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PKU and Pregnancy
What to Expect When You’re Expecting?

You are unique and your diet will be tailored for your pregnancy by your metabolic dietitian. Your diet is likely to change several times throughout your pregnancy to keep your phe levels in range.

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This will be linked to many factors including your weight before becoming pregnant, your phe tolerance, how far into your pregnancy you are, the growth of your baby and what you like to eat and drink.

Whether you were expecting to become pregnant or it was a surprise, it is important to let your metabolic team know as soon as you have a positive pregnancy test as you must follow a strict pre-conception diet. This is so they can give you the right advice for you and your baby. It is also important to make early contact with your GP/Midwife to ensure a referral to the appropriate obstetric/gynaecology service is made.

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First Trimester 0-12 Weeks
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Maintaining blood phe levels in the target range in the early weeks of pregnancy is important to protect your baby’s heart and brain as they start to form.

Dietary phe tolerance is lowest in the first trimester so your diet will likely be very restrictive. As your phe tolerance is so low, you might find small changes in your eating patterns can affect your phe level. Try to keep your dietary intake, including protein substitutes, as regular and stable as possible.

Pregnancy associated nausea and vomiting, viruses, infections and changes in appetite can make consuming enough calories or protein substitute very difficult. This can lead to high phe levels. Tips on how this can be best handled can be found below.

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Second and Third Trimester – 13 to 40 Weeks
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After approximately 16 weeks of pregnancy your phe exchanges can increase rapidly as the baby grows. Your dietitian will advise you on how to increase your dietary phe. Having low phe levels (below 100µmol/L) during pregnancy has been linked to slower growth in babies. So, it is important to follow the advice of your dietitian.

For ideas of recipes with adaptable phe exchanges, download recipe booklet here.

Getting the right nutrition throughout pregnancy is important for you and your baby. Your protein substitute (and the extra vitamins and minerals) are vital for helping to keep your phe low and providing the right nutrients for growth. Nutrients like protein, iron, iodine, vitamin B₁₂, essential fatty acids (DHA) and folic acid are important for the baby’s growth and the development of their heart and brain. It’s important to follow the recommendations from your dietitian to get the right nutrients.

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Nausea and Vomiting
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Nausea (feeling sick) and vomiting during pregnancy is normal whether you have PKU or not. It is often worse on waking in the morning but can happen at any time of day. Not all women will get morning sickness, but it is very common in early pregnancy and usually clears up by 16-20 weeks of pregnancy.

In PKU, pregnancy associated nausea and vomiting can affect your appetite and ability to take your protein substitute. If you are not managing to take your protein substitute or enough energy (calories) your phe levels will increase.

If you are feeling sick or struggling to take your protein substitute it is important to tell your metabolic team as soon as possible. Nausea and vomiting can often be managed more proactively in pregnancy and PKU. Anti-sickness medications called anti-emetics may be recommended to control the nausea and vomiting to help limit any rise in phe levels. Sometimes an admission to hospital is required to assess the condition and determine the best course of management for you and your baby and rule out any other cause for the nausea and vomiting. For example, urinary infections.

Here are some tips for dealing with nausea or sickness in a PKU pregnancy which can be followed in discussion with your dietitian:

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Managing Your Calorie Intake

Managing to balance energy (calorie) intake in pregnancy is tricky, and even more so in PKU.

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Your Metabolic Dietician Will:

  • tailor your diet to you throughout your pregnancy
  • tell you how much energy you will need from your diet
  • help you choose the right protein substitute for your needs – you might be told it would be better to choose a high or low energy option
  • monitor your phe levels regularly
  • check your weight when you attend metabolic clinic – they might also ask you to weigh yourself at home

Your weight and the baby’s growth will be checked at your appointments with your midwife or obstetric team.

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Getting Enough Energy
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If you’re feeling sick or have a poor appetite it can be difficult to get enough energy (calories). Some tips to get extra energy in a low protein diet are:

  • Use oil generously in cooking or on top of your salad and cooked vegetables
  • Add butter, mayonnaise and phe free salad dressings to salads and cooked vegetables and use generously on low protein crackers or bread
  • Avoid skipping meals
  • Snack between meals
  • Ensure you have a good range and supply of low protein prescribed foods
  • Make your protein substitute up with a protein free milk, fruit juice or high sugar, caffeine-free drinks
  • Enjoy nourishing drinks such as smoothies (make sure they are made with exchange-free fruit), low protein “milk” shakes or high sugar, caffeine-free drinks
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Controlling Energy
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Your dietitian will be able to provide tailored advice for you if you need to limit your energy intake in pregnancy. Some tips to limit extra energy for a low protein diet are:

  • Avoid sugary drinks – aim for water, soda water, mineral water, low sugar lemonade, low sugar cola varieties, fruit cordial or squash with permitted sweeteners (check the label to avoid aspartame
  • Base your meals around permitted vegetables aiming for half your plate to be covered by vegetables at main meals
  • Consider swapping to a lower energy protein substitute option
  • Snack on permitted fruit or vegetables

Download the recipe booklet for tasty recipes which can be adapted to your exchanges and energy needs here.

Pregnancy is an exciting time, with a lot to consider especially when you have PKU, planning and being organised can help you as your pregnancy progresses.

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