Either the natural bleeding of a miscarriage or birth or the uterine dilation and subsequent bleeding from a medical procedure such as D&C or D&E makes a woman like a niddah.
If the miscarriage occurs more than forty days after conception, and the gender of the fetus is either unknown, or was known to be a girl, the woman may immerse no earlier than the night following the fourteenth day from the passing of the fetal tissue or of the fetus, even though she theoretically could complete the process of counting her clean days earlier. (In this case, she may switch to colored underwear, and need not perform more bedikot, between finishing the clean days and immersion.)
Following IVF, the forty days are calculated from fertilization, subtracting the time period during which the embryo was frozen. So, for example, if the embryo was three days old at freezing and transferred in another cycle, the forty days are counted as the time elapsed from the day of implantation plus three.
In practice, bleeding often lasts for longer than a week. The amount of bleeding can vary widely, from the length of a heavy period to a number of weeks as after childbirth. Staining is also very common. Therefore, it is difficult to predict in advance when it will be possible to use the mikveh, and a couple should gird themselves for a long wait.
On the whole, the taharah process is the same as for any time a woman is niddah. The minimum wait begins with the onset of the niddah status. After all bleeding has ceased, she performs a hefsek taharah, counts shivah neki’im, and immerses in the mikveh. The moch dachuk is typically waived for women post miscarriage or stillbirth, and many suffice with only one bedikah per day of the shiv’ah neki’im. Other lenient measures, such as further reducing the number of bedikot, may be permitted upon halachic consultation. Bedikot should be performed gently, as the area may be sensitive.
Often, halachic guidance can help a woman reach the mikveh sooner following miscarriage. We encourage women to contact a Yoetzet Halacha or rav to discuss how best to proceed in this situation. A review of the laws of stains (see here and here) can be particularly helpful.
A miscarriage also resets a woman’s veset calendar, so she observes no more onot perishah until after her next menses. According to the view of our site’s Rabbinic Supervisors, this is the case even within forty days of conception, if a pregnancy had been medically confirmed (e.g. via a positive pregnancy test).
The couple may find the restrictions on physical affection especially challenging during the time of niddah following a miscarriage, and will need to find alternative ways to express love and emotional support. It is important for husband and wife to understand that each of them might have different reactions and needs during this time period.