"birth control pills start releasing early in the female cycle (+/- day 9) which stops the release of lh from the anterior pituitary. the inhibition of lh around day 15 stops ovulation.

The birth control pills start releasing progesterone hormone early in the female cycle (+/- day 9) which stops the release of the leutinising hormone from the anterior pituitary. the inhibition of the lh around day 15 stops ovulation. the mini pills work by thickening the cervical mucus so the sperm cannot reach the egg. the hormone in the pills also changes the lining of the uterus, therefore the implantation of the fertilized egg is much less likely to occur. they may also prevent the release of an egg.

Progesterone hormone

That would be a working theory.