Why Birth Control Pills (BCP) prior to IVF?

Have you wonder why BCP is usually given in the IVF long protocol?

I've done some research and found an answer there:
http://100infertilityquestions.blogspot.com/2008/01/birth-control-pills-and-ivf-protocols.html

First, in patients who are known or suspected to be high responders, OCPs may help mitigate the risk of ovarian hyperstimulation syndrome

Second, in patients without predictable regular menstrual cycles, OCPs can be used in combination with Lupron to initiate an IVF cycle.

Third, some clinics use OCPs for microdose Lupron (MDL) flare, traditional flare, or patients who are taking Antagon in the hope that pretreatment with OCPs will prevent one follicle from growing faster than the other follicles once the stimulation has begun.

Given that prolonged OCP use can lead to oversuppression in low responders, it has to be used very carefully.