Birth defect

condition present at birth regardless of cause; human disease or disorder developed prior to birth

A birth defect (or congenital disorder) is a defect in a baby at birth, or which develops in the first month of life.[2]

Congenital anomalies per 100,000 inhabitants in 2004.[1]
  no data
  less than 160
  more than 950
Charles II of Spain was born mentally and physically disabled, probably caused by inbreeding in the House of Habsburg

The term is neutral as to whether the cause is genetic (inherited birth defect) or environmental (causes in the environment, that is, outside the foetus). If a condition is said to be "congenital", that is neutral language. Often it is not known what causes a condition found at birth. In common use, it is often redirected to "birth defect". That term is also neutral as to cause.

There are two main types of congenital defect. The first is caused by genetic abnormalities, which are hereditary. The second may be caused by conditions (such as infectious diseases) which a baby may get.[3] However, we may not know what caused the condition.

Sometimes doctors may find out that a baby has a congenital disorder before its birth. They use prenatal diagnosis and screening tests, such as amniocentesis.[4]

Genetic defects


Lethal or damaging genes


Some gene alleles (versions of a gene) can damage the baby.

Conditions like dwarfism are nearly always genetic in origin. One type, achondroplasia, happens when a child's bones does not grow correctly. Another type is caused by pituitary malfunction, where the pituitary gland, which puts out growth hormones, does not work properly.[5]

Many genetic disorders are caused by mutations (or changes) in gene alleles. Mutations can cause development to go wrong, or a simple biochemical deficiency (the body does not have enough of an important chemical). In the case of a chemical deficiency, the problem may be curable. For example, phenylketonuria was a cause of mental retardation. Doctors came up with a simple test to find which babies have this condition. They found that if these children got treated and followed a strict diet, they could get enough of the chemical they needed. Phenylketonuria now causes few cases of mental retardation.

Chromosome defects


Cells divide and copy themselves to produce gametes. Sometimes, errors happen in the way that chromosomes are copied during this process. These errors are then copied again and again as cells keep dividing and copying themselves. The most common chromosomal disorder is Down syndrome ('Mongolism'). This condition happens when a child has three copies of the 21st chromosome, instead of two.

Infectious diseases


The other main type of congenital disorder is caused by an infectious disease being passed from mother to child. For example, If a pregnant woman gets rubella, her child can have many birth defects. Congenital syphilis was common a century ago, and congenital AIDS occurs today, and is common in some parts of Africa.

Screening and antibiotics has caused the number of infections transmitted by the mother to drop. It is a much smaller proportion than a century ago, despite AIDS. Also, maternal nutritional defects are much rarer, except in countries where food supply is limited. Therefore, genetic disorders have grown as a proportion of the total congenital defects.

Substances taken by the mother




Sometimes mothers take chemicals which cause the embryo damage.[6] Any substance that causes birth defects is known as a teratogen.

Drugs taken by the mother may affect development of the embryo. Pregnant women are not allowed to use some drugs. For example, thalidomide should not be used by a pregnant woman, or it can cause many defects in the foetus.



If the mother took certain things during pregnancy, these can lead to problems with the baby. Common examples of such things are smoking tobacco, or drinking alcohol. Food related: Pregnant women should eat well. If a pregnant woman does not receive enough folic acid with her food, the child can get neural tube defects.

Sensible precautions


Many women give up cigarettes and alcohol when pregnant, because this gives the embryo a better chance of developing normally.[7]

How common birth defects are


About 3 percent of all babies have what is called a major physical anomaly. This is something that damages the way the baby looks, or how it functions (its physiology).[8]

Birth defects involving the brain are the most common problems. They concern about 10 per 1000 live births, compared to heart problems, at 8 per 1000, kidney problems at 4 per 1000, and limbs at 1 per 1000. All other physical anomalies together occur in 6 per 1000 live births. The human brain has had changes and expansion fairly recently in evolutionary terms.

Birth defects of the heart have the highest risk of death during childhood. They are the cause of 28% of infant deaths due to birth defects. chromosomal abnormalities and respiratory abnormalities each account for 15%, and brain malformations about 12%. About 10% of deaths in children are because of a genetic disease. This is (in modern times) more than the number of deaths caused by infectious diseases.[3]

China Birth Deformity Monitoring Centre says that one baby with birth defects is born every 30 seconds in China.[9]



Pregnancies which do not come to term (miscarriages) have similar causes to birth defects. Many will be due to failures in the genetics controlling development of the embryo.

Most clinically apparent miscarriages (two thirds to three-quarters in various studies) occur during the first trimester.[10][11] Chromosomal abnormalities are found in more than half of embryos miscarried in the first 13 weeks.

A pregnancy with a genetic problem has a 95% probability of ending in miscarriage.[12] Genetic problems are more likely to occur with older parents; this may account for the higher miscarriage rates observed in older women.[13]



  1. "WHO Disease and injury country estimates". World Health Organization. 2009.
  2. Graham, John Whichello 2007 (2007). Smith's recognizable patterns of human deformation. 3rd ed, Philadelphia: Saunders. pp. 3. ISBN 978-0-7216-1489-2.{{cite book}}: CS1 maint: location (link) CS1 maint: numeric names: authors list (link)
  3. 3.0 3.1 Nelson's essentials of pediatrics. 5th ed, Elsevier Saunders. 2015. p. 148; 229. {{cite book}}: Cite uses deprecated parameter |authors= (help)
  4. Centers for Disease Control and Prevention. Birth defects research.
  5. "Inheritance of genetic disorders. Teachers' Domain 2012". Archived from the original on 2013-07-10. Retrieved 2013-06-30. {{cite web}}: More than one of |archivedate= and |archive-date= specified (help); More than one of |archiveurl= and |archive-url= specified (help)
  6. Crider K.S. et al. 2009 (2009). "Antibacterial medication use during pregnancy and risk of birth defects: National Birth Defects Prevention Study". Arch Pediatr Adolesc Med. 163 (11): 978–85. doi:10.1001/archpediatrics.2009.188. PMID 19884587.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  7. Rutecki, Gregory W. 2010. "Pre-Prenatal Care: a primary care primer on the future". Archived from the original on 9 November 2012. Retrieved 25 September 2010. {{cite web}}: More than one of |archivedate= and |archive-date= specified (help); More than one of |archiveurl= and |archive-url= specified (help)CS1 maint: numeric names: authors list (link)
  8. Kumar, Abbas and Fausto (eds) Robbins and Cotran's pathologic basis of disease, 7th edition, p.470.
  9. "Chinese babies born with birth defects every 30 seconds". 30 October 2007.
  10. Rosenthal, M. Sara 1999. "The second trimester". The gynecological sourcebook. WebMD. Retrieved 18 December 2006.{{cite web}}: CS1 maint: numeric names: authors list (link)
  11. Francis O. 1959 (1959). "An analysis of 1150 cases of abortions from the Government R.S.R.M. Lying-in Hospital, Madras". J Obstet Gynaecol India. 10 (1): 62–70. PMID 12336441.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  12. "Miscarriage: causes of miscarriage".]. Archived from the original on 28 July 2010. Retrieved 18 September 2007. {{cite web}}: More than one of |archivedate= and |archive-date= specified (help); More than one of |archiveurl= and |archive-url= specified (help) taken word-for-word from pp. 347-9 of: "Chapter 27. What to do when miscarriage strikes". The PDR Family Guide to Women's Health and Prescription Drugs. Montvale, NJ: Medical Economics. 1994. pp. 345–50. ISBN 1-56363-086-9.
  13. "Pregnancy over age 30". MUSC Children's Hospital. Archived from the original on 13 November 2006. Retrieved 18 December 2006.