In the US, about 3,000 women of childbearing age have PKU. A woman with PKU can have a healthy baby but it is very important that she stay on a special diet to control her phenylalanine intake while she is pregnant. According to MotherToBaby, babies born to mothers with untreated PKU (women who are not on the special diet) are commonly born smaller, have microcephaly (an abnormally small head), intellectual disabilities, behavior problems, facial features similar to those of fetal alcohol syndrome, and have higher risks of heart defects.
Managing PKU during pregnancy
If you have PKU and are planning to get pregnant, it is very important that you talk to your health care provider. Many people with PKU now maintain their special diets throughout life. But if you have not been following your PKU diet, it is best to return to your PKU meal plan at least 3 months before you try to get pregnant.
PKU meal plans are different for everyone because people with PKU can tolerate different amounts of phenylalanine. For this reason, it is very important that you talk to health care providers who are familiar with managing PKU during pregnancy. Blood tests throughout pregnancy can help to monitor your phenylalanine levels and make sure that they are not too high. And your prenatal care provider may order ultrasounds to monitor your baby’s growth.
Will my baby have PKU?
If you have PKU, your baby has a chance to have PKU. Your baby has to inherit a mutation for PKU from both parents to have PKU. Whether or not your baby will have PKU depends on if your partner has PKU or is a PKU carrier. (A PKU carrier has one copy of the PKU mutation but does not have PKU.)
- If you and your partner both have PKU, your baby will have PKU.
- If you have PKU and your partner is a carrier, than there is a 50% chance your baby will have PKU and a 50% chance your baby will be a PKU carrier.
- If you have PKU but your partner does not carry the gene change for PKU, then your baby will be a PKU carrier but will not have PKU.
If you are not sure if your partner is a PKU carrier, there are tests available that can help you find out. A genetic counselor can better help you understand your chances of passing PKU to your baby.
All babies born in the United States are tested for PKU through the newborn screening program. Babies born with PKU are immediately placed on a special diet that significantly reduces the amount of phenylalanine they consume. Babies who have PKU may never show symptoms if they are transitioned to a low-phenylalanine diet soon after birth.
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