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Home > Vitafriendspku > Your pku journey > PKU and Pregnancy (Teens)

PKU and Pregnancy (Teens)


It is important for you to know about becoming pregnant if you are a female with PKU.

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This is because when pregnant, phe, crosses from the blood of the mother to the baby. The baby is exposed to higher phe than what is in the blood of the mother.  

High phe levels during pregnancy can affect the normal development of the unborn baby and potentially cause miscarriage.  The damage from high phe levels is permanent and can harm brain development leading to learning difficulties, microcephaly (a small head), heart defects and low birth weight. This is known as maternal PKU syndrome. 

To protect the baby from being exposed to very high phe levels the phe-restricted diet needs to be followed strictly before you start trying for a baby and throughout pregnancy. So the good news is when the low protein (low phe) diet is followed, women with PKU are just as able to have healthy babies as women without PKU. 

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The diet for pregnancy

The phe level before pregnancy (preconception) and during pregnancy needs to be lower than is advised for teenagers and adults.

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Normally it is recommended that phe levels are between 120 - 360umol/l for preconception and during pregnancy, although your own metabolic centre may advise on slightly different levels as you are a teenager. This means that the low protein diet needs to be stricter, with less protein and regular, sometimes more protein substitute to keep the phe levels low and stable.  

Your metabolic dietitian will be able to tailor the diet to your needs. 

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Will my child inherit PKU?

Your child can only inherit PKU if the father is a carrier of a PKU gene.

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The chance of being a carrier for PKU in Australia is 1 in 50, making the chance of your child inheriting PKU approximately 1 in 100. If the father is not a carrier, the baby will not have PKU. 

If you have any further questions speak to your metabolic team. 

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Unplanned pregnancy

If you become pregnant and this was unplanned, you must ring your metabolic centre immediately and let them know. 

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Your dietitian and metabolic team will:

• Advise you how to bring your phe levels down as quickly as possible by:

  • Taking the correct amount of protein substitute every day.
  • Eating as little protein as possible
  • Eating plenty of low protein prescribed foods for energy

• Book an appointment for you to see them

• Ensure early contact with your GP/Midwife so an appropriate referral to an obstetric /gynaecology service can be made.


Reducing phe levels quickly decreases the time the baby is exposed to high phe levels and limits the chance of damage. If the low protein diet is started early in pregnancy and the phe levels are reduced quickly into the target range by 10 weeks of pregnancy, the baby can still be healthy.  

It can be more challenging to get phe levels under control if starting the diet once pregnant. Keeping in regular contact with your metabolic dietitian and sending blood spot cards as advised will help you achieve target levels. 

If you would like any further information regarding contraception or planning for a baby, please see below: 

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Information about contraception and family planning

• GP Surgery/Practice Nurse

• Local Sexual Health or Family Planning Clinic

Family Planning Alliance Australia

Health Direct: select Family Planning for information on contraception or getting pregnant

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Family Planning- state based websites


You can get contraception from the following places 

  • GP Surgery/Practice Nurse 
  • Local Sexual Health or Family Planning Clinic 
  • Supermarket or pharmacy 
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Learn more about PKU

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