I just found out that my boyfriend's parents are first cousins. What are possible defects that could occur or be passed onto any children we might have in the future?
If examination of an extended family tree on your partner's side of the family reveals no birth defects, mental retardation, genetic disorders, chronic serious illnesses or cancer, the chances are small indeed that there would be a problem for your children. There are many other considerations as well, for example your ethnic origin, and whether it is the same as your partner. Taken alone, the simple fact of his parents being first cousins, and assuming he is healthy, would generally not be expected to increase your risks for having children with birth defects.