Birth Defects
home >  maps & data >  birth defects
Types of Birth Defects

A baby may be born with a birth defect caused by a problem in their genes, chromosomes, metabolism, formation of external body parts (such as limbs) or internal organs, or all three. Here, we are focusing on a limited set of chromosomal and structural defects for which there is evidence of one or more environmental causes.

Neural Tube Defects: Anencephaly and Spina Bifida

Neural tube defects occur when this portion of the embryo, which forms the spine and brain, does not develop correctly very early in pregnancy. These birth defects are strongly linked to mothers' intake of folic acid.  For women planning pregnancy, a daily multivitamin with folic acid will lessen the risk of neural tube defects.

Anencephaly is a severe neural tube defect involving an incompletely formed skull and brain. Infants with anencephaly are unlikely to survive. This condition can be diagnosed via ultrasound in the first or second trimester of pregnancy. It is very rare, occurring in fewer than 3 in 10,000 pregnancies per year.

Spina bifida is a neural tube defect affecting the spine. There may be an opening along the infant's backbone exposing the spin, and surgery will be required to close it. There may be other problems associated with spina bifida, such as leg weakness or paralysis, or a collection of fluid in the brain or other conditions that will require ongoing care. This condition affects about 3 in 10,000 babies born each year.

Oral-Facial Clefts: Cleft Lip and Cleft Palate

Oral-facial clefts (a 'cleft' is a split or opening in an otherwise smooth surface) occur when the structures that form an infant's lip and/or mouth do not completely fuse during development. Clefts can range in size and severity and affect about 7,000 infants per year in the United States.

The causes of oral-facial clefts are not well understood. Both genes and environmental factors may impact the prevalence of oral-facial clefts. Research indicates that there may be an elevated risk when a pregnant woman takes certain anti-seizure drugs, smokes, drinks alcohol, or has a folic acid deficiency.

Surgery can correct many oral-facial clefts and usually occurs within 3 to 18 months after birth. After surgery, many infants and children may have no further problems, while others may have ongoing challenges in feeding, oral health, hearing and speech.

Cleft lip occurs early in the pregnancy (fourth to seventh week), and may be small or large. Cleft palate (the top part of the mouth, behind the teeth) happens slightly later (sixth to ninth week), and also varies in size among affected newborns. Affected babies can have one or both of these conditions. Both conditions interfere with feeding and speech and will require surgery.

Down Syndrome

Down syndrome is a chromosomal defect that occurs when the egg or sperm divides incorrectly. Most cases (95%) are Trisomy 21, a condition in which the infant receives an extra copy of chromosome 21. Individuals with Down syndrome have 47 chromosomes instead of 46. Down syndrome affects about 1 in 700 infants per year in the United States (about 6,000 total).

Although the impact of this condition varies from person to person, individuals born with Down syndrome tend to have developmental and physical problems including: Characteristic facial features and physical appearance, cognitive disability, heart defects, intestinal malformations, vision and/or hearing impairment, and predisposition to other health conditions throughout the life course.

Down syndrome is often diagnosed through routine testing during pregnancy. The risk of having a baby with Down syndrome increases as the age of the mother increases (a baby born to a 40 year old mother has a higher risk of Down syndrome than a baby born to a 20 year old mother). However, because more younger women have babies than older women, more babies with Down syndrome are born to younger women. Other than maternal age, there are no known external factors linked to the occurrence of Down syndrome.


Hypospadias occurs in males when the opening of the urethra, the tube that carries urine from the bladder to the outside of the body, is located along the underside of the penis instead of at the tip. It is a relatively common birth defect, with approximately 5 in 1,000 male babies affected . The severity of this birth defect varies by location of the hypospadias. In mild cases, the problem is cosmetic rather than causing any functional problem after birth. When necessary, surgery is usually performed when the infant is between 6 to 18 months old.

The specific cause of any single case of hypospadias is unknown. However, research indicates that prenatal exposure to certain hormones, maternal age, maternal obesity such as may increase the risk of hypospadias.

Heart Defects: Hypoplastic left heart syndrome, tetralogy of Fallot, transposition of the great arteries

Heart defects are among the most common birth defects and are the leading cause of deaths related to birth defects. These defects affect about 40,000 infants per year in the United States, or about 1 in every 100 births. Heart defects develop in the early weeks of pregnancy when the baby's heart is forming. Heart defects may be detected prenatally using ultrasound, but most heart defects are diagnosed after birth. A heart abnormality rarely causes problems while the fetus is in the womb and may only become evident after birth. Most infants diagnosed with major heart abnormalities have surgery to correct the problem within the first few months of life. Some babies may have less severe heart defects that will repair without treatment.

Although the causes of most congenital heart defects are unknown, there are several environmental or external factors that may make these problems more likely. If, during pregnancy, a woman is exposed to rubella (German measles), influenza, or some other viral infections, drinks alcohol or uses cocaine, or takes certain prescribed medications, the risk of heart defect is higher than for babies not exposed to these factors. In addition, if a pregnant woman is exposed to chemical solvents such paint, varnish, and some cleaning products, the baby is at higher risk.

Hypoplastic left heart syndrome means that the left side of heart is underdeveloped and unable to work properly. This condition is very severe and must be corrected with surgery.

Tetralogy of Fallot is the name for one or more conditions that affect the flow of blood through the heart. Although this condition is present at birth, symptoms may not appear for several months. Infants may show poor growth, and they may have episodes in which some or all of their skin appears blue-ish ("cyanosis"). This defect is usually repaired with surgery in the first few months of life. In addition to the risk factors for all heart defects, poor prenatal nutrition and older maternal age increase the risk for tetralogy of Fallot.

Transposition of the great arteries is a heart defect that is present at birth, when the two main arteries carrying blood away from the heart are switched or transposed in position. These children will have other structural heart abnormalities along with the transposition. These defects are very severe, and these babies will require corrective surgery.


Gastroschisis is a birth defect that occurs when a portion of the infant's intestine is outside the body, usually near the belly button/umbilical cord. About 1,900 infants in the United States are born per year with this defect. Surgical correction is required. Infants and children who have had the condition corrected through surgery may face challenges moving digested food through the stomach and intestines and absorbing nutrients.

The causes of gastroschisis are not well understood. Some research has shown that very young mothers or mothers who consume a high fat and high cholesterol diet may be more likely to give birth to an infant with gastroschisis.

Limb Deficiencies

Limb (arm or leg) deficiencies or defects occur when a part of one or both limbs fail to form completely during pregnancy. The resulting limb is either much smaller than a normal size limb or missing. Arm deficiencies affect about 1,500 babies per year in the US, and an additional 750 babies per year have leg deficiencies. Treatment may include artificial limbs, splints or braces, surgery, and most children with this condition will have physical and occupational therapy.