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[[File:Congenital anomalies world map - DALY - WHO2004.svg|thumb|Congenital anomalies per 100,000 inhabitants in 2004.<ref>{{cite web |url=http://www.who.int/healthinfo/global_burden_disease/estimates_country/en/index.html |title=WHO Disease and injury country estimates |year=2009 |work=World Health Organization |accessdate=Nov. 11, 2009}}</ref><div class="references-small" style="-moz-column-count:3; column-count:3;">
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[[File:Rey_Carlos_II.jpg|thumb|[[Charles II of Spain]] was born mentally and physically disabled, probably caused by [[inbreeding]] in the [[House of Habsburg]]]]

'''Birth defects''' (or '''congenital defects''') are defects in a [[baby]] at birth, or which develop in the first month of life.<ref name="isbn0-7216-1489-2">{{cite book |author=Graham, John Whichello 2007 |title=Smith's recognizable patterns of human deformation. |publisher= Saunders |location= 3rd ed, Philadelphia |pages=3 |isbn=0-7216-1489-2 |oclc= |doi= |accessdate=}}</ref>

There are two main types of congenital defect. The first is caused by [[Genetic disorder|genetic abnormalities]], which are [[hereditary]]. The second is caused by conditions (such as [[infectious disease]]s) which a baby gets from its mother.<ref name=Nelson>{{cite book|title=Nelson's essentials of pediatrics|authors = Kliegman R.M. et al. 2002 |page = 148; 229|publisher = 5th ed, Elsevier Saunders}}</ref>

Sometimes doctors can find out that a baby has a congenital disorder before its birth. They use [[prenatal diagnosis]] and [[screen]]ing tests, such as [[amniocentesis]].<ref name="cdc">Centers for Disease Control and Prevention. [https://www.cdc.gov/ncbddd/bd/research.htm Birth defects research].</ref>

== Genetic defects ==
=== Lethal or damaging genes ===
Some [[gene]] [[allele]]s (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 [[bone]]s does not grow correctly. Another type is caused by [[pituitary]] malfunction, where the pituitary [[gland]], which puts out growth [[hormone]]s, does not work properly.<ref>[http://www.teachersdomain.org/resource/tdc02.sci.life.gen.lp_disorder/ Inheritance of genetic disorders. ''Teachers' Domain'' 2012]</ref>

Many [[genetic disorder]]s are caused by [[mutation]]s (or changes) in gene [[allele]]s. 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 [[gamete]]s ([[meiosis]]). [[Cell]]s [[cell division|divide]] and copy themselves to produce [[gamete]]s. 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.

== Maternal [[environment]] ==
=== 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]].

As time passes, screening and [[antibiotics]] has caused the number of [[infection]]s transmitted by the mother to drop. It is a much smaller proportion than a century ago, despite AIDS. Also, maternal [[nutrition]]al 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 ===
==== Chemicals ====
Sometimes mothers take chemicals which cause the [[embryo]] damage.<ref>{{cite journal |author=Crider K.S. et al. 2009 |title=Antibacterial medication use during pregnancy and risk of birth defects: National Birth Defects Prevention Study |journal=Arch Pediatr Adolesc Med |volume=163 |issue=11 |pages=978–85 |pmid=19884587 |doi=10.1001/archpediatrics.2009.188 |url=}}</ref> 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]].

=== Lifestyle ===
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 [[Smoking|cigarettes]] and [[alcohol]] when [[pregnant]], because this gives the embryo a better chance of developing normally.<ref>{{cite web |url=http://www.consultantlive.com/display/article/10162/1532211 |title=Pre-Prenatal Care: a primary care primer on the future |author= Rutecki, Gregory W. 2010 |publisher=ConsultantLive.com |accessdate=25 September 2010}}</ref>

== 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]]).<ref>Kumar, Abbas and Fausto (eds) ''Robbins and Cotran's pathologic basis of disease, 7th edition'', p.470.</ref>

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 [[limb]]s 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. [[Chromosome|chromosomal]] abnormalities and [[respiration|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 disease]]s.<ref name=Nelson/>

China Birth Deformity Monitoring Centre says that one baby with birth defects is born every 30 seconds in China.<ref>{{cite news
| url =| title = Chinese babies born with birth defects every 30 seconds| date = 30 October 2007}}</ref>

== Miscarriages ==
Pregnancies which do not come to term ([[miscarriage]]s) 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.<ref name="webmd">{{cite web | last = Rosenthal, M. Sara 1999| title = The second trimester | work = The gynecological sourcebook | publisher = WebMD | url = http://www.webmd.com/content/article/4/1680_51802.htm | accessdate = 18 December 2006 }}</ref><ref name="pmid12336441">{{cite journal |author=Francis O. 1959 |title=An analysis of 1150 cases of abortions from the Government R.S.R.M. Lying-in Hospital, Madras |journal=J Obstet Gynaecol India |volume=10 |issue=1 |pages=62–70 |pmid=12336441 |doi=}}</ref> 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.<ref name="PDR Family Guide 1994">{{cite web |author= |title=Miscarriage: causes of miscarriage |url=http://www.healthsquare.com/fgwh/wh1ch27p3.htm |publisher=[http://www.healthsquare.com/about.htm HealthSquare.com] |accessdate=18 September 2007}}taken word-for-word from pp. 347-9 of: {{cite book |author= |year=1994 |title=The PDR Family Guide to Women's Health and Prescription Drugs |location=Montvale, NJ |publisher=Medical Economics |isbn=1-56363-086-9 |chapter=Chapter 27. What to do when miscarriage strikes |pages=345–50}}</ref> Genetic problems are more likely to occur with older parents; this may account for the higher miscarriage rates observed in older women.<ref>{{cite web | title = Pregnancy over age 30 | work = MUSC Children's Hospital | url = http://www.musckids.com/health_library/hrpregnant/over30.htm | accessdate = 18 December 2006 |archiveurl = https://web.archive.org/web/20061113233603/http://www.musckids.com/health_library/hrpregnant/over30.htm |archivedate = 13 November 2006}}</ref>

== Related pages ==
* [[List of genetic disorders]]
* [[Complete Genomics]]

== References ==
{{reflist|2}}

[[Category:Health problems]]
[[Category:Genetic disorders| ]]
{{stb}}

Birth defect - Revision history

Prab: CSV import

Prab at 13:39, 19 March 2025

Kondreddy Naveen at 20:43, 29 March 2024