context: Microcephaly is a rare nervous system disorder that causes a baby's head to be small and not fully developed. The child's brain stops growing as it should. This can happen while the baby is still in the mother's womb or within the first few years of birth. Your doctor may not be able to tell you why this happened to your baby. In most cases, the exact cause is unknown. It can be brought on by: A problem with your genes (congenital microcephaly) Something in your environment (acquired microcephaly) Congenital microcephaly is passed down through families. It's caused by defects in genes linked to early brain development. Microcephaly is often seen in children with Down syndrome and genetic disorders. Acquired microcephaly means the child's brain came into contact with something that harmed its growth and development. Some things that may do this while a baby is in the womb are: Viral infections, including rubella ( German measles), chickenpox, and possibly Zika, which is spread by mosquitos Parasite infections, such as toxoplasmosis or cytomegalovirus Toxic chemicals such as lead Not getting enough food or nutrients (malnutrition) Alcohol Drugs Acquired microcephaly can also be caused by other things, including: Hemorrhage or stroke in the newborn Injury to the brain after birth Spine or brain defects Your doctor may diagnose microcephaly before or after the baby is born. During pregnancy, an ultrasound may show that the baby has a smaller-than-expected head size. To see this clearly, it's best to have the test at the end of your 2nd trimester or when you're entering your last 3 months of pregnancy. After the baby is born, a health care worker will measure around the widest part of your child's head. The number is then marked on a growth chart. Doing this tells the doctor how your child's head is growing compared to other kids of the same age and sex. If your child's head measurement falls a certain point below the average, it's considered microcephaly. A head measurement is taken during every checkup until age 2 or 3. If your child has microcephaly, the size of his head will be checked at every doctor's visit. Children with a mild case may have a small head but no other problems. Your child's head will grow as he gets older. But it will remain smaller than what's considered normal. Some children have normal intelligence. Others have problems learning, but they usually don't get worse as your child gets older. Other symptoms may include: Balance and coordination problems Developmental delays (delayed sitting, standing, walking) Trouble swallowing and problems with feeding Hearing loss Hyperactivity (trouble paying attention or sitting still) Seizures Short height Speech problems Vision problems There's no cure for microcephaly, but there are treatments to help with development, behavior, and seizures. If your child has mild microcephaly, he'll need regular doctor checkups to monitor how he grows and develops. Children who have more severe cases need lifelong treatment to control symptoms. Some, like seizures, can be life-threatening. Your doctor will discuss treatments to keep your child safe and improve his quality of life. Your child may need: Medicines to control seizures and hyperactivity and to improve nerve and muscle function Speech therapy Physical and occupational therapy How well your child does depends on what caused the brain to stop growing in the first place. Children with a mild form of this disorder may have no other problems. They grow normally during childhood and adolescence and still meet age-appropriate growth milestones as they get older. Others can have severe problems with learning and moving. Children with microcephaly are more likely to have other medical problems, like cerebral palsy and epilepsy. While you're pregnant, you can take steps to try to prevent acquired microcephaly: Eat a healthy diet and take prenatal vitamins. Don't drink alcohol or do drugs. Stay away from chemicals. Wash your hands often, and get treated for any illness as soon as you feel sick. Have someone else change the litter box. Cat feces can spread the parasite that causes toxoplasmosis. Use insect repellent when in wooded areas or countries known for mosquitos. The CDC says insect repellent is safe to use while pregnant. If you have a child with microcephaly and wish to get pregnant again, talk to your doctor. Genetic counseling may help you understand your family's risk for the disease. Sometimes, talking to others in similar situations can help you better understand a disease or what to expect. The Foundation for Children with Microcephaly has a program that can put you in touch with other parents of a child with the disorder.