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Birth defect

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Birth defects (or con defects) are defects in a baby at birth, or which develop in the first month of life.[2]

There are two main types of con defect. The first is caused by genetic abnormalities, which are hereditary. The second is caused by conditions (such as infectious diseases) which a baby gets from its mother.[3]

Sometimes doctors can find out that a baby has a con 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

Another type of genetic defect is caused by errors in chromosome copying during the cell division which produces the gametes (meiosis). 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. For example, If a pregnant woman gets rubella, her child can have many birth defects.

As time passes, 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.

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.

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 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]

Related pages


  1. "WHO Disease and injury country estimates". World Health Organization. 2009. Retrieved Nov. 11, 2009.
  2. Graham, John Whichello 2007. Smith's recognizable patterns of human deformation.. 3rd ed, Philadelphia: Saunders. pp. 3. ISBN 0-7216-1489-2 .
  3. 3.0 3.1 Kliegman R.M. et al 2002. Nelson's essentials of pediatrics. 5th ed, Elsevier Saunders. p. 148; 229.
  4. Centers for Disease Control and Prevention. Birth defects research.
  5. Inheritance of genetic disorders. Teachers' Domain 2012. [1]
  6. Crider K.S. et al 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 .
  7. Rutecki, Gregory W. 2010. "Pre-Prenatal Care: a primary care primer on the future". Retrieved 25 September 2010.
  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.
  11. Francis O. 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 .
  12. "Miscarriage: causes of miscarriage". Retrieved 18 September 2007.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.
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