The high fertility in countries with a predominantly Muslim population has often been considered the outcome of religious influence, emanating from Islam's emphasis on early and universal marriage of girls and on procreation. Thus, Weeks (1988) in his study The Demography of Islamic Nations, although observing noticeable "regional and temporal" diversity in fertility among Muslim countries contends that as a group they are still in early stages of demographic transition and "the single most remarkable demographic aspect of Islamic societies is the nearly universal high level of fertility." Obermeyer (1992), on the other hand, questions the validity of this argument and maintains that "one of the problems with the Islamic explanation [of high fertility] is that it treats as monolithic, a trait that is shared by close to a billion people world-wide, and that has adapted to, and been affected by, diverse regional contexts.... the diversity in the doctrine and the cultural context of Islam calls into question the recourse to Islam as an explanation of demographic trends."
URL : http://www.lse.ac.uk/asiaResearchCentre/_files/ARCWP04-Karim.pdf