Joanna Grossman. “Should the law be kinder to ‘kissin’ cousins?”. Find Law. April 8, 2002 – The problem comes in another component of the constitutional analysis – the “narrow tailoring” requirement, which tests the closeness of the relationship between the state’s chosen means and its desired ends. According to the recent report, children of unrelated parents have a 3 to 4 percent chance of being born with a serious birth defect. Children of first cousins have only a slighter higher risk–roughly a 4 to 7 percent chance. Thus the ban on cousin marriages will not go very far toward the general problem of preventing birth defects.