal responders. The (reverse) odd ratios for pregnancy were 1.112 (95% confidence interval [CI], 1.077-1.165) for blood P and 4.104 (95% CI, 3.188-5.284) for the PFI. Elevated P levels were associated with a lower pregnancy rate only when they reached the >93rd percentile. The PFI was inversely and linearly related to the pregnancy rate for the whole range of values.

Conclusion(s): A late increase in P level is detrimental if it is a consequence of increased P production per follicle (high PFI) but not if it is a consequence of additional follicular recruitment. The PFI enables clinicians to differentiate these conditions.