Birth defects are abnormalities that occur during fetal development. They can affect a baby’s overall health, how the body looks, works or both. Approximately 1 in every 33 babies is born with a birth defect in the United States each year. While some birth defects have unknown causes, there are two key factors that can increase the risk of birth defects: genetics and the mother’s health/exposures during pregnancy.
Genetics
Genetics play a major role in determining whether a baby will be born with a birth defect. A birth defect can occur if there is a missing gene or piece of DNA, if genes are duplicated or rearrange incorrectly, or if genes mutate and function abnormally. There are many different types of genetic problems that can lead to birth defects, including:
- Inherited defects – These occur when a gene mutation is passed down to the baby from a parent. Examples include cystic fibrosis, sickle cell anemia, Tay-Sachs disease and thalassemia.
- New gene mutations – Sometimes a gene mutation develops randomly when a baby’s cells divide and the chromosomes duplicate. The mutation will be present in every cell of the baby’s body. An example is achondroplasia, a form of dwarfism.
- Chromosomal abnormalities – Errors during cell division can result in extra, missing or rearranged chromosomes. Down syndrome is an example of a chromosomal defect.
- Multifactorial inheritance – Sometimes a combination of small mutations in multiple genes, often coupled with environmental factors, work together to cause a birth defect. Examples include heart defects, cleft lip and palate, and neural tube defects like spina bifida.
If one or both parents have a gene mutation or chromosomal abnormality, they have an increased chance of passing it along to their baby and causing a birth defect. Parents may or may not be aware they are carriers. Some genetic problems are more likely to occur with advanced parental age, especially over age 35, due to more opportunity for genetic mutations over time.
Common Genetic Birth Defects
Here are some of the most common types of genetic birth defects:
- Down syndrome – Caused by an extra copy of chromosome 21. Characteristics include intellectual disability, distinctive facial features and low muscle tone.
- Cleft lip and cleft palate – Opening or split in the upper lip and roof of the mouth. Can affect breathing, hearing, speech and dental development.
- Sickle cell disease – Abnormal, crescent shaped red blood cells. Can cause pain, infections, fatigue, delayed growth and other issues.
- Cystic fibrosis – Thick, sticky mucus builds up and causes issues in lungs, pancreas, liver and intestines.
- Tay-Sachs disease – Progressive destruction of nerve cells in the brain and spinal cord.
- Heart defects – Improperly formed or missing parts of the heart. May need surgery after birth for repair.
- Spina bifida – Incomplete closing of the spine and membranes around the spinal cord. Can cause paralysis below the defect.
- Muscular dystrophy – Group of diseases causing muscle weakness and loss of muscle tissue.
- Hemophilia – Lack of ability to form blood clots due to missing blood clotting factors.
- Thalassemia – Reduced ability to produce hemoglobin and red blood cells.
Mother’s Health and Exposures During Pregnancy
The health of the mother during pregnancy is also a major factor that influences whether birth defects develop. Poor maternal health, inadequate nutrition, chronic health conditions, infections and harmful exposures can all put a developing baby at risk. Some key risks include:
- Chronic health conditions – Diseases like diabetes and epilepsy that are not well controlled increase the risk of complications and birth defects.
- Infections – Rubella, cytomegalovirus and toxoplasmosis can cross the placenta and cause fetal infection.
- Medications and drugs – Prescription drugs, over the counter medications and street drugs can potentially cause birth defects.
- Alcohol abuse – Drinking during pregnancy raises the risk of fetal alcohol spectrum disorders.
- Smoking – Cigarette smoking can affect fetal development and cause premature birth and low birth weight.
- Radiation exposure – X-rays and radiation therapy can increase birth defect risks.
- Chemical exposures – Pesticides, heavy metals like lead and mercury, and organic solvents are hazardous.
- Poor nutrition – Lack of key nutrients like folic acid can disrupt fetal growth.
- Advanced maternal age – Pregnancies over age 35 have higher risks due to aging eggs.
- Birth defects in previous pregnancies – Raises the chances of having another affected pregnancy.
Specific Birth Defects Related to Maternal Health
Some examples of birth defects that are directly influenced by the mother’s health and exposures during pregnancy include:
- Neural tube defects – Spina bifida, anencephaly. Caused by insufficient folic acid.
- Congenital heart defects – Formation errors in the heart’s chambers or vessels. Linked to maternal obesity and diabetes.
- Cleft lip/palate – Potentially related to medications, smoking, alcohol use and lack of folic acid.
- Limb reduction defects – Underdeveloped or missing limbs. Associated with pregestational diabetes.
- Gastroschisis – Hole in the baby’s abdominal wall. More common in young mothers and with smoking.
- Pyloric stenosis – Blocked stomach outlet. Related to smoking and substance abuse.
- Clubfoot – Twisted feet. Possible ties to smoking and diabetes.
- Eye/vision defects – Formed incorrectly during development. Linked to infections and alcohol.
Conclusion
Genetics and maternal health are the two primary factors that contribute to many types of birth defects. Genetic mutations and chromosomal abnormalities can be passed down to a developing baby and disrupt normal development. Additionally, chronic conditions, infections, malnutrition, smoking, alcohol use, medications and other exposures during pregnancy can trigger birth defects by interfering with fetal growth. While some birth defects cannot be prevented, following recommendations to optimize health before and during pregnancy can reduce the risks.