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Important information for women with Phenylketonuria (PKU)

Patient information A-Z

Having sex or planning to have sex in the future? Read on….

Why are we giving you this information?

Women with PKU can get pregnant just like anyone else.

If you are not planning a baby, talk to your GP about contraception. There are plenty of forms of contraception that are safe for you to use.

If you are planning a pregnancy, we want this to be an enjoyable and safe experience for you. We encourage you to contact a member of the metabolic team at least three months before you decide to stop contraception.

Why all the fuss?

If women with PKU are not on a low protein diet (low phenylalanine diet) they will have high levels of phenylalanine in the blood. This high concentration of phenylalanine will cross to the baby's placenta and can interfere with the normal development of the baby and can result in long-term or permanent damage. This happens very early on in the pregnancy, often before the mother knows she is pregnant.

The main abnormalities associated with high blood phenylalanine in the mother are:

  • congenital heart disease
  • damage to the brain
  • small head
  • low birth weight
  • non- sustainable pregnancy

Since the development of the vital organs occurs early on in the pregnancy, in order to achieve the best possible outcome,

phenylalanine levels should be controlled

before you decide to get pregnant.

What if I am pregnant and did not plan it?

Don’t panic….

  • Contact the metabolic team as soon as you find out and we will see you as soon as possible to give you support, information and care.
  • Move to zero protein exchanges.
  • The most important thing is to reduce your phenylalanine levels.,
  • Ensure you are taking your protein substitutes drinks/gels or powder. If you do not have any let the team know.,
  • Inform your GP and request a prescription of 5mgs folic acid.
  • Start sending blood spots in to the hospital three times a week.

Monitoring your blood phenylalanine levels

Frequent monitoring of your phenylalanine allows the metabolic team to help you adjust your diet as required. This will help us ensure that you can safely become pregnant.

The metabolic team will arrange for you to have outpatient appointments during this time as needed to help you achieve the desired levels and help you with any issues that you’re are experiencing.

We are aiming for you to monitor your phenylalanine levels three times a week when preparing for pregnancy and during pregnancy in order that these should be kept below 300µmol/L.

This may seem daunting but we can help you at every step along the way.

Remember your metabolic team are here to help you have an enjoyable pregnancy and a healthy baby.

It can be very distressing to have an unplanned pregnancy when you have PKU.

Get in contact with us before you stop using contraception. Even if you are not actively planning a pregnancy.

Useful link

The National Society for Phenylketonuria (NSPKU) have some excellent resources on their website (opens in a new tab)

Contact telephone: 03030401090

Metabolic Team contacts

Specialist dietitians

Sarah Donald and Lisa Gaff on 01223 348769

Specialist nurses

01223 274634

Metabolic LDU unit

01223 274634

Email the Metabolic LDU unit

We are smoke-free

Smoking is not allowed anywhere on the hospital campus. For advice and support in quitting, contact your GP or the free NHS stop smoking helpline on 0800 169 0 169.

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Help accessing this information in other formats is available. To find out more about the services we provide, please visit our patient information help page (see link below) or telephone 01223 256998.

Contact us

Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151