The “vanishing follicle” in women with low number of developing follicles during assisted reproduction

Objective To investigate the occurrence of the “vanishing follicle” phenomenon in women with low number of developing follicles in assisted reproduction. Study design Women with ≤ 6 follicles on the day of hCG administration with ≥ 14 mm diameter were prospectively studied. Primary outcome measures were disappearance of ≥14 mm and all-diameter follicles on the day of oocyte pick-up compared to the day of hCG administration. Results Among the 120 women recruited, 95 were found eligible and completed the study. The “vanishing follicle” phenomenon occurred in 3.1% (95% confidence level: 0.7%–9.0%) and 18.9% (95% confidence level: 11.6%–28.3%) of cases affecting ≥14 mm and all-diameter follicles, respectively. In all cases, mid-late follicular serum LH and P levels remained within normal follicular phase range and trans-vaginal scan did not show signs of ovulation. Markedly, the main significant difference between the study and control groups in the ≥14 mm follicle group was serum E ₂ level on the day of hCG administration; median (Interquartile range), corresponding to 395 (382.0–405.5) versus 823.0 (544.5–1291.0) pg/mL, respectively (P = 0.04). The same trend was encountered in all-diameter vanishing follicles group but it did not reach significance. Interestingly, in all-diameter vanishing group, chronic smoking and the P/E ₂ ratio on the hCG day were significantly higher than controls. Post hoc multiple logistic regression analysis of data in accordance with the Bologna criteria reveled that antral follicle count was found to significantly affect the development of the “vanishing follicle” phenomenon. Conclusions The “vanishing follicle” phenomenon occasionally occurs in women with low number of developing follicles during assisted reproduction with no signs of ovulation. Our preliminary findings suggest that this phenomenon may be related to exhausted ovarian reserve however, an early-unrecognized LH elevation could not be ruled out.