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Home > Vitafriendspku > Your pku journey > Planning A Pregnancy And Pre-Conception

Planning A Pregnancy And Pre-Conception

Planning a Pregnancy

In addition to the recommendations for all females who are planning to become pregnant, eg...

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  • eating a healthy diet,
  • taking folic acid supplements,
  • being a healthy weight,
  • stopping smoking, avoiding alcohol and
  • seeking support for existing medical and mental health problems if required.

You also need to follow a strict low phe diet both before becoming pregnant and during pregnancy.

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Following the Low Protein Diet Before Getting Pregnant

The best outcomes of pregnancy are seen with mothers who have their blood phe under control prior to becoming pregnant and in the early stages of pregnancy.

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Having phe levels controlled before pregnancy means your baby is protected right from the start. The heart and brain start developing soon after conception. Keeping the phe levels controlled in the early weeks of pregnancy is important to protect the baby’s heart and brain as they start to form.


You may not know you are pregnant until you miss your first or second menstruation which relates to the 4th or 8th week of pregnancy.

At 6 weeks the heart may be beating, and the brain and spinal cord are developing. The foetus will be the size of a pea.

At 8 weeks the limb buds are developing, and the foetus will be the size of a kidney bean.

By 12 weeks the organs of the foetus including the brain are formed. The foetus will be the size of a lemon.

When the low protein diet is followed, you are just as able to have healthy babies as women without PKU.

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When to Start the Low Protein Diet When Planning For a Baby

The low protein diet should be started and the phe levels should be in the lower target range for pregnancy before trying to conceive a baby (before trying to get pregnant), this is known as a “planned pregnancy”.

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Most metabolic centres ask to be told about 6 months before you want to start trying for a baby, therefore a reliable form of contraception should be used. This is to make sure they can organise for extra dietary training and support, set up the supply of low protein foods and protein substitute, and help you make the necessary changes to your diet to reduce the blood phe into the target range for preconception and pregnancy.

Blood phe levels should be stable in the target range for preconception and pregnancy for 2-3 months before it is safe to stop contraception. Each person is different, and your dietitian can tell you more about what this might be like for you.

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Why the Diet is Important
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The low protein diet together with the protein substitute lowers the blood phe and provides all the nutrients you and your baby need to be healthy.

Protein substitutes provide protein without the phe (or are very low in phe). Taking enough protein substitute with vitamins and minerals during pregnancy provides your baby with the right nutrients to grow. Nutrients like protein, iron, vitamin B₁₂, essential fatty acids (DHA) and folic acid are important for the baby’s growth and the development of their heart and brain. Your dietitian will recommend how much protein substitute and any extra supplements that are needed. It’s important to take the full amount that your dietitian recommends to get everything that you and the baby need.

Speak to Your Dietitian and Try the Protein Substitutes Available For You:

  • There are lots of different options available: ready-to-drink pouches, powder in sachets, powder in tins, or tablets.
  • Different types might suit your lifestyle better e.g. light-weight sachet might be easier to carry around in your handbag or a ready-to-drink option might be easier to take on the go.
  • Taste changes are common in pregnancy so it’s important to know which options you might like to swap to if needed.
  • You can mix and match to have different types and flavours.
  • You might find that a neutral option, where you can add your own preferred permitted flavours may be useful.

Always check with your dietitian before you make any changes to your protein substitute.

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What Should I Do if I Struggle to Take My Protein Substitute?
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Essential tips to make taking your protein substitute a success:

  1. Take every drop- drink all your protein substitute to make sure you get all the nutrients.
  2. Shake it up: give your protein substitute a good shake before drinking.
  3. Drink afterwards – after taking your protein substitute drink a glass of water or permitted drink to reduce any chance of stomach discomfort.
  4. Try it cold – people say their protein substitute doesn’t taste as strong if it’s really cold.
  5. Make a paste or “shot” – some can be made into a really small drink or paste to take it in one or two mouthfuls.
  6. Take it with food – take your protein substitute after a meal or with a small snack to help reduce any chance of stomach discomfort.
  7. Remember to take it – set a reminder on your phone, put a note on your mirror, keep a small supply in your handbag and at work / college so you always have some handy.

Speak to your metabolic team if you are still struggling to take all your protein substitute.

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Specially Manufactured Low Protein Foods
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Specially manufactured ow protein foods are especially important during preconception and early pregnancy when your intake of natural protein is likely to be very limited. Low protein foods provide important energy, that keep you full and provide variety.

  • There are lots of options of low protein foods available such as bread, cereal, pasta, flour and egg replacers, milk alternatives, snacks, biscuits, cakes, chocolate and many more! Say yes to any free samples you are offered so you can have as much choice and variety as possible.
  • There are lots of low protein recipes available and more are being developed all the time. During preconception it is ideal to try out a few different recipes to find the ones you like before you get pregnant. Why not find a low protein alternative to your favourite meal and test it out?
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Useful Resources for Recipes:
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  • There is a Recipe booklet which includes recipes specifically for preconception and pregnancy.
  • Live low protein cookery demonstrations are organised throughout the year all over the UK. Why not sign-up to VitafriendsPKU newsletter, or follow VitafriendsPKU on Instagram or twitter and see if you can go along to the next one? To sign up, click here.
  • Lots of delicious low protein recipes are available here.
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Learn more about PKU

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