To compare cycle outcomes after scheduling with the standard early follicular phase (EFP) versus late luteal phase (LLP) in patients undergoing GnRH antagonist cycles.

Objective To compare cycle outcomes after scheduling with the standard early follicular phase (EFP) versus late luteal phase (LLP) in patients undergoing GnRH antagonist cycles.

Design Multicentric prospective non-randomized study

Setting Two university-affiliated private assisted reproduction centers.

Patient(s) Regularly cycling women aged ≤40 years with fewer than one previous IVF attempts were enrolled. Previous low responses to controlled ovarian hyperstimulation, ovarian surgery, or polycystic ovary were exclusion criteria.

Intervention(s) Twenty patients started controlled ovarian stimulation (COS) after spontaneous menses; similarly, twenty patients started stimulation on the Friday previous to a spontaneous menses (at the end of late luteal phase), regardless of cycle day.

Main Outcome Measure(s) Primary outcome: number of mature oocytes retrieved. Secondary outcomes: fertilization rate, viable embryo rate per oocyte retrieved, cancellation rate, and clinical pregnancy outcomes from FET cycles.

Inclusion Criteria:

• Regularly cycling women aged ≤40 years with fewer than one previous IVF attempts were enrolled

Exclusion Criteria:

• Previous low responses to controlled ovarian hyperstimulation, ovarian surgery, or polycystic ovary were exclusion criteria