Each case should be individualized according to the type of cancer, the treatment indicated and the time available. For example, in breast cancer, there is usually an interval of 4 to 6 weeks between surgery and the start of chemotherapy. This period of time will be perfect to complete a cycle of ovarian stimulation, and it will even be possible to make two stimulations to increase the number of oocytes to vitrify.
However, there are times when it is necessary to start treatment urgently and it is not possible to wait until menstruation to start stimulation. In these cases, it is possible to assess the start of stimulation in the luteal phase (after ovulation) and even random start stimulations have been described (at any time in the cycle) with good results.
If we do not even have that 10-12 day margin to carry out stimulation and egg retrieval, there are other options that are currently part of the research but have already led to births. These would be the in vitro maturation of oocytes or the freezing of ovarian tissue.
Anovulation of hypothalamic or pituitary cause, such as intense physical exercise, low weight, etc., could also occur. Other hormonal alterations, such as alterations in thyroid hormone (TSH) or prolactin, can cause ovulation not to occur correctly.
The advanced age, also would be a cause that in spite of having periods, in many cycles ovulations do not take place of regular form.