PKU Toolkit - A Guide to PKU Management for Teens and Young Adults - Produced by Children's Hospital Boston, Applied Nutrition, and the New England Consortium of Metabolic Programs

What is Maternal PKU?

Maternal PKU is the term used when a woman with PKU is pregnant. When planning to become pregnant, or already pregnant, the woman must maintain strict metabolic control both before and throughout her pregnancy to protect her baby.

Bringing a baby in the world is a wonderful experience. There is no reason for a woman with PKU not to enjoy this unique experience of her life. However, she needs to plan her pregnancy and be more careful and strict with her diet.

Let’s take a closer look at maternal PKU and answer some important questions.

Can a woman with PKU have children?
Yes, women with PKU can have healthy children if they maintain a strict diet and take the formula prior to and during pregnancy.

Why is it important to maintain the diet before, as well as during pregnancy?
A high blood phenylalanine level in the intrauterine environment is toxic to the developing fetus. If the pregnancy is not treated, the baby is likely to be born with mental retardation, small head size and heart defects. It may take several weeks for a woman with PKU to lower phenylalanine levels to 2-6 mg/dL. During those weeks, the fetus can be seriously damaged. That’s why women with PKU must plan their pregnancies very carefully and maintain strict diet even before pregnancy. However, in case of an unplanned pregnancy, a woman with PKU should still return to and maintain the strict diet as soon as possible.

These problems can be avoided and it is up to the mother to bring her phenylalanine levels under control before becoming pregnant if possible, and maintain low levels throughout pregnancy. Research shows that every week counts! So acheiving metabolic control as soon as possible is important!

Is taking the formula important?

BabyYes! The special PKU diet requires taking the formula throughout life. Specifically, for maternal PKU taking the formula is extremely important for having a healthy baby. Because a woman with PKU cannot metabolize the amino acid phenylalanine, she must limit her intake of regular protein. Protein is made of amino acids that are important for the body to grow, and therefore, the body needs to take them in another form. This is where the formula comes in. The formula is made of all the important amino acids except phenylalanine. It provides the necessary protein in a modified form that is needed for a health baby. Simply restricting phe intake without the formula will not protect the unborn child.  

What may happen to the unborn child if a woman does not maintain strict dietary control (phe restriction and formula)?
The earlier in pregnancy a woman maintains good blood phe control (2-6 mg/dL), the better are the chances for having a healthy baby. Women who are able to follow the strict diet well by 10 weeks gestation have had babies with normal growth and mental development. However, since the fetal heart develops very early in pregnancy (by 8 weeks gestation) it is safest to be in good control before pregnancy begins in order to prevent heart defects associated with maternal PKU.

Poor diet control

high phe diet, or
lack of formula

may cause in fetus
Heart problems

Small head size

Low birth weight

Mental retardation

Slow development

Language deficit

Our complete Maternal PKU & Pregnancy Guide is now online!

If you are a woman with phenylketonuria (PKU), and are planning to get pregnant, or already are pregnant, we created this guide for you! Developed by metabolic and nutrition specialists at Children’s Hospital Boston, the guide includes sections on PKU, Maternal PKU, genetics, newborn health, PKU recipes, and PKU & pregnancy resources. Being pregnant with PKU is challenging, but with careful planning ahead of time, and with the right diet, health care, and information, you can experience the wonder and joy of carrying and delivering a healthy baby.

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