Consanguinity, Fertility and Reproductive Outcomes: An International Review

Consanguineous marriages have been common throughout human history, and remain so even today in many parts of the world. Many Arab countries display some of the highest rates of consanguinity and, specifically, first cousin marriages which may encompass 25 to 30 percent of all marriages. The effects of inbreeding on reproductive outcome have been extensively studied. It used to be generally believed that inbreeding contributed to increased mortality and morbidity with detrimental effects on reproductive outcome; however, some studies have shown only a moderate to slight impact. The fertility of consanguineous couples and infant and childhood morbidity and mortality in their progeny have also been extensively studied and numerous studies have concluded that consanguinity is not associated with either a significant positive or negative effect on fertility. The majority of studies found that first cousin couples produce more children. In many cases the mean number of live births to women in consanguineous marriages has been reported as being higher than that in non-consanguineous unions, although several studies found that mean fertility rates may be lower in consanguineous couples. In general, higher total fertility rates have been reported in consanguineous marriages. Reports regarding the association of consanguinity and fetal wastage are conflicting, with some reporting that the total prenatal losses were essentially the same for consanguineous and non-consanguineous. Congenital malformations have long been established to be higher in consanguineous couples about the background rate (4.5% vs 1%). Due to the principle of the existence of a common ancestor. Consanguinity is most commonly associated with inborn errors of metabolism, most of which are autosomal recessive. Consanguinity also increases the incidence of multi-factorial disorders such as diabetes, cardiovascular disorders, obesity and certain types of cancers, which may in turn affect reproductive outcomes. Pregnancy outcomes, such as increased pregnancy wastage and preterm labor have been reported with consanguineous marriages. The most significant effects on reproductive outcomes are mostly due to autosomal recessive inherited conditions and inborn errors in metabolism. In the future, with completion of the study of the whole human Genome and current advances in pre-implantation diagnosis and screening it may be possible to mitigate some of the adverse reproductive outcomes associated with consanguinity.