Marriage in Islam is essentially a social contract, and so long as it is contracted conforming to the stated requirements, it is deemed valid. Being free of the menstrual period is not considered one of the essential conditions of a valid marriage contract in Islam in any of the acceptable schools of jurisprudence. The contract, therefore is valid—provided all of the fundamental prerequisites of a valid marriage contract have been fulfilled.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto,Ontario, Canada, states: It is perfectly all right to contract marriage with a woman while she is menstruating. There is nothing in the authentic sources of Islam or fiqh to declare such a marriage as invalid.

Since freedom from menses is not considered one of the essential conditions or integrals of a valid marriage contract in Islam in any of the acceptable schools of jurisprudence, the nikah shall be considered valid—provided all of the fundamental prerequisites of a valid marriage contract have been fulfilled. The requirements are the following: free consent of the parties to the marriage (both male and female); consent of the woman’s guardian, especially if the woman has never been married before; expression of consent; presence of two witnesses; and publicizing the marriage. It is also important for marriages to be legalized according to the laws of the land the couple is living in, in order to stave off disputes and quarrels that may arise. This is all the more important when we take into account that Islam teaches us to act responsibly by taking all the necessary steps in order to protect our own rights as well as the rights of others.

Having said this, however, I must rush to add this: Although nikah of a woman is perfectly valid during her period, consummation of marriage involving sexual intercourse cannot take place while she is still menstruating. There is, however, no taboo on all other forms of intimacy or gratifications from each other for the marriage partners during menses, although intercourse itself must be delayed until such time that menstruation has completely stopped, and she has purified herself.