A follicular volume of >0.56 cm3 at trigger is the cutoff to predict oocyte maturity: a starting point for novel volume-based triggering criteria

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ObjectiveTo determine the minimum follicular volume on the day of trigger that will correspond to a mature oocyte at egg retrieval by individualized follicular puncture and to calculate the mean follicular growth from ovulation induction to egg retrieval by SonoAVC™follicle. DesignProspective observational study of 53 women undergoing IVF, in which it was possible to identify unequivocally one or more follicles at trigger and at egg retrieval by three-dimensional ultrasound. SettingUniversity-affiliated private IVF center. PatientsThe final sample included 206 follicles from 14 oocyte donors and 39 patients. InterventionsA three-dimensional ultrasound with SonoAVC™follicle was performed at trigger and at egg retrieval. The same operator selected follicles that were easily identified on both scans and verified that they were apt to be aspirated individually. Follicles were punctured individually, recording the real aspirated volume and the maturity stage of the oocyte. Main outcome measuresThe primary outcome was the relationship between follicular volume on the day of trigger and oocyte maturity stage. The secondary outcome was the rate of follicular growth from the day of trigger to the day of oocyte retrieval as measured by SonoAVC™follicle. ResultsOn the day of trigger 206 follicles were selected. Of these, 5 could not be identified on the day of oocyte retrieval, probably due to follicular rupture (mean volume 4 cm3, range 2-7) and in 48 an oocyte was not obtained. The relationship between follicular volume and oocyte maturity was studied in 153 follicles, 125(82%) mature and 28(18%) immature. ROC curves show an area under the curve of 0.73 (95%CI:0.65-0.80, p<0.001). A follicular volume of >0.56 cm3 is the cut point with the highest Youden index having a sensitivity of 85% and a specificity of 64% to predict oocyte maturity. The mean follicular growth from trigger to egg retrieval was 26-50% in 53% of cases. ConclusionA follicular volume of >0.56 cm3 at trigger is the cut-off point with the optimal balance between sensitivity and specificity for oocyte maturity. Follicles >2-3 cm3 may undergo spontaneous rupture before egg retrieval. Given these findings, we propose new volume-based criteria for trigger: 70% of follicles >0.6 cm3 with dominant follicles between 2 and 3 cm3. These need validation by randomized controlled trials.