Phenylketonuria and Pregnancy

Phenylketonuria and Pregnancy

If you are an expectant mother with phenylketonuria (PKU), you may be concerned about the risks the inherited disease might impose on your pregnancy and your baby. PKU is a rare disorder characterized by high levels of an amino acid called phenylalanine in the blood.

It’s important to discuss your concerns with your doctor. Your healthcare team will help you determine whether you need to take additional precautions during your pregnancy.

Can patients with PKU become pregnant?

Yes. Women with PKU can become pregnant. There is no indication that having PKU reduces the likelihood of becoming pregnant.

What are the risks of PKU to the pregnancy?

As part of pregnancy, the mother’s body undergoes many changes to support the growth of the baby and to prepare for birth.

For women with PKU who maintain their low-phenylalanine diet and keep their blood levels of the amino acid under control, there is no increased risk to the baby.

However, if expectant mothers with PKU are not controlling their diet, their babies could be exposed to high levels of phenylalanine during the pregnancy. This could cause problems with the baby’s development. These babies are more likely to be born with smaller-than-normal head size, called microcephaly, low birth weight, intellectual disabilities, and heart defects.

Can I pass PKU to my baby?

Yes, PKU is a heritable condition. If the mother has PKU and the father is a carrier, then your children will have a 1-in-2 chance of having PKU. Your children also will have a 1-in-2 chance of being carriers. If the father is not a carrier, then all of your children will be carriers. In cases in which both mother and father have PKU, then any children you have naturally also will have PKU.

What precautions should I take during pregnancy?

Your doctor may have specific recommendations for you. Every woman may have different needs during pregnancy, and there may be specific precautions that your doctor recommends for you.

It’s very important that you control your phenylalanine intake during the pregnancy. As long as your blood levels of phenylalanine stay within the normal range, the disease should not cause any problems for your baby’s development.

However, the PKU diet — which typically does not contain high-protein foods — can result in some nutritional deficiencies. Thus, it’s a good idea to discuss with your doctor whether you need to take supplements during pregnancy.

You also will need to discuss whether your medications need to change during pregnancy or after giving birth. For example, large neutral amino acid therapy blocks the entry of phenylalanine to the brain. However, it’s important to note that the therapy will not be effective in protecting your baby from high phenylalanine levels during development.

What happens after the baby is born?

Deciding whether to breastfeed or formula feed is a very personal choice. Mothers with PKU can breastfeed their child safely, as long as they maintain low blood levels of phenylalanine. If you are planning to breastfeed, it’s important to discuss with your care team whether your medications or diet need to change while you are nursing.

If your baby is underweight at birth, additional supportive care may be necessary, even for full-term pregnancies.

Like all newborns, your baby will be tested for PKU at birth as part of a newborn screening.


Last updated: July 16, 2020


Phenylketonuria News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

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