While still in the womb, some babies have problems with how their organs and body parts form, how they work, or how their bodies turn food into energy. These health problems are called birth defects.
There are more than 4,000 different kinds of birth defects, ranging from minor ones that need no treatment to serious ones that cause disabilities or require medical or surgical treatment. According to the March of Dimes, 1 out of every 33 babies born each year in the United States has a birth defect.
If a baby is born with a part of the body that is missing or malformed, it is called a structural birth defect. Heart defects are the most common type of structural defect. Others include spina bifida, cleft palate, clubfoot, and congenital dislocated hip.
When there is a problem with a baby's body chemistry, it is called a metabolic birth defect. Metabolic defects prevent the body from properly breaking down food to create energy. Examples of metabolic defects include Tay-Sachs disease, a fatal disease that affects the central nervous system, and phenylketonuria (PKU), which affects the way the body processes protein.
For people who want to become parents, it's important to know that some birth defects can be prevented. During a woman's pregnancy, taking folic acid and getting enough iodine in the diet can help prevent some types of birth defects. But it's also important to realize that most babies born with birth defects are born to two healthy parents with no obvious health problems or risk factors.
In most cases, doctors don't know what caused a baby's birth defect. When the cause is known, it might be environmental (such as a baby's exposure to chemicals or viruses while in the womb), a problem with the fetus' genes, or a combination of these things.
If a mother has certain infections (such as toxoplasmosis) during pregnancy, her baby can have a birth defect. Other conditions that cause defects include rubella and chickenpox (varicella). Fortunately, many people get vaccinated against these diseases so these infections are rare.
Also, alcohol abuse by the mother may cause fetal alcohol syndrome, and certain medicines taken by the mother can cause birth defects. (Doctors try to avoid harmful medicines during pregnancy, so a pregnant woman should tell any doctor she consults that she's expecting.)
Every cell in the body has chromosomes containing genes that determine a person's unique characteristics. During conception, a child inherits one of each pair of chromosomes (and one of each pair of the genes they contain) from each parent. An error during this process can cause a baby to be born with too few or too many chromosomes, or with a damaged chromosome.
One well-known birth defect caused by a chromosome problem is Down syndrome. A baby develops Down syndrome after getting one extra chromosome. Other genetic defects happen when both parents pass along a faulty gene for the same disease; this is called recessive inheritance and includes conditions such as Tay-Sachs disease and cystic fibrosis.
A disease or defect also can happen when only one parent passes along the gene for that disease. This is called dominant inheritance. This includes birth defects such as achondroplasia (a form of dwarfism) and Marfan syndrome (a disorder characterized by abnormally long fingers, arms, and legs).
Finally, some boys inherit disorders from genes passed onto them only by their mothers. These defects, which include conditions like hemophilia and color blindness, are called X-linked because the genes are carried on the X chromosome. Males have only one X chromosome, which is received from the mother, whereas females have two X chromosomes — one from each parent. A faulty gene on the X chromosome will be more likely to cause a problem in boys because they don't have a normal copy of the gene. Females who have an altered gene on one X chromosome and a normal gene on the other sometimes have mild features of the given defect.
Common Birth Defects
Cleft lip and/or palate happens when the tissues of the mouth or lip don't form properly during fetal development, leaving an opening, division, or split in that area. This is called "clefting." A cleft lip is a long opening between the upper lip and the nose. A cleft palate is an opening between the roof of the mouth and the nasal cavity. In the United States, oral clefting happens in 1 in 700 to 1,000 births, making it one of the most common major birth defects. Clefting can be surgically repaired after birth.
Cerebral palsy usually isn't found until weeks to months after birth. Kids with cerebral palsy have difficulty controlling the motions their muscles make — which muscles and how severely they are impaired varies from person to person. There's no cure for cerebral palsy, but therapies and other treatments can help kids improve their quality of life. The condition affects about 3 to 4 babies in every 1,000 born.
Clubfoot is a term used to describe a group of structural defects of the foot and ankle in which the bones, joints, muscles, and blood vessels are formed incorrectly. These defects range from mild to severe and may affect one or both feet. Feet affected by this defect most often point down, turn in, and have a limited range of motion. This is a relatively common birth defect, affecting about 1 to 3 in every 1,000 babies born each year in the United States. Boys are affected almost twice as often as girls. In most cases the cause is unknown, but some cases of clubfoot are a result of a genetic disorder or problems inside a mother's uterus that can affect or restrict the development of her baby's foot (for example, having too little amniotic fluid). This condition can be treated by applying a cast to the foot immediately after birth. This treatment works most of the time; if it doesn't, surgery and further casting are usually done.
Developmental dysplasia of the hip is when the round upper end of the thighbone doesn't sit inside the socket of the pelvis properly. This can happen in one or both hips and occurs in 1 in 1,000 births. While the exact cause is unknown, it tends to happen more in girls and runs in families. It's usually discovered at birth and treated soon after by placing the baby in a soft sling for 6 to 9 months. If it's not recognized and treated early, surgery may be necessary.
Congenital hypothyroidism, which occurs in about 1 in 3,000 to 4,000 births, happens when the baby's thyroid gland (located in the front of the neck) is absent or underdeveloped at birth or if a metabolic defect blocks production of thyroid hormone. This causes a lack of thyroid hormone, which is important for supporting normal growth and brain development. If this condition isn't recognized and treated with thyroid hormone medicines within the first few weeks of life, a baby will develop a developmental delay and permanent intellectual disability (mental retardation). Because of this, every state in the United States and most other countries routinely screen all newborns for hypothyroidism with a blood test taken shortly after birth.
Fetal alcohol syndrome (FAS) causes slowed growth, intellectual disability, abnormalities in facial features, and problems with the central nervous system. Every year between 2,000 and 12,000 babies in the United States are born with defects caused by alcohol. FAS cannot be cured or treated, but can be prevented by avoiding alcohol intake during pregnancy.
Neural tube defects (NTD) happen in the first month of pregnancy when the structure that develops into the brain and spinal cord is forming. Normally, this structure folds into a tube by the 29th day after conception. When the tube doesn't close completely, the baby has a neural tube defect. The two most common forms of this defect are:
- Spina bifida, which happens when the spinal column doesn't close completely around the spinal cord. It ranges from mild to severe and can be associated with loss of bladder and bowel function, paralysis, and in some cases, death.
- Anencephaly, which occurs in 3 out of 10,000 births, involves the lack of development of parts of the brain.
NTDs happen in roughly 1 out of every 3,000 live births. Many babies with these defects are stillborn or die soon after birth. Making sure a mother gets enough folic acid before and during pregnancy helps reduce the chances of a baby having an NTD.
Heart defects happen when a part of the heart fails to develop properly when a baby is in the womb. These include:
- atrial and ventricular septal defects, which are holes in the walls that separate the heart into its left and right sides
- patent ductus arteriosus, which happens when the tubular blood channel that allows the blood to bypass the lungs while the baby is in the womb doesn't close (as expected) after birth
- aortic or pulmonary valve stenosis, which are narrowings of the valves that allow blood to flow from the heart to the lungs and other parts of the body
- coarctation of the aorta, which is a narrowing of the aorta, the major blood vessel carrying blood from the heart to the rest of the body
- transposition of the great arteries, which is a reversal of the connections of the aorta and the pulmonary artery within the heart
- hypoplastic left heart system, which is when the side of the heart that pumps blood to the body is underdeveloped or nonexistent
- tetralogy of Fallot, which is a combination of four heart defects that involves restriction in the flow of blood to the lungs
Although the specific cause of most heart defects isn't known, doctors do know that many defects happen during the first trimester of pregnancy. The heart develops during the first 8-9 weeks of fetal growth, so these problems usually develop early on. Sometimes surgeons consult with parents about these conditions while a fetus is still in the womb. At birth, babies are routinely screened to check for normal blood oxygen levels right at birth and at 24 hours after birth, which has helped with early identification of congenital heart disease.
Exposure to certain medications (such as chemotherapy drugs, thalidomide, and the antiseizure drug phenytoin) during the first trimester of pregnancy may play a role in causing heart defects. Other causes include maternal alcohol abuse, rubella (German measles) infection, and diabetes during pregnancy.
Gastrointestinal Tract Defects
Gastrointestinal defects are structural defects that can happen at any point along the gastrointestinal tract, which is made up of the esophagus, stomach, small and large intestines, rectum, and anus. The incomplete or abnormal development of any of these organs can cause blockages that can lead to swallowing difficulties, vomiting, and problems with bowel movements.
Some of these defects are:
- esophageal atresia, or incomplete development of the esophagus
- diaphragmatic hernia, a defect in the layer of muscle separating the chest from the abdomen that allows some of the abdominal organs to protrude up into the chest
- pyloric stenosis, a condition in which the muscular wall of the passage carrying food from the stomach to the small intestine is abnormally thick and the passage narrow, forcing food back out through the esophagus (vomiting)
- Hirschsprung disease, in which a section of the large intestine is missing the nerves that control its contractions, resulting in severe constipation and sometimes bowel obstruction
- gastroschisis and omphalocele are defects in the abdominal wall that allow the intestine and other abdominal organs to protrude
- anal atresia involves lack of or incomplete development of the anus, causing it to be absent or smaller than it should be, often with the opening in the wrong place
- biliary atresia, in which the bile-carrying ducts in the liver either didn't develop or developed abnormally
Genetics play some role in all these defects, but it is unclear exactly how and to what degree. Early detection and treatment of these defects is important, as they can lead to serious health problems and even death if left untreated. Surgery is usually necessary to repair them.
Genetic Birth Defects
Cystic fibrosis (CF) affects cells in the lining of the skin and many of the passageways in the lungs, digestive system, and reproductive system. It causes these body parts to produce a thick, sticky mucus. Children with CF have frequent lung infections, problems digesting food, and poor weight gain. Treatment includes therapy to maintain lung function, get adequate nutrition, and prevent infections.
Down syndrome is a relatively common birth defect, affecting about 1 in 800 to 1,000 births. The chances of having a baby with Down syndrome increase dramatically with the age of the mother. Children with Down syndrome are born with an extra (third) copy of chromosome number 21 in their cells. They can have mild to severe symptoms and may have intellectual disability (mental retardation), distinctive physical features, heart defects, and other health problems.
Fragile X syndrome causes mental impairment that ranges from learning disabilities to intellectual disabilities (mental retardation), autistic behaviors, and problems with attention and hyperactivity. Physical characteristics of children with Fragile X include a long face, large ears, flat feet, and extremely flexible joints, especially fingers. Boys are affected more often than girls. There is no cure for Fragile X, although researchers are exploring ways to prevent it and deal with the complications.
Muscular dystrophy is a general term that's used to describe more than 40 different types of muscle diseases, all of which involve progressive weakness and degeneration (a breakdown) of the muscles that control movement. Heart muscles and some other involuntary muscles are also affected in some forms of muscular dystrophy, and a few forms also involve other organs. Almost all forms of the disorder are genetic and cannot be cured. Treatment includes physical and respiratory therapy, the use of assistive technology, and medications.
Phenylketonuria (PKU) affects the way the body processes protein and can cause intellectual disability (mental retardation). A baby born with PKU appears normal, but if the disease isn't treated, the child will suffer from developmental delays that are apparent by the first birthday. If the child is promptly treated with a special diet, intellectual disability can be prevented.
Sickle cell disease is a disorder of the red blood cells in which an abnormal sickle-like shape of the cells causes ongoing or chronic anemia (low blood count), periods of pain, and other health problems. Treatment may include taking antibiotics to prevent infection, blood transfusions, and bone marrow transplantation.
Tay-Sachs disease affects the central nervous system, causing blindness, dementia, paralysis, seizures, and deafness. It's usually fatal within the first few years of life. Babies with this disease appear normal when they are born; the symptoms develop during the first few months of life. Although there is no treatment for this disease, there's a test to help parents determine if they are carriers of the gene.
Infections That Cause Birth Defects
Infections during pregnancy can cause a variety of birth defects. These include:
- Congenital rubella syndrome, which poses the highest risk of fetal damage. In this syndrome, a child can have vision and/or hearing loss, heart defects, intellectual disability, and cerebral palsy. Because almost everyone is immunized against rubella, congenital rubella is almost never seen.
- Cytomegalovirus (CMV), probably the most common infection that shows up at birth. If a woman has this virus during pregnancy, her child may have low birth weight, intellectual disability (mental retardation) or learning disabilities, and hearing loss.
- Toxoplasmosis infection of the mother, which in her baby can cause eye infections that threaten vision, hearing loss, learning disabilities, enlarged liver or spleen, mental retardation, and cerebral palsy.
- Genital herpes virus infection of the mother, which can cause brain damage, cerebral palsy, vision or hearing impairment, and death of the baby if the virus is transmitted to the infant before or during the birth. Herpes complications are most commonly due to infection during the birth process and are not commonly classified as birth defects.
- Fifth disease, which can cause a dangerous form of anemia, heart failure, and in some cases fetal death.
- Congenital varicella syndrome, which is caused by chickenpox and can lead to scars, defects of muscle and bone, malformed and paralyzed limbs, a smaller-than-normal head, blindness, seizures, and intellectual disability (mental retardation). This is a rare occurrence in pregnant women who become infected with chickenpox.
- Congenital syphilis, which can become apparent when a child is a baby (early) or after age 2 (late). In early congenital syphilis, a child may be born prematurely or have an enlarged liver or spleen, inflammation of the nasal cartilage or "snuffles," bone changes, and central nervous system problems. A child with late congenital syphilis may have abnormalities of the facial bones and teeth, vision problems, and deafness.
Women who are pregnant should talk to their health care providers about ways to avoid these infections and what to do if they're exposed to them.
Diagnosing Birth Defects
Many birth defects are diagnosed even before a baby is born through prenatal tests. Prenatal tests also can help determine if a mother has an infection or other condition that is dangerous for the fetus. Knowing about a baby's health problems ahead of time can help parents and doctors plan for the future.
Defects that may be detected through prenatal screening include:
- neural tube defects (spina bifida, anencephaly)
- Down syndrome and other chromosome abnormalities
- inherited metabolic disorders
- congenital heart defects
- gastrointestinal and kidney malformations
- cleft lip or palate
- certain birth defects of the limbs
- congenital tumors
It's important to remember that screening identifies only the possibility that a baby has a defect. It's possible to give birth to a healthy baby after a screening test shows that a defect may be present. You aren't required to have any prenatal screening; talk to your doctor about any tests he or she thinks you should have.
Other birth defects that can't be detected before birth can be identified during routine newborn screenings. With parents' permission, babies are tested after birth to screen for certain birth defects that need to be treated soon after birth. Exactly what a baby is tested for varies from state to state, although all states screen for phenylketonuria (PKU), congenital hypothyroidism, sickle cell disease, and about 30 other conditions identified using a technology called tandem mass spectroscopy. Parents should ask health care providers or the hospital nursery which tests their state performs routinely.
Other disorders that states may test newborns for include:
- cystic fibrosis
- congenital adrenal hyperplasia (an inherited disorder of the adrenal gland that can cause severe illness in newborns if not diagnosed and treated within the first few weeks of life)
- hearing loss
Parents who have concerns about another specific birth defect might be able to have their baby tested for it. They should talk to their health care provider about it before the baby is born.
Preventing Birth Defects
Many birth defects can't be prevented, but a woman can do some things before and during pregnancy to help lower the chances of having a baby with a birth defect.
Before pregnancy, women should:
- make sure their vaccinations are up to date
- make sure they don't have any sexually transmitted diseases (STDs)
- get the daily recommended dose of folic acid before trying to conceive
- avoid unnecessary medicines and talk to their doctor about medicines they are taking
If there's a family history of birth defects or a woman is part of a high-risk group (due to age, ethnic background, or medical history), she should consider meeting with a genetic counselor to determine her baby's risk.
During pregnancy, it's important to take prenatal vitamins and eat a healthy diet in addition to taking the following precautions:
- don't smoke and avoid secondhand smoke
- don't drink alcohol
- avoid all illicit drugs
- get exercise and plenty of rest
- get early and regular prenatal care
By following these pregnancy precautions, women can help reduce their babies' risk of birth defects.