Relationship between follicular volume, oocyte competence, and blastocyst development in art

Abstract

Aim: To analyze oocyte competence in assisted reproductive technology (ART) using gonadotrophin releasing hormone (GNRH) antagonist stimulation protocol with regard to maturity, fertilization, and blastocyst development in relation to follicular volume (FV), measured by three-dimensional (3D) ultrasonography (USG) using SonoAVC software. Materials and methods: This was a prospective observational single-center study conducted at our center from April 2019 to September 2019 in which 30 cases of ovum pickup were evaluated. A single cycle of in vitro fertilization (IVF) per patient was considered. A controlled ovarian stimulation was done by GNRH antagonist induction protocol. Gonadotropin dose calculation was based on the scoring system designed on the basis of parameters which included age, body mass index (BMI), and USG parameters on baseline scan which included antral follicle count, ovarian volume, stromal resistance index (RI), and stromal peak systolic velocity (PSV). Stimulation was started on day 2 of the cycle. Scans at regular interval commencing from day 5 or day 6 of the stimulation were done to track follicular and endometrial development. Multiple follicular development due to controlled ovarian hyperstimulation in ART causes growth of follicles of different sizes and functional activity that will contain oocyte at different maturation status. So, this multiple follicular development results in polygonal shape of the follicles where two-dimensional (2D) measurements are not accurate of its size. Total number of follicles and volume of each follicle were evaluated on the day of trigger using SonoAVC software by 3D USG. Oocyte retrieval was done 35 hours after trigger, and metaphase 2 (M2) oocytes, fertilization, and blastocyst development were tracked according to 3D follicular volume (FV) with the help of our embryologist. Follicles were grouped according to FV, into three arbitrary groups, which included 313 small (0.3–0.9 mL, 8–12 mm), 414 medium (1–6 mL, 13–23 mm), and 11 large (>6 mL, ≥24 mm) follicles, all of which were aspirated and evaluated. The cumulus oophorus complex (COC) recovery rate was statistically significant (p < 0.0001) in small follicles (63%) compared with medium (86.4%) and large (63.6%) follicles. However, fertilization rate did not differ when calculating the 2PN/M2 between the three follicle groups (2 pronuclear (PN)/M2: 76.9% in small, 81.9% in medium, 60% in large, p > 0.2). Additionally, blastocyst rate per retrieved M2 oocyte was observed in all three groups (36.5% vs 46.2% vs 40%), respectively, but the difference was not statistically significant. Results: Our data indicate that the optimal follicular size for a high yield of good quality blastocysts 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 fertilization. Conclusion: Earlier clinical practice suggests aspiration of follicles of only 1–6 mL volume, but based on our results, aspiration of small follicles (0.3–0.9 mL/8–12 mm) should be a routine procedure, which would help for better oocyte yield and blastocyst rate.