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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