The purpose of this study is to evaluate whether the addition of follicular flushing to the initial aspiration during oocyte retrieval increases the number of oocytes retrieved in women undergoing ovarian stimulation.

There is an ongoing debate regarding the effectiveness of follicular flushing during oocyte retrieval. Currently published studies and metanalyses suggest that follicular flushing does not improve live birth rate, clinical pregnancy rate or the number of oocytes retrieved. However, currently published studies may be confounded by the types of needle used, aspiration pressures, number of times flushing is repeated, etc. Additionally, follicular flushing should be examined in specific patient populations according to their response to ovarian stimulation.

In the current study, each woman will have one ovary (right or left) randomly assigned to be aspirated with or without the addition of follicular flushing. This study design ensures that clinical and demographic characteristics of the couple will not affect the outcomes evaluated. The primary endpoints will be the number of oocytes retrieved per ovary assigned to each group. Secondary outcomes will be the oocyte recovery rate (oocytes retrieved per follicle aspirated) oocyte maturation rate, fertilization rate, and embryo development per ovary assigned to each group.

The study population will include three subgroups according to observed ovarian response to ovarian stimulation (poor responders, normal responders, hyper responders). Assuming a minimum clinically significant difference in oocyte yield of 1 oocyte, a sample size of twenty patients per subgroup is required to yield 80% power.

Patients aged <43 years with the presence of at least one follicles >11mm in each ovary on the day of triggering final oocyte maturation will be eligible for inclusion in the study. 60 patients (20 in each of the aforementioned subgroup) will be recruited and just prior to oocyte retrieval their left and right ovaries will be randomly allocated into flushing or the no-flushing group. In both ovaries all follicles greater than 11mm will be punctured by the same 16G double lumen needle, using the same aspiration pressure. In the flushing group, flushing will be performed up to a maximum of five times or until a cumulus oocyte complex (COC) is retrieved.

In the control group all follicles greater than 11mm will be aspirated by the same double lumen needle and no flushing will be performed.

All COCs will be grouped according to the ovary they originated from by the embryologists and their development will be recorded until Day 3 following fertilization (Number of MII oocytes, number of fertilized oocytes, number good quality Day 3 embryos).

Inclusion Criteria:

• Presence of both ovaries
• 18-43 years old
• At least one follicle >11mm present in each ovary on day of triggering final oocyte maturation.

Exclusion Criteria:

• Ovarian surgery
• Monofolicular development

Participants must have both ovaries present