About Maternal PKU
I am a woman with PKU, can I get pregnant and have children?
Yes! You can conceive, carry, and deliver a healthy baby if, before and during your pregnancy, you maintain a strict low-Phe diet, which means drinking all the formula as directed, and eating only the allowed foods. You must also get consistent health care before and during your pregnancy from your obstetrician or midwife.
What is Maternal PKU?
Maternal PKU is the medical term used when a woman who has PKU is pregnant.
Pregnant woman drinking low-Phe formula as part of a healthy diet for herself and her baby.
Should I stay on diet before I get pregnant, or just while I’m pregnant?
For the health of your developing baby, it is very important that you stay on diet before you get pregnant. When the Phe level in your blood is high, the blood travels to all parts of your body, including your uterus, where your baby develops. High Phe in your blood crosses over and is very harmful to your growing baby, even in the earliest weeks of pregnancy.
The safe blood Phe level for a woman with PKU to be pregnant is in the range of 120-360 µmol/L (micromoles per liter). Note: this same Phe range is sometimes shown as 2-6 mg/dL (milligrams per deciliter), since different health centers use different measurement units. It is important to know that it may take several weeks for you to lower your Phe levels to this safe range. During those weeks, your developing baby can already become damaged. That’s why, if you have PKU, you must plan your pregnancy ahead of time, and maintain a strict diet before you become pregnant.
As a woman planning to become a mother, it is up to you to bring your Phe levels under control before becoming pregnant, and to maintain low levels throughout your pregnancy.
If you become pregnant and are not on the diet, call your metabolic clinic as soon as possible to get back on treatment (formula and low-protein foods). Research shows that every week counts! The sooner you can get your blood Phe levels in control, the better it will be for your baby. Your baby has not necessarily been harmed. If you think you are pregnant, it’s a good idea to speak to your metabolic doctor even before you see your obstetrician or midwife.
Some pregnant women might benefit from supplemental treatment with BH4 (commercially known as Kuvan). This is a medication that can increase the activity of the enzyme (phenylalanine-hydroxylase) that does not work in PKU. You can discuss this with your metabolic doctor.
Do I have to take the formula before I’m pregnant and while I’m pregnant?
Yes! As you already know your PKU diet includes taking the formula throughout your life, to maintain your own health. If you have PKU and are planning to become pregnant, or if you already are pregnant, taking the formula is extremely important for the health of your baby.
Since, as a woman with PKU, you cannot metabolize (change) Phe, you must limit your intake of regular protein in foods. But protein is made of amino acids needed for your baby to grow during pregnancy. Since you can’t get these amino acids from regular food, you and your baby must get them from the formula. The formula contains all the important amino acids except Phe. During pregnancy you may need more formula than you usually do, so it is important to check with your clinic to make sure the diet you are following is correct. If you only restrict your protein intake while you’re pregnant but don’t take the formula, your Phe will not come down to a safe level for your unborn baby, and she will not get the amino acids she needs, so you will be putting her at risk.
What could happen to my developing baby if I have PKU and do not stay on diet or drink formula?
If you do not stay in Phe control during your pregnancy, your baby is at very high risk for mental retardation, small head size, heart defects and low birth weight. This table summarizes the risks:
The earlier in pregnancy you control your blood Phe, (bring it down to 120-360 µmol/L, or 2-6 mg/dL), and the more consistently you take the formula, the better your chances of having a healthy baby. Since the baby’s heart and other organs develop very early in pregnancy (by 8 weeks) it’s safest to be in good metabolic control before your pregnancy begins in order to prevent heart defects and other problems seen in babies of mothers with PKU.
Remember Every Week Counts for your baby’s health during your pregnancy:
The sooner you get in metabolic control of your Phe levels, the better for your baby
The sooner you stay on diet and take the formula consistently, the better
Getting in metabolic control before you become pregnant is best for your baby and you