O-133 Follicular flushing increases the number of cumulus oocyte complexes retrieved. A Randomized Controlled Trial
Authors: Lainas G , Lainas T , Makris A , Xenariou M , Zorzovilis I , Petsas G , Kolibianakis E 
Published: June 2023

Abstract

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

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

What is known already
On the basis of published meta-analyses, follicular flushing does not seem to increase the number of COCs retrieved and the probability of pregnancy. However, eligible RCTs in these meta-analyses are characterized by significant heterogeneity regarding the population studied, the needle type and lumen diameter, the aspiration pressure and the number of flushing attempts performed. Moreover, most of the studies do not offer information regarding the flow rate of the aspiration system used. A constant flow rate has been employed in a single RCT, in which a higher number of COCs was retrieved after follicular flushing compared with single aspiration.

Study design, size, duration
This is a single-center, randomized controlled trial, performed between July and December 2022. One hundred and five patients undergoing oocyte retrieval for intracytoplasmic sperm injection, aged &lt;43 years, with BMI 18-35kg/m2 were included in the study. Random allocation of each ovary to flushing or single aspiration was performed by a study nurse on the day of oocyte retrieval, using a computer generated randomization list. Patients could enter the study only once.

Participants/materials, setting, methods
All follicles ≥11 mm were aspirated with the same double-lumen needle, using the same aspiration pressure (190 mmHg) to achieve a flow rate of 0.42 ml/sec. If no COC was found in the initial aspirate, flushing was performed in the corresponding group until a COC was retrieved, or up to a maximum of five times. The primary outcome measure was the number of COCs retrieved per ovary randomized. Values are expressed as median (interquartile range).

Main results and the role of chance
Significantly more COCs were retrieved per ovary randomized in the follicular flushing versus the single aspiration group, in all patients [5 (7) versus 2 (3), p &lt; 0.001, respectively], in patients with high [9 (3) versus 5 (4), p &lt; 0.001, respectively], normal [5 (2) versus 2 (3), p &lt; 0.001, respectively] and low [1 (1) versus 1 (1), p &lt; 0.001, respectively] ovarian response. No COCs were retrieved in 2.9% of the ovaries in the flushing group versus 16.2% of the ovaries in the single aspiration group (p &lt; 0.001).
The oocyte retrieval rate, which was defined as the ratio of COCs retrieved to the number of aspirated follicles ≥11 mm, was significantly higher in the follicular flushing versus the single aspiration group, in all patients [88.9% (25) versus 45.5% (37.5), p &lt; 0.001, respectively], as well as in patients with high [81.8% (15.1) versus 45.5% (25.0), p &lt; 0.001, respectively], normal [85.7% (28.6) versus 40% (30.0), p &lt; 0.001, respectively], and low [100% (0) versus 50% (100), p &lt; 0.001, respectively] ovarian response.
No significant differences were observed regarding maturation rate, fertilization rate and the proportion of good quality embryos on day 2 in all patients as well as in patients with high, normal and low ovarian response.

Limitations, reasons for caution
The current study design, by randomizing ovaries instead of patients, eliminates heterogeneity attributed to multiple confounders and allows a more accurate evaluation of the true effect of follicular flushing on the number of COCs retrieved. However, it does not allow the detection of its effect on the probability of pregnancy.

Wider implications of the findings
This is the first RCT to show that follicular flushing increases the number of COCs retrieved compared to single aspiration, independently of ovarian response. The data presented suggests that follicular flushing plays an important role in increasing the efficacy of oocyte retrieval.

Trial registration number
NCT 05473455