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Viability is the ability of a fetus to survive outside the uterus without artificial support.[1][2]

Contents

Age

Stages in prenatal development, showing viability and point of 50% chance of survival (limit of viability) at bottom. Weeks and months numbered by gestation.

There is no sharp limit of development, age, or weight at which a fetus automatically becomes viable. [2] According to data years 2003-2005, 20 to 35 percent of babies born at 23 weeks of gestation survive, while 50 to 70 percent of babies born at 24 to 25 weeks, and more than 90 percent born at 26 to 27 weeks, survive.[3] It is rare for a baby weighing less than 500 gm to survive.[2]

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Limit of viability

The limit of viability is the gestational age at which a prematurely born fetus/infant has a 50% chance of longterm survival outside its mother's womb. With the support of neonatal intensive care units, the limit of viability in the developed world has declined since 50 years ago, but has remained unchanged in the last 12 years.[4][5] Currently the limit of viability is considered to be around 24 weeks although the incidence of major disabilities remains high at this point.[6][7] Neonatologists generally would not provide intensive care at 23 weeks, but would from 26 weeks.[8][9]

During the past several decades, neonatal care has improved with advances in medical science, and therefore the limit of viability has moved earlier.[10] As of 2006, the two youngest children to survive premature birth are thought to be James Elgin Gill (born on 20 May 1987 in Ottawa, Canada, at 21 weeks and 5 days gestational age), [11][12] and Amillia Taylor (born on 24 October 2006 in Miami, Florida, at 21 weeks and 6 days gestational age).[13][14] Both children were born just under 20 weeks from fertilization, or a few days past the midpoint of an average full-term pregnancy. Despite their premature births, both developed into healthy children.

The lower limit of viability is approximately five months gestational age, and usually later.[15]

Causes of death

When preterm babies are born, the main causes of perinatal mortality is that the respiratory system and the central nervous system are not completely differentiated,[2] causing infant respiratory distress syndrome. If given expert postnatal care, some fetuses weighing less than 500 gm may survive, being are referred to as extremely low birth weight or immature infants.[2] Preterm birth is the most common cause of perinatal mortality, causing almost 30 percent of neonatal deaths.[16]

See also

Footnotes

  1. ^ Houston Infertility Clinic--> Glossary By Dr. Sonja Kristiansen. Retrieved on September 11, 2009
  2. ^ a b c d e Moore, Keith and Persaud, T. The Developing Human: Clinically Oriented Embryology, p. 103 (Saunders 2003).
  3. ^ March of Dimes --> Neonatal Death Retrieved on September 2, 2009
  4. ^ Fergus Walsh (11 April 2008). "Prem baby survival rates revealed". BBC News. http://news.bbc.co.uk/1/hi/health/7340288.stm. Retrieved 2008-05-11.  
  5. ^ "Early baby survival 'unchanged'". BBC News. 9 May 2008. http://news.bbc.co.uk/1/hi/health/7390522.stm. Retrieved 2008-05-11.  
  6. ^ Kaempf JW, Tomlinson M, Arduza C, et al. (2006). "Medical staff guidelines for periviability pregnancy counseling and medical treatment of extremely premature infants". Pediatrics 117 (1): 22–9. doi:10.1542/peds.2004-2547. PMID 16396856. http://pediatrics.aappublications.org/cgi/content/full/117/1/22.   - in particular see TABLE 1 Survival and Neurologic Disability Rates Among Extremely Premature Infants
  7. ^ Morgan MA, Goldenberg RL, Schulkin J (2008). "Obstetrician-gynecologists' practices regarding preterm birth at the limit of viability". J. Matern. Fetal. Neonatal. Med. 21 (2): 115–21. doi:10.1080/14767050701866971. PMID 18240080.  
  8. ^ Vavasseur C, Foran A, Murphy JF (2007). "Consensus statements on the borderlands of neonatal viability: from uncertainty to grey areas". Ir Med J 100 (8): 561–4. PMID 17955714. "All would provide intensive care at 26 weeks and most would not at 23 weeks. The grey area is 24 and 25 weeks gestation. This group of infants constitute 2 per 1000 births.".  
  9. ^ Kaempf et al. (2006) Table of neonatologists rescussitation advice showing gestation ages at which they have neutral poistions whether they would or would not recommend rescussitation.
  10. ^ Roe v. Wade, 410 U.S. 113 (1973) ("viability is usually placed at about seven months (28 weeks) but may occur earlier, even at 24 weeks.") Retrieved 2007-03-04.
  11. ^ "Powell's Books - Guinness World Records 2004 (Guinness Book of Records) by". http://www.powells.com/biblio?show=0553587129&page=excerpt?. Retrieved 2007-11-28.  
  12. ^ "Miracle child". http://www.canada.com/topics/bodyandhealth/story.html?id=db8f33ab-33e9-429f-bedc-b6ca80f61bdc. Retrieved 2007-11-28.  
  13. ^ "Most-premature baby allowed home". BBC News. 2007-02-21. http://news.bbc.co.uk/1/hi/world/americas/6384621.stm. Retrieved 2007-05-05.  
  14. ^ Baptist Hospital of Miami, Fact Sheet (2006).
  15. ^ Halamek, Louis. "Prenatal Consultation at the Limits of Viability", NeoReviews, Vol.4 No.6 (2003): "most neonatologists would agree that survival of infants younger than approximately 22 to 23 weeks’ estimated gestational age [i.e. 20 to 21 weeks' estimated fertilization age] is universally dismal and that resuscitative efforts should not be undertaken when a neonate is born at this point in pregnancy."
  16. ^ March of Dimes --> Neonatal Death Retrieved on September 2, 2009

The limit of viability is the gestational age at which a prematurely born fetus/infant has a 50% chance of longterm survival outside its mother's womb. With the support of neonatal intensive care units, the limit of viability in the developed world has declined since 50 years ago, but has remained unchanged in the last 12 years.[1][2] Currently the limit of viability is considered to be around 24 weeks although the incidence of major disabilities remains high at this point.[3][4] Neonatologists generally would not provide intensive care at 23 weeks, but would from 26 weeks.[5][6]

Footnotes

  1. Fergus Walsh (11 April 2008). "Prem baby survival rates revealed". BBC News. http://news.bbc.co.uk/1/hi/health/7340288.stm. Retrieved on 2008-05-11. 
  2. "Early baby survival 'unchanged'". BBC News. 9 May 2008. http://news.bbc.co.uk/1/hi/health/7390522.stm. Retrieved on 2008-05-11. 
  3. Kaempf JW, Tomlinson M, Arduza C, et al. (2006). "Medical staff guidelines for periviability pregnancy counseling and medical treatment of extremely premature infants". Pediatrics 117 (1): 22–9. doi:10.1542/peds.2004-2547. PMID 16396856. http://pediatrics.aappublications.org/cgi/content/full/117/1/22.  - in particular see TABLE 1 Survival and Neurologic Disability Rates Among Extremely Premature Infants
  4. Morgan MA, Goldenberg RL, Schulkin J (2008). "Obstetrician-gynecologists' practices regarding preterm birth at the limit of viability". J. Matern. Fetal. Neonatal. Med. 21 (2): 115–21. doi:10.1080/14767050701866971. PMID 18240080. 
  5. Vavasseur C, Foran A, Murphy JF (2007). "Consensus statements on the borderlands of neonatal viability: from uncertainty to grey areas". Ir Med J 100 (8): 561–4. PMID 17955714. "All would provide intensive care at 26 weeks and most would not at 23 weeks. The grey area is 24 and 25 weeks gestation. This group of infants constitute 2 per 1000 births.". 
  6. Kaempf et al. (2006) Table of neonatologists rescussitation advice showing gestation ages at which they have neutral poistions whether they would or would not recommend rescussitation.

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