I have posted this numerous times but it is always disregarded where medical issues for women’s reproductive health is concerned . Some women must use for special, serious medical conditions, medications that will damage /destroy a fetus. While on these meds, they CANNOT get pregnant.
Some birth control medications are used themselves to TREAT gynecological disorders. 
An employer has no right to an employee’s medical information and therefore cannot know why the birth control is used.
This is NOT a “one size fits all” medical issue. As a matter of fact some religious sisters themselves might have need of these medications for their own medical illnesses.