Fetal Hydantoin Syndrome

What is fetal hydantoin syndrome?

Fetal hydantoin syndrome refers to a collection of features that affect babies who were exposed to certain antiseizure medications during pregnancy — specifically, a medication called phenytoin (Dilantin®). Phenytoin is what healthcare providers call a teratogen, or a substance that can disrupt normal fetal development.

Some features of fetal hydantoin syndrome are visible at birth. These include birth defects (congenital malformations) affecting your baby’s face, head, fingers and toes.

Other features might not be noticeable right away. These include developmental delays and intellectual disabilities. Healthcare providers work with families to identify the cause and provide appropriate treatment and support.

It’s important to know that most babies exposed to these medications don’t develop fetal hydantoin syndrome. But because there’s a risk, your healthcare provider will closely monitor your pregnancy and possibly make changes to your medications.

You should never stop taking your medications unless your healthcare provider tells you to. Doing so can be dangerous both for you and your developing fetus. Your provider will adjust your dosage as needed or switch you to another medication. Follow their guidance and ask if there’s anything you don’t understand.

How common is fetal hydantoin syndrome?

Fetal hydantoin syndrome affects 5% to 11% of fetuses exposed to phenytoin.

Numbers and statistics only tell part of the story. Healthcare providers typically look at the bigger picture when considering the effects of antiseizure medications on pregnancy. In other words, it’s not as useful to look at how common a specific syndrome might be. Instead, providers care about all the possible effects of many different antiseizure medications — alone and in combination.

For example, taking multiple antiseizure medications can be riskier than taking just one. And some medications (like valproate products) are more likely to cause serious effects compared with other medications.

Your healthcare provider can tell you more about how your medications might affect your pregnancy, specifically. They’ll determine your risks and tailor guidance to your unique situation.

What are the signs and symptoms of fetal hydantoin syndrome?

Signs of fetal hydantoin syndrome that are present at birth may include:

• Eyes that are farther apart than expected (hypertelorism).
• Crossed eyes (strabismus).
• Cleft lip and/or cleft palate.
• A nasal bridge that’s flatter or wider than expected.
• Head size that’s smaller than expected (microcephaly).
• Underdeveloped or malformed fingers, toes and nails.

As your baby grows, you may notice signs or symptoms of developmental delays. A developmental delay is when your baby is slow to reach one or more developmental milestones compared to other babies their age. Examples of milestones include smiling for the first time, rolling over or taking their first step.

You may also notice signs or symptoms of intellectual disability. An intellectual disability affects how your child learns and interacts with the world around them. For example, your child may not catch on to toilet training or self-care activities as quickly as you might expect. Or, they might have difficulty understanding concepts like money or time management.

What causes fetal hydantoin syndrome?

Antiseizure medications that pass from a pregnant person to their fetus (via the placenta) cause fetal hydantoin syndrome.

Researchers don’t understand the exact mechanism, or how these medications lead to malformations and other changes. They believe other factors, like genetics, may also play a role. For example, genetic mutations may affect how your body breaks down medications. And this could determine how medications affect pregnancy.

Future research may shed light on how this syndrome develops and who’s most at risk.

How is fetal hydantoin syndrome diagnosed?

Healthcare providers diagnose fetal hydantoin syndrome at birth or during early childhood when a baby displays typical signs of the condition. They’ll use the birthing parent’s medical history (including medication use) to help make the diagnosis. There are no diagnostic tests specifically for fetal hydantoin syndrome.

Similarly, during the prenatal period, there’s no specific diagnostic test to confirm the presence of fetal hydantoin syndrome. But providers may suspect this syndrome based on birth defects they identify during this time.

What is the treatment for fetal hydantoin syndrome?

Healthcare providers will tailor treatment to your baby’s specific symptoms and needs. Treatments may change as your child gets older. Possible treatments include: 

• Surgery (for example, surgery to repair cleft lip and cleft palate).
• Medications.
• Physical therapy.
• Occupational therapy.

Your child may need some extra help with learning. Your child’s healthcare team will work with you to create an Individualized Family Service Plan (IFSP). This is a document that’s tailored to your child’s needs. It’ll include plans for any services your child might need, like assistive technology and speech therapy.

Healthcare providers that may work together to provide care for your child include:

• Pediatricians.
• Plastic surgeons.
• Maxillofacial surgeons.
• Child psychologists.
• Pediatric neurologists.
• Occupational therapists.
• Speech therapists.

Can fetal hydantoin syndrome be prevented?

It’s not always possible to prevent medications from harming a developing fetus, especially when you need such medications to protect your own health. Your healthcare provider will work with you to lower the risk of fetal hydantoin syndrome. For example, they may:

• Adjust your medications before pregnancy and/or while you’re pregnant. This might involve reducing the number of antiseizure medications you take. Or it might mean switching to different medications with a lower risk of fetal harm.
• Advise you to take folic acid supplements before and during pregnancy to help protect against congenital malformations.

Your provider will closely monitor your pregnancy and make changes to your medications as needed. Be sure to go to all your appointments and share any questions or concerns.

What can I expect if my baby has fetal hydantoin syndrome?

Your baby’s healthcare team will tell you what you can expect based on your baby’s signs and symptoms. Your baby may need some surgeries early in life as well as some support services (like help with learning) as they get older.

Take things one step at a time. If you’re feeling overwhelmed or stressed, reach out to a therapist. They can talk through how you’re feeling and help you find healthy ways to manage stress.

When should I seek medical care?

If you’re taking antiseizure medications and it’s possible you could become pregnant or are planning for pregnancy, talk to a healthcare provider. They’ll review your medications and decide if you need to make changes.

If you’re pregnant and taking antiseizure medications, follow the appointment schedule your provider gives you. Follow-ups are very important so your provider can monitor your pregnancy and make changes to your medications as needed. They’ll do everything possible to prevent you from having seizures while minimizing the risk of fetal harm.

What questions should I ask my healthcare provider?

Questions you may want to ask before becoming pregnant include:

• Is pregnancy safe for me?
• What changes might I need to make to my medications?
• What are the chances that my medications will affect fetal development?
• When should I follow up with you?

Questions to ask if your baby is diagnosed with fetal hydantoin syndrome include:

• How will this condition affect my baby?
• What treatments do you recommend, and when?
• How can I care for my baby at home?
• How will this condition affect my child’s development or intellectual ability?
• What can I expect as my child gets older?

A note from Cleveland Clinic

Pregnancy comes with many unknowns. And when you’re living with a condition that requires medication, you might wonder how the medication will affect your baby. It’s possible that taking antiseizure medications while pregnant can lead to fetal hydantoin syndrome or other unintended effects. But it’s also possible — and more likely — that the medications won’t affect your pregnancy. Your healthcare provider can tell you more about what to expect and support you each step of the way.