In April 2002, the Journal of Genetic Counseling released a report authored by a team of scientists led by Robin L. Bennett, a genetic counselor at the University of Washington and the president of the National Society of Genetic Counselors, which showed that the potential risk of birth defects in a child born of first cousins was slightly higher than the risk associated with a non-cousin couple. The report estimated the increased risk for first cousins at 1.7 - 2.8 % over the base risk of about 3%, or about the same as that of any woman over age 40, or of a still younger man (see paternal age). Put differently, first-cousin marriages entail roughly the same increased risk of birth defects as a woman faces when she gives birth at age 41 (roughly 6%) rather than at 30 (roughly 3%). Critics argue that banning first-cousin marriages would make as much sense as trying to ban childbearing by older women. These numbers were reported only for first instances of cousin mating; repeated generations of cousin coupling are thought to increase the risk substantially.
