Reintroducing serum FSH measurement during ovarian stimulation for ART

What is the impact of systemic FSH concentrations during ovarian stimulation for IVF/intracytoplasmic sperm injection on systemic progesterone concentrations in the late follicular phase?

Post-hoc analysis of a previously performed randomized controlled trial (RCT) performed between November 2017 and February 2020 in a tertiary IVF centre. The RCT included patients with infertility undergoing ovarian stimulation in a gonadotrophin-releasing hormone (GnRH) antagonist protocol. The GnRH antagonist was administered at 08:00 h and recombinant FSH at 20:00 h. Ultrasound and blood tests were performed 3-5 h after the GnRH antagonist.

The subgroup analysis comprised 105 patients. Systemic FSH concentrations increased from Day 2/3 until initiation of GnRH antagonist and remained constant until the day of trigger (DoT). The total group was split according to the median FSH DoT concentration (12.95 IU/l; Group A <12.95 IU/l; Group B ≥12.95 IU/l). Significant differences, with the higher concentrations in Group B, were found for: systemic FSH concentration on Day 2/3 (P = 0.04), total gonadotrophin dosage (P = 0.03), progesterone on DoT (P = 0.001) and progesterone per follicle (P = 0.004). In the total group, systemic DoT FSH concentration was statistically significantly positively correlated with the DoT progesterone concentration and the ratio of progesterone per follicle (ρ = 0.37 and 0.38, respectively, both P < 0.001). No significant correlations were seen between the systemic DoT FSH concentration and the number of retrieved oocytes.

While ovarian response seems to be independent from the systemic FSH concentrations on the DoT, high concentrations of circulatory FSH augment the production of progesterone.