CFTR and cystic fibrosis: Preconception carrier screening of well‐defined deleterious mutations in the CF transmembrane conductance gene (CFTR, OMIM #602421), the only gene known to be associated with CF (OMIM #219700), is widely accepted and has been repeatedly advocated for by opinion leaders (American College of Obstetricians and Gynecologists Committee on Genetics, 2011; Castellani et al.