If a bride is niddah at her wedding, the ceremony is valid but certain problems arise. First, of course, the couple may not consummate the marriage until she is able to immerse in the mikveh, and they must observe all the restrictions (harchakot) concerning not touching, etc., applicable to a regular niddah. Moreover, the newlyweds may not even be left alone together, particularly at night. Although a husband and wife may be alone together when the wife is niddah, this is not the case when they have never yet had relations, because it is harder for them to withstand temptation.
The need to observe harchakot also leads to some minor changes to the wedding ceremony. To avoid embarrassment, these are done discreetly, so that only a few participants are aware of the situation.
Clearly, it is best to avoid a chupat niddah, and it is usually possible to do so through careful scheduling or with the help of hormonal treatments (see Setting the Wedding Date). With the best of planning, however, problems sometimes arise, and a couple in these circumstances should remember that marriage is meant to last forever, and a few difficult weeks in the beginning will not overshadow a lifetime of happiness.