Abstract: According to most rabbinic opinions, hormonal methods are generally the halachic first choice for prescribed contraception. However, the breakthrough bleeding that can be associated with these methods can be clinically significant for this patient population, as it may render the wife niddah and prohibit any physical contact.
Discussion: Hormonal contraception is generally regarded as the first choice in the halachic system because intercourse is not affected in any way. As there is no barrier to the progression of the sperm to the uterus, there is no concern of violating the prohibition against illegitimate expulsion of semen. According to Jewish Law, the situation becomes analogous to intercourse during pregnancy, when Jewish law permits and even encourages conjugal activity despite the fact that conception cannot occur. The various forms of delivery of combination hormonal contraceptives (pills, patches, vaginal rings)  are halachically equivalent.
Women who experience any bleeding from the uterus that is not caused by injury enter the halachic status of niddah. Therefore, breakthrough and withdrawal bleeding from hormones can render a woman niddah if she experiences a flow of blood from the uterus or staining larger than a minimal size on her inner thighs or white undergarments. Even light spotting can interfere with the internal examinations (bedikot)required before the mikveh immersion needed to exit the niddah status. During niddah, couples must refrain from all forms of physical contact (not only intercourse). Therefore, any bleeding side effects of hormones  are of particular concern in this patient population.
In choosing the method of hormonal contraception (combination vs progesterone only, extended vs standard formulations, medium vs low dose), the possibility of breakthrough bleeding should be taken into account.
Implications for Patient Care: Couples will often be concerned about the possibility of breakthrough bleeding when starting hormonal contraception, even if the effects are medically negligible. When beginning such contraception, it is important for the physician to emphasize that the body needs a cycle or two to adjust to the new hormonal environment, and that bleeding is likely to decrease after a few months of use.
Women taking combination hormonal contraception may ask about the possibility of prolonging the time on the active preparation in order to decrease the frequency with which they become niddah. Although halacha prescribes specific behavior for couples during niddah, there is no halachic obligation for a woman to become niddah. Therefore, this request should be considered seriously. However, women should be cautioned that prolonged use increases chances of breakthrough bleeding and thus gradually extending a standard formulation  may be better than prescribing an extended formulation. 
Women may also ask about the possibility of occasionally prolonging use of the active pills to avoid being niddah during travel or while on vacation, and how to best handle this should be discussed.
Observant patients immerse in the mikveh at the end of each niddah status. This procedure requires that all physical barriers be removed from the body. Therefore, when prescribing either the patch or ring forms of contraception, the doctor should indicated that the ring can be removed for up to three hours and the patch for up to 24 hours without reducing their contraceptive effect.  
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 Godfrey EM, Whiteman MK, Curtis KM. Treatment of unscheduled bleeding in women using extended- or continuous-use combined hormonal contraception: a systematic review. Contraception. 2013;87(5):567-75.
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