women with pku who are pregnant or trying to get pregnant have to be especially careful to follow this diet. if they do not follow the diet, their babies could be born with severe birth defects and mental retardation. babies born to women with pku who have followed the pku diet throughout their pregnancy are usually healthy and do not necessarily but may develop pku. whether or not they have pku themselves depends on the mother and father's genes. in fact there are people who are carriers (dormant genes) that can be passed on until they resurface in the future generations. these are so far undetectable, however, since pku is genetically recessive it takes pku genes from both parents to cause pku.