In the past, most women nursed their children for about two years, and nursing would almost always prevent ovulation and menstruation. Consequently, a woman could not become pregnant while nursing, and there was thus a natural gap of about two years between birth and the next pregnancy. Today, reality has changed in two ways. First, the average time spent nursing has been shortened to six months or less. There are several reasons for this: women have joined the workforce, life is more stressful, and substitutes for breast milk are available. Second, for many women, nursing does not prevent ovulation and menstruation, so they can become pregnant even while nursing.
Thus, if a couple fulfill the mitzva of ona at its set times, many women would conceive a few months after giving birth, especially women who are not nursing at all or are nursing some of the time and supplementing with formula. The question arises: may a couple use contraception in the year following birth, to enable them to fulfill the mitzva of ona while avoiding another pregnancy?
Some rabbis are inclined to rule stringently and do not permit birth control except if there is a great need, such as when the mother is extremely weak or very stressed. In their opinion, the mitzva of procreation requires having as many children as possible. However, the halakha follows the opinion of most poskim, who maintain that when necessary it is permissible to prevent pregnancy using halakhically acceptable methods (as explained in sections 17-19). Experience shows that from the perspective of physical and psychological health, it is best for most women to take a break of approximately nine months to a year between birth and the next pregnancy. Accordingly, it is permissible le-khatḥila for all women to use contraceptive methods during this time. Similarly, after a miscarriage, birth control may be used for several months if necessary, based on the instruction of a God-fearing doctor.