OBJECTIVE

To study the correlation between the lag time from ovulation trigger to oocyte aspiration and the proportion of metaphase II (MII) mature oocytes aspirated.

DESIGN

Retrospective study.

SETTING

Fertility and IVF center in an academic regional hospital.

PATIENT(S): A total of 511 women undergoing IVF-intracytoplasmic sperm injection at our center, with at least one oocyte available for maturity determination.

INTERVENTION(S): Data were retrieved from patient electronic databases and files. Demographic data, hormone treatments and ovarian response, and the time of ovulation trigger and oocyte aspiration were recorded.

MAIN OUTCOME MEASURE(S): The primary outcome was the proportion of MII mature oocytes relative to the total number of oocytes aspirated and allocated to intracytoplasmic sperm injection. Pregnancy rates and clinical pregnancy rates were secondary outcomes.

RESULT(S): There were fewer MII mature oocytes when the lag time between oocyte trigger and aspiration was between 33.45 hours and 34.45 hours. The proportion of MII oocytes seems to increase up to a 35-hour lag time and then stabilizes up to 38 hours. Pregnancy and clinical pregnancy rates did not differ among the different time groups studied.

CONCLUSION(S): Oocyte aspiration should be scheduled at least 35 hours after ovulation trigger. Oocytes can be aspirated in a 3-hour window of time between 35 and 38 hours without compromising results. Further research should elucidate whether even longer lag times will improve the proportion of MII mature oocytes.