Sometimes one ovary is inexplicably resistant to stimulation, but it doesn’t affect fertility too much
Unilateral ovarian response to IVF stimulation is not infrequent and can have different causes, from a missing ovary, to a vascular-compromised ovary (usually after surgery) or an ovary compromised by infiltrating endometriosis. All of these causes can lead to one-sided failure to respond or poor response to ovarian stimulation during IVF. Sometimes, it just happens without any obvious reasons.
During natural cycles, women usually release only one egg every month; moreover, ovaries usually alternate sides every month from where they release. What regulates this process is not clear, but it is surprisingly consistent into advanced ages: as long as women spontaneously ovulate, they do so from usually alternating ovaries in sequential months. If one ovary is removed, the other one knows to compensate and immediately goes from every other to every month schedule.
When during ovarian stimulation, only one ovary responds, anatomic differential diagnoses outlined above becomes necessary. If none applies, and the second ovary by size and consistency looks normal on ultrasound, then one may just be a victim of a short-term block in the suddenly resistant ovary. Some experts have suggested that this may have something to do with the still unknown mechanism that regulates alternate-side ovulation. Should that be the case, then in the following months, this ovary should respond normally. If resistance to stimulation is demonstrated to be a persistent pattern, then it becomes necessary to go back with the patient to her past medical history and, more often than not, one will discover that the patient had some unmentioned ovarian surgery or, maybe, an ovarian torsion at younger years.
Not much can be done then in such cases. In some instances, administration of vasodilators will help by dilating a compromised vasculature, allowing the ovary to regain some blood flow and improve responsiveness. In most cases, however, a “dead” ovary remains “dead,” even with treatments.
On a side note, in both human clinical experience and experimental animal models, removal of one ovary affects fertility only to rather minor degrees. Having one unresponsive ovary, therefore, should not affect a woman’s fertility very much, as long as her second ovary still behaves normally.