PKU and Pregnancy

Women with PKU have to take particular care before and during pregnancy. This is because high levels of phenylalanine (Phe) in the mother can affect the unborn baby leading to heart and brain abnormalities and many other serious problems. Fortunately, if Phe levels are well controlled during pregnancy, there is no reason why any woman with PKU should not be able to have a healthy baby.

Common Questions

We’re thinking of having a baby. What do I need to know?

It is highly recommended that all women with PKU plan their pregnancies carefully. As soon as you start thinking about having a baby you should contact your dietitian. The earlier your Phe levels are under control, the better the management for your baby’s health. You will be asked to follow a strict preconception diet and will have to regularly monitor your blood levels. 

Once your Phe levels are within the target range for pregnancy, you can start to try to conceive.  See your PKU Handbook for more information. It can take some time to adjust to the demands of a much stricter diet and levels can take several weeks to settle. Give yourself plenty of time to get used to the diet before ceasing contraception.

Do I stick to my usual PKU diet during my pregnancy?

No.  You will need to have stricter blood Phe control than normal.  Your dietitian will go through the maternal PKU diet in detail with you and work with you to help you manage the changes you need to make.

Will I pass PKU on to my baby?

PKU is a genetic condition caused by a malfunctioning gene. Our genes are inherited in pairs, with one coming from each parent.

If you have PKU, the chance that your children will also have PKU will depend on your partner. If your partner also has PKU all of your children will inherit the condition, as they will inherit one faulty PKU gene from each parent.

If your partner does not have any faulty PKU genes all of your children will inherit one PKU gene from you and will be carriers. If your partner does not have PKU the chance of having a baby with PKU is very low – from 1 in 100 to 1 in 120.


PKU Handbook [2005]. Australasian Society for Inborn Errors of Metabolism (ASIEM) (Australia and New Zealand). Chapter 1: What is PKU

PKU Handbook [2005]. Australasian Society for Inborn Errors of Metabolism (ASIEM) (Australia and New Zealand). Chapter 12: PKU and pregnancy.

Please Note: The dietary treatment for PKU varies for each person so all information presented here is for guidance only. Your own dietitian and/or doctor will advise you on all aspects relating to management of PKU for you and your family.