Phenylketonuria (also called PKU) is a condition in which your body can’t break down an amino acid called phenylalanine. Amino acids help build protein in your body. Without treatment, phenylalanine builds up in the blood and causes health problems.
Maternal PKU means that a woman who has PKU is pregnant. About 3,000 women of childbearing age in the United States have PKU.
PKU is inherited. This means it’s passed from parent to child through genes. A gene is a part of your body’s cells that stores instructions for the way your body grows and works. Genes come in pairs — you get one of each pair from each parent.
Sometimes the instructions in genes change. This is called a gene change or a mutation. Parents can pass gene changes to their children. Sometimes a gene change can cause a gene to not work correctly. Sometimes it can cause birth defects or other health conditions. A birth defect is a health condition that is present in a baby at birth.
You have to inherit a gene change for PKU from both parents to have PKU. If you inherit the gene from just one parent, you have the gene change for PKU, but you don’t have PKU. When this happens, you’re called a PKU carrier. A PKU carrier has the gene change but doesn’t have PKU.
Yes. But it depends on both you and your partner. If you and your partner both have PKU, your baby will have PKU.
If you and your partner are both PKU carriers, there’s a:
- 3-in-4 chance (75 percent) that your baby won’t have PKU
- 1-in-2 chance (50 percent) that your baby won’t have PKU but will be a PKU carrier
- 1-in-4 chance (25 percent) that your baby will have PKU
- 1-in-4 chance (25 percent) that your baby will not have PKU and not be a carrier
A genetic counselor can help you understand your chances of passing PKU to your baby. A genetic counselor is a person who is trained to help you understand about how genes, birth defects and other medical conditions run in families, and how they can affect your health and your baby's health.
Ask your health care provider if you need help finding a genetic counselor. Or contact the National Society of Genetic Counselors.
Yes. When a pregnant woman’s phenylalanine levels get too high, they can cause serious problems in her baby, including:
You may not know if you’re a PKU carrier. If you’re a carrier, you don’t have any signs or symptoms of PKU and you do not have PKU.
There are two types of tests that can tell you if you’re a PKU carrier. Both are safe to take during pregnancy. Your partner can have the tests, too.
- A blood test
- A swab of cells inside your mouth. This means your provider rubs a cotton swab against the inside of your cheek to get some cells.
You and your partner may want to be tested if PKU runs in either of your families. To help you find out, take your family health history. This is a record of any health conditions and treatments that you, your partner and everyone in both of your families have had. Use this family health history form and share it with your health care provider.
Yes. If you or your partner has PKU or is a PKU carrier, you can have a prenatal test to find out if your baby has PKU or is a carrier. You can have either of these tests:
- Chorionic villus sampling (also called CVS). This test checks tissue from the placenta for birth defects and genetic conditions. You can get CVS at 10 to 12 weeks of pregnancy.
- Amniocentesis (also called amnio). This test checks amniotic fluid from the amniotic sac around your baby for birth defects and genetic conditions. You can get this test at 15 to 20 weeks of pregnancy.
Talk to your provider or genetic counselor if you’re thinking of having either of these tests.
How is maternal PKU treated in pregnancy?
The good news is that most pregnant women who have PKU can have healthy babies if they follow their PKU meal plan. This is a special meal plan that is low in phenylalanine.
PKU meal plans are different for each person and depend on how much phenylalanine your body can take. Health care providers at a medical center or clinic that has a special program to treat PKU can help you create a PKU meal plan. These providers can monitor your pregnancy and help you change your meal plan to help keep your blood phenylalanine at the right level. Ask your health care provider for information on a medical center or clinic that treats PKU.
Your health care provider may order ultrasound tests during your pregnancy to check on your baby’s growth.
Be sure to follow your PKU meal plan at least 3 months before getting pregnant and throughout pregnancy. If you just found out you’re pregnant, go back to your PKU meal plan right away. You can get weekly blood tests during pregnancy to make sure your phenylalanine levels aren’t too high.
Last reviewed January 2013
See also: PKU (Phenylketonuria), Genetic counseling, Your family health history, Newborn screening
Most common questions
What is mononucleosis?
Mononucleosis (also called mono) is an infection usually caused by the Epstein-Barr virus (EBV). It’s sometimes caused by another virus called cytomegalovirus (CMV). EBV and CMV are part of the herpes virus family. Mono is most common in teenagers and young adults, but anyone can get it. Mono is called the “kissing disease” because it’s usually passed from one person to another through saliva. In addition to kissing, it can also be passed through sneezing, coughing or sharing pillows, drinks, straws, and toothbrushes.
You can have mono without having any symptoms. But even if you don’t get sick, you can still pass it to others. Symptoms can include:
- Achy muscles
- Belly pain
- Fatigue (feeling tired all the time)
- Sore throat
- Swollen glands in your neck
If your symptoms don’t go away or get worse, tell your health care provider. He’ll most likely do a physical exam and test your blood to find out for sure if you have mono.
There’s no vaccine to prevent mono. There’s also no specific treatment. The best care is to take it easy and get as much rest as you can. It may take a few weeks before you fully recover.
Can Rh factor affect my baby?
The Rh factor may be a problem if mom is Rh-negative but dad is Rh-positive. If dad is Rh-negative, there is no risk.
If your baby gets her Rh-positive factor from dad, your body may believe that your baby's red blood cells are foreign elements attacking you. Your body may make antibodies to fight them. This is called sensitization.
If you're Rh-negative, you can get shots of Rh immune globulin (RhIg) to stop your body from attacking your baby. It's best to get these shots at 28 weeks of pregnancy and again within 72 hours of giving birth if a blood test shows that your baby is Rh-positive. You won't need anymore shots after giving birth if your baby is Rh-negative. You should also get a shot after certain pregnancy exams like an amniocentesis, a chorionic villus sampling or an external cephalic version (when your provider tries to turn a breech-position baby head down before labor). You'll also want to get the shot if you have a miscarriage, an ectopic pregnancy or suffer abdominal trauma.
I had a miscarriage. How long should I wait to try again?
Before getting pregnant again, it's important that you are ready both physically and emotionally. If you don't need tests or treatments to discover the cause of the miscarriage, it's usually OK for you to become pregnant after one normal menstrual cycle. However, it may take longer for you to feel emotionally ready to be pregnant again. Everyone responds differently to a miscarriage. Only you will know when you are ready to try to get pregnant again.
Are gallstones common during pregnancy?
Not common, but they do happen. Elevated hormones during pregnancy can cause the gallbladder to function more slowly, less efficiently. The gallbladder stores and releases bile, a substance produced in the liver. Bile helps digest fat. When bile sits in the gallbladder for too long, hard, solid nuggets called gallstones can form. The stones can block the flow of bile, causing indigestion and sometimes serious pain. Staying at a healthy weight during pregnancy can help lower your risk of gallstones. Exercise and eating foods that are low in fat and high in fiber, like veggies, fruits and whole grains, can help, too. Symptoms of gallstones include nausea, vomiting and intense, continuous abdominal pain. Treatment during pregnancy may include surgery to remove the gallbladder. Gallstones in the third trimester can be managed with a strict meal plan and pain medication, followed by surgery several weeks after delivery.