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Home > Vitafriendspku > Your pku journey > Pregnancy - The Facts

Pregnancy - The Facts


It is important for you to know about pregnancy if you are a female with PKU. This is because when pregnant, the amino acid phenylalanine (phe) crosses from the blood of the mother to the baby. Phe in the blood is concentrated as it passes from the mother to the baby.

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High phe levels during pregnancy can affect the normal development of the unborn baby and 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.

You can have healthy babies but to protect the baby from being exposed to very high phe, the low protein diet needs to be followed closely before starting to try for a baby and throughout pregnancy.

When the low protein diet is followed, you 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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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. This means that the low protein diet needs to be stricter, with fewer grams of protein consumed and ensuring regular protein substitute intake 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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In hyperphenylalaninemia (sometimes called “hyperphe” or “mild PKU”) the phe levels are above normal but not as high as in classical PKU, however, phe levels might still be too high than recommended for pregnancy.

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This means that the low protein diet and a protein substitute will be required for you during preconception and pregnancy.

The low protein diet is personal to you. Your metabolic team will be able to tell you more about how much your diet will need to change for pregnancy.

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Unplanned Pregnancy

If you find out you are pregnant and this was unplanned you must ring your metabolic centre as soon as you can and let them know you think or know you are pregnant.

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Your dietitian and metabolic team will:

  1. Advise you how to bring your phe level down as fast as possible by:
  • Taking the correct amount of protein substitutes every day.
  • Eating as little protein as possible.
  • Eating plenty of low protein prescribed foods for energy.
  1. Book an appointment for you to see them
  2. 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.

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Information About Contraception and Family Planning
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  • 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.


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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