Fetal Hydantoin Syndrome: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 23, 2026.
What kind of doctor treats Fetal Hydantoin Syndrome?
A medical geneticist, a doctor who diagnoses conditions present from birth, often helps diagnose this syndrome. A pediatrician, a children's doctor, also helps. A care team may also include neurologists (brain and nerve doctors) and surgeons. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What is fetal hydantoin syndrome?
Fetal hydantoin syndrome (FHS) may occur in children exposed to the seizure medicine phenytoin in the womb. Phenytoin is also called Dilantin. This can affect how a child grows and develops.
Phenytoin is a teratogen. That is something in pregnancy that gets in the way of the baby's development. Most babies exposed to phenytoin in the womb do not get FHS.
Symptoms
Symptoms can differ a lot from person to person. Some signs may not show at birth. They may become clearer as the child grows. Signs that have been described include:
- Slower growth before birth, after birth, or both.
- A smaller than average head size, called microcephaly.
- Face differences, which may be very subtle. Examples are a broad or flat nose bridge, a short nose, and wide-set eyes.
- Cleft lip, cleft palate, or both. These are openings in the upper lip or the roof of the mouth.
- Early delays, such as late rolling over, sitting, crawling, walking, or talking.
Causes and who gets it
FHS occurs when a developing baby is exposed to phenytoin during pregnancy. No known dose of phenytoin has been shown to be completely safe from causing these effects.
For many pregnant people with epilepsy, staying on seizure medicine is often needed to prevent seizures. Seizures can be very risky for both the pregnant person and the baby.
How doctors diagnose it
No lab test or genetic test can definitely confirm FHS. Doctors rely on a history of phenytoin use during the pregnancy. They also look at the child's physical, developmental, and nerve-related features.
Treatment
There is no single standard treatment. Care is tailored to each person.
- Early help, such as physical, occupational, and speech therapy, is advised for a child's development.
- A cleft lip or palate, when present, is repaired with standard surgery in infancy or early childhood.
- Ongoing medical care and support at school are often needed through childhood and beyond.
To lower the risk, doctors advise one seizure medicine at the lowest effective dose when possible, before and during pregnancy. Folic acid before and during pregnancy is advised for all pregnant people, even those taking phenytoin.
When to see a doctor
If you take a seizure medicine and are pregnant or planning to be, talk to your provider before you stop or start any medicine.
Call 911 or go to the emergency room if your child has a seizure, trouble breathing, or loses consciousness. A child with delays in rolling over, sitting, crawling, walking, or talking should be seen by a pediatrician.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Such a doctor can review medicine history and follow up. The doctor can also help coordinate a neurologist, an obstetrician, or a child's specialists.
Common questions
Do all babies exposed to phenytoin get fetal hydantoin syndrome?
No, most babies exposed to phenytoin in the womb do not get FHS. Studies estimate that about 5-10% of exposed pregnancies result in FHS.
Is there a test for fetal hydantoin syndrome?
No, no lab test or genetic test can definitely confirm FHS. Doctors rely on the history of phenytoin use in pregnancy and the signs they see.
Can fetal hydantoin syndrome be prevented?
Not fully, but the risk can be lowered. No dose of phenytoin is known to be completely safe in pregnancy. Doctors recommend one seizure medicine at the lowest effective dose, plus folic acid.
Should I stop my seizure medicine if I am pregnant?
No, do not stop it on your own. Talk to your provider first. Staying on seizure medicine is often needed to prevent seizures. Seizures can be very risky for both the pregnant person and the baby.
Does fetal hydantoin syndrome affect learning?
It can, but abilities vary widely, from typical intelligence to borderline or mild intellectual disability.
Sources
- National Organization for Rare Disorders (NORD) - Fetal Hydantoin Syndrome
- MedlinePlus - Pregnancy and Medicines
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
