The Role of Follicular Flushing at Oocyte Retrieval

In vitro fertilization (IVF) is the most commonly applied method of medically assisted reproduction and concerns the fertilization of the egg by the sperm in a laboratory environment. The process includes the following stages: Ovarian stimulation, oocyte retrieval, fertilization and culture in the laboratory, and finally, embryo transfer.

Achieving pregnancy and live birth depends on several factors. The most important is the woman's age, as the advanced female reproductive age reduces the ovarian reserve and increases the chromosomal abnormalities of the remaining oocytes. The other important factor is the number of oocytes retrieved.

Follicular flushing aims to increase the number of mature oocytes retrieved at oocyte retrieval. The present thesis investigates the role of follicular flushing at oocyte retrieval.

The randomized study will be conducted in women undergoing ovarian stimulation with recombinant follicle-stimulating hormone (recFSH) and suppression of the premature rise of luteinizing hormone (LH) using a gonadotropin-releasing hormone (GnRH) antagonist or Progestin Primed Ovarian Stimulation (PPOS). Induction of final oocyte maturation will be done with recombinant human chorionic gonadotropin (rec hCG) or an agonist of GnRH.

Women with at least one follicle of a mean diameter of 11 millimetres or more in each ovary will be eligible to participate in the studies.

On the day of oocyte retrieval, one ovary will be randomized to undergo follicular flushing using a single-lumen needle and the other simple aspiration, using the same needle. All fertilized oocytes from both ovaries will be cultured, seperately, to the blastocyst stage.

The outcomes are the number of oocytes and mature oocytes retrieved during oocyte retrieval, the oocyte retrieval rate, the mature oocyte retrieval rate, the maturation rate, the number of fertilized oocytes, the fertilisation rate, the number of blastocytes and the blastulation rate.

This study requires 75 patients (25 per response category: poor, normal, high responders) to rigorously evaluate whether follicular flushing with single-lumen needles produces clinically meaningful improvements in oocyte yield. We employed multiple conservative assumptions to ensure adequate power even under pessimistic scenarios.

Sample size was calculated for a mixed-design ANOVA testing the Response × Technique interaction. Our published pilot study (Lainas et al., HR, 2023, N=105) using double-lumen needles demonstrated large effects, but we conservatively assume single-lumen needles will show only 50-70% of these effects. We further assumed: (1) within-ovary correlations of ρ=0.35 (lower than pilot's 0.44-0.59), (2) standard deviations 20% higher than pilot data, and (3) 90% power requirement (vs. standard 80%).

Under these ultra-conservative assumptions (50% of pilot effects), n=25 per group provides 82% power. For more realistic scenarios (70-80% of pilot effects), power exceeds 90-98%. This sample size accommodates 5% attrition (target enrollment N=79), which is appropriate for within-ovary designs where dropout is minimal. The conservative approach ensures the study can detect meaningful clinical differences while satisfying rigorous peer review standards and protecting against optimistic assumptions about equipment transition.

Inclusion criteria

• Ovarian stimulation with recFSH and GnRH antagonist or PPOS protocol
• Triggering final oocyte maturation with hCG or GnRH agonist
• The day of oocyte retrieval at least one follicle of mean diameter of 11mm in each ovary
• ICSI method of fertilisation.

Exclusion criteria

• Presence of ovarian cyst of endometriosis
• History of ovarian surgery
• Monofollicular growth
• Presence of only one ovary
• Ovary not accessible at oocyte retrieval