Table 2 Main characteristics of the important studies correlating follicular size and several IVF success parameters
Study/design | Patients | Stimulation protocol | Study groups | Criteria used for triggering ovulation | Statistically significant results (p < 0.05) |
|---|---|---|---|---|---|
Mohr-Sasson et al. [32] Prospective | 640 follicles measured from 204 women | Antagonist protocol | follicles were measured and divided into three groups according to their maximal dimensional size: large: ≥ 16 mm, medium: 15 to 13 mm, and small: < 13 mm | When at least two leading follicles measuring > 17 mm for maximal diameter | Follicles > 13 mm revealed a higher oocyte recovery rate and higher maturity ratio compared to smaller follicles (no diff. between medium and large follicles) |
Abbara et al. [33] Retrospective | 499 IVF cycles | Antagonist protocol | All follicles > 8 mm were measured, and combinations of follicle sizes were calculated, e.g., number of follicles 8, 8–9, 8–10, 8–11 | When two to three follicles reached 17–18 mm in diameter. Trigger was accomplished via either hCG, agonist or kisspeptin | Follicles 12–19 mm on the day of trigger contributed the most to the number of oocytes and mature oocytes retrieved |
Hu et al. [10] Retrospective | 492 IVF/ICSI cycles | Antagonist protocol | 3 groups according to their ≥ 17 mm/ ≥ 10 mm follicles ratio on the day of HCG administration (Low proportion ≤ 30%, Middle proportion 30–60%, High proportion: ≥ 60%) | When at least 3 mature follicles measuring > 17 mm | The number of oocytes retrieved in low proportion group is more than in the other 2 groups. IR, CPR, and LBR in the high proportion group were the highest among the 3 groups |
Orvieto et al. (2020) [34] Retrospective | 428 follicles measured from 204 women | Antagonist protocol | large: ≥ 24 mm and normal: < 24 mm | When at least two leading follicles measuring > 17 mm for maximal diameter | Non-significant lower oocyte retrieved in the large follicles group. No in-between group differences in MII, fertilization, and TQE rates. Nevertheless, once a zygote (2PN) was achieved, a trend toward a higher TQE rate/2PN was found in the large follicle group |
Knopman et al. [35] Retrospective | 1577 IVF cycles | Luteal GnRH agonist, antagonist or microdose agonist protocols | Based on the mean diameter of the two largest follicles on the day of trigger: < 18 mm, 18–18.9 mm, 19–19.9 mm, ≥ 20 mm | 10,000 units of IM hCG were administered when at least two lead follicles measured 17 mm in diameter | There were no significant differences noted for cycle parameters or outcomes for the 4 groups. However, although LBR was not significantly different, there was a decline noted as lead follicle size increased |
Knopman et al. [35] Retrospective | 360 follicles measured from 49 IVF/ICSI cycles | Long agonist, flare or antagonist protocols | Group A (mean diameter 12–14.5 mm), group B (mean diameter 15–18 mm) and group C (diameter > 18.5 mm) | When at least two follicles had mean diameters of 20 mm | Significantly higher oocyte recovery rate from large compared to small follicles. In addition, the aspiration of follicles greater than 18 mm. provided the highest probability of retrieving mature oocytes (MII) |
Dubey et al. [30] Retrospective | 2,429 oocytes from 215 patients undergoing 324 stimulated IVF cycles | Long agonist protocol | Large follicles ≥ 16 mm and small follicles ≤ 14 mm | When at least two follicles had a mean diameter of 20 mm, or the E2 level approximated 250 pg/ mL per follicle | Small size follicles are still capable of containing mature oocytes, but their rate of abnormal or no fertilization is high |
Ectors et al. [31] Prospective | 412 IVF/ICSI cycles from 340 women | Long agonist protocol | Follicles were measured and divided into three groups according to their maximal dimensional size: large: > 23 mm, medium: 16 to 23 mm, and small: < 16 mm | when most large follicles reached 18–20-mm diameter and when serum oestradiol concentration per Introduction developed follicle was ~ 1100 pmol/l | The fertilization rate of all oocytes regardless of morphological type revealed a positive linear correlation with increasing follicle diameter |
Das et al. (2013) [36] Retrospective | 114 women | Antagonist protocol | According to the leading follicle diameter on the day of trigger: group 1:17–18 mm, group 2: 19–20 mm, group 3: > 20 mm | When ≥ 3 follicles were ≥ 17 mm in diameter | Oocytes from follicles with a mean diameter ≥ 16 mm had significantly higher fertilization rates than did oocytes from follicles with a mean diameter ≤ 14 mm |