Relationship between follicular volume and oocyte competence, blastocyst development and live-birth rate: optimal follicle size for oocyte retrieval.

OBJECTIVE: To analyze oocyte competence in gonadotropin-releasing hormone agonist (GnRHa) stimulation cycles with regard to maturity, fertilization and blastocyst rate, as well as clinical outcome (pregnancy and live-birth rate), in relation to follicular volume, measured by three-dimensional transvaginal sonography (3D-TVS), and follicular fluid composition. METHODS: This was a prospective single-center study conducted between June 2012 and June 2014, including 118 ovum pick-ups with subsequent embryo transfer. Ovarian stimulation was performed using the GnRHa long protocol. Of 1493 follicles aspirated individually, follicular volume was evaluated successfully in 1236 using automated 3D-TVS during oocyte retrieval. Oocyte maturity and blastocyst development were tracked according to follicular volume. Intrafollicular concentrations of estradiol, testosterone, progesterone, luteinizing hormone, follicle-stimulating hormone and granulocyte-colony stimulating factor were quantified by immunoassay. Clinical outcome, in terms of implantation rate, (clinical) pregnancy rate, miscarriage and live-birth rate (LBR), was evaluated. RESULTS: Follicles were categorized, according to their volume, into three arbitrary groups, which included 196 small (8-12 mm/0.3-0.9 mL), 772 medium (13-23 mm/1-6 mL) and 268 large (≥ 24 mm/> 6 mL) follicles. Although oocyte recovery rate was significantly lower in small follicles compared with medium and large ones (63.8% vs 76.6% and 81.3%, respectively; P < 0.001), similar fertilization rates (85.1% vs 75.3% and 81.4%, respectively) and blastocyst rates (40.5% vs 40.6% and 37.2%, respectively) per mature metaphase II oocyte were observed. A trend towards higher LBR after transfer of blastocysts derived from small (< 1 mL) follicles compared with medium (1-6 mL) or large (> 6 mL) follicles (54.5% vs 42.0%, and 41.7%, respectively) was observed. No predictive value of follicular fluid biomarkers was identified. CONCLUSIONS: Our data indicate that the optimal follicular volume for a high yield of good quality blastocysts with good potential to lead to a live birth is 13-23 mm/1-6 mL. However, oocytes derived from small follicles (8-12 mm/0.3-0.9 mL) still have the capacity for normal development and subsequent delivery of healthy children, suggesting that aspiration of these follicles should be encouraged as this would increase the total number of blastocysts retrieved per stimulation. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.