Follicle-stimulating hormone (FSH) plays a central role in controlled ovarian stimulation (COS) during in vitro fertilization (IVF) cycles. While baseline FSH is commonly used to assess ovarian reserve, the clinical significance of dynamic FSH changes during stimulation remains unclear. Limited evidence suggests that serum FSH levels during COS may reflect ovarian response and could be associated with follicular development and treatment outcomes, yet FSH is not routinely monitored throughout stimulation protocols.

This prospective single-center cohort study aims to evaluate the dynamics of serum FSH levels during COS and to examine their association with ovarian response and IVF outcomes. Serum FSH, luteinizing hormone (LH) and estradiol (E2) will be measured at predefined time points during stimulation. Associations between FSH levels and oocyte yield, embryo development, and pregnancy outcomes will be analyzed to better understand the clinical relevance of FSH monitoring during IVF treatment.

Background and Rationale

Follicle-stimulating hormone (FSH), secreted by the anterior pituitary gland in response to gonadotropin-releasing hormone (GnRH), plays a critical role in ovarian follicular development and estradiol production. In assisted reproductive technologies (ART), exogenous FSH is administered during controlled ovarian stimulation (COS) to promote multifollicular growth. Although baseline FSH is widely used as a marker of ovarian reserve and predictor of ovarian response, the clinical significance of dynamic FSH changes during stimulation remains insufficiently characterized.

Day 7 of stimulation represents a clinically important time point during which follicular growth and synchronization are assessed. Prior studies have suggested that serum FSH levels during COS may correlate with ovarian response and may reflect an individualized FSH threshold beyond which increasing exogenous dosing may not improve follicular recruitment. However, consensus is lacking regarding the clinical utility of serial FSH monitoring during stimulation, and it is not routinely incorporated into IVF protocols.

Understanding the relationship between FSH dynamics, follicular development, estradiol production, and treatment outcomes may support more individualized stimulation strategies and improve reproductive outcomes.

Study Design

This is a prospective observational cohort study conducted at a single academic fertility center at the McGill University Health Centre (MUHC) Reproductive Centre.

Study Population

Eligible participants include patients undergoing controlled ovarian stimulation for IVF or ICSI at the MUHC Reproductive Centre. All stimulation protocols (GnRH agonist and antagonist) and all gonadotropin formulations (including Gonal-F, Menopur, Rekovelle, and Puregon) are included.

Data Collection

Demographic and clinical data will include age, body mass index (BMI), obstetric history, indication for treatment, and stimulation protocol details.

Serum hormone levels of will be measured at three predefined time points:

1. Baseline (cycle day 3)
2. Day 7 or 8 of gonadotropin stimulation
3. Trigger day (day of trigger shot before oocyte retrieval)

Blood samples will be collected at time points that coincide with routine visits for women undergoing ovarian stimulation, during which blood tests are already performed as part of standard clinical care

The hormones measured include:

Serum Follicle-stimulating hormone (FSH) (mIU/mL) Luteinizing hormone (LH) (mIU/mL) Estradiol (E2) (pmol/L) Anti-Müllerian Hormone (AMH) (ng/mL)

Inclusion Criteria:

• Patients undergoing controlled ovarian stimulation
• All stimulation protocols (agonist and antagonist).
• All gonadotropin formulation (Gonal-F, Menopur, Rekovelle, Puregon).

Exclusion Criteria:

• Cancer fertility preservation patients .
• Patients over age 44.

Study will include patients undergoing controlled ovarian stimulation at the MUHC Reproductive Center. Nursing and medical team will recruit patients on their initial visit when they get their treatment plan and prescription at the MUHC Reproductive Center.