Follicular flushing increases the number of oocytes retrieved: a randomized controlled trial

Does follicular flushing increase the number of cumulus-oocyte complexes (COCs) retrieved compared to single aspiration?

Follicular flushing significantly increases the number of COCs retrieved compared to single aspiration.

On the basis of published meta-analyses, follicular flushing does not seem to increase the number of oocytes retrieved, the probability of clinical pregnancy, or that of live birth and has been associated with an increase in the duration of oocyte retrieval. It should be noted, however, that all the eligible randomized controlled trials (RCTs) in these meta-analyses have randomized patients into either single aspiration or follicular flushing. This study design might not allow the detection of the true effect of follicular flushing. Despite randomization, this might still be obscured, to an extent, by heterogeneity in patients, stimulation characteristics, and differences in the oocyte retrieval procedure.

A prospective, single centre, RCT, including 105 patients was performed between July and December 2022.

Eligible patients were those undergoing oocyte retrieval for ICSI, aged <43 years, with BMI 18-35 kg/m2. Patients with all types of ovarian response (low-normal-high), as assessed on the day of triggering final oocyte maturation, were included. Random allocation of the ovaries of each patient to either single aspiration or follicular flushing was performed on the day of oocyte retrieval, using a computer-generated randomization list. Patients could enter the study only once. All follicles from ovaries allocated to either follicular flushing or single aspiration, were aspirated by the same 16G double lumen needle, with a constant aspiration pressure of 190 mmHg, resulting in flow rate of 0.42 ml/s. In the ovaries allocated to the follicular flushing group, if a COC was not recovered in the initial aspirate of each follicle, follicular flushing was performed until a COC was retrieved, up to a maximum of five times. The primary outcome measure was the number of COCs retrieved. Secondary outcomes were oocyte recovery rate, oocyte maturation rate, fertilization rate, and rate of good quality embryos on Day 2. Values are expressed as a median (inter-quartile range).

Significantly more COCs were retrieved in the follicular flushing as compared to the single aspiration group in all patients [5 (7) vs 2 (3), P < 0.001, respectively], as well as in patients with high [9 (3) vs 5 (4), P < 0.001, respectively], normal [5 (2) vs 2 (3), P < 0.001, respectively] and low [1 (1) vs 1 (1), P < 0.001, respectively] ovarian response. In patients with low ovarian response, no COCs were retrieved in 5.7% of the ovaries in the flushing group vs 42.8% of the ovaries in the single aspiration group (P < 0.001). The oocyte retrieval rate was significantly higher in the follicular flushing vs the single aspiration group, in all patients [88.9% (25.0) vs 45.5% (37.5), P < 0.001, respectively], as well as in patients with high [81.8% (15.9) vs 45.5% (22.2), P < 0.001, respectively], normal [85.7% (28.6) vs 40.0% (30.0), P < 0.001, respectively], and low [100% (0) vs 50.0% (100), P < 0.001, respectively] ovarian response. No significant difference was observed regarding maturation rate [85.2% (30.8) vs 100% (33.3), P = 0.78], fertilization rate [76.4% (50) vs 83.3% (50) P = 0.42], and the proportion of good quality embryos on Day 2 [83.3% (40) vs 100% (50), P = 0.62]. Similarly, no differences in the above variables were observed in patients with different types of ovarian response. Follicular flushing as compared to single aspiration was associated with a significant increase in the duration of oocyte retrieval in all patients [248 s (332) vs 135 s (164), respectively], as well as in patients with high [464 s (225) vs 237 s (89), P < 0.001, respectively], normal [248 s (108) vs 141 s (95), P < 0.001, respectively], and low [64 s (59) vs 48 s (10), P < 0.001, respectively] ovarian response.

Although the current study design allows for a more accurate evaluation of the true effect of follicular flushing on the number of COCs retrieved, it does not permit the evaluation of its role on the probability of pregnancy.

This is the first RCT to suggest that follicular flushing increases the number of COCs retrieved compared to single aspiration, independently of ovarian response. This implies that follicular flushing plays an important role in the optimization of oocyte retrieval. These results, however, need to be confirmed in future studies, in which an equal flow rate should be used during oocyte retrieval.

No external funding was obtained for this study. There are no conflicts of interest to declare.

NCT05473455.

15 July 2022.

27 July 2022.