Birth weight

Baby weighed as appropriate for gestational age.

Birth weight is the body weight of a baby at its birth.^[1] The average birth weight in babies of European heritage is 3.5 kilograms (7.7 lb), though the range of normal is between 2.5 kilograms (5.5 lb) and 5 kilograms (11 lb) (all but 5% of newborns will fall into this range). Babies of south Asian and Chinese heritage weigh about 240 grams (0.53 lb) less.^[2][3]

There have been numerous studies that have attempted, with varying degrees of success, to show links between birth weight and later-life conditions, including diabetes, obesity, tobacco smoking and intelligence. Low birth weight is associated with neonatal infection.

Determinants

There are basically two distinct determinants for birth weight:

• The duration of gestation prior to birth, that is, the gestational age at which the child is born

Relation of weight and gestational age.

• The prenatal growth rate, generally measured in relation to what weight is expected for any gestational age.

The incidence of birth weight being outside what is normal is influenced by the parents in numerous ways, including:

• Genetics
• The health of the mother, particularly during the pregnancy. Intercurrent diseases in pregnancy are sometimes associated with decreased birth weight. For example, Celiac disease confers an odds ratio of low birth weight of approximately 1.8.^[4]
• Environmental factors, including exposure of the mother to secondhand smoke^[5]
• Economic status of the parents gives inconsistent study findings according to a review on 2010, and remains speculative as a determinant.^[6]
• Other factors, like multiple births, where each baby is likely to be outside the AGA (appropriate for gestational age), one more so than the other.

Abnormalities

• A low birth weight can be caused either by a preterm birth (low gestational age at birth) or of the infant being small for gestational age (slow prenatal growth rate), or a combination of both.
• A very large birth weight is usually caused by the infant having been large for gestational age

Influence on adult life

Studies have been conducted to investigate how a person's birth weight can influence aspects of their future life. This includes theorised links with obesity, diabetes and intelligence.

Obesity

A baby born small or large for gestational age (either of the two extremes) is thought to have an increased risk of obesity in later life,^[7][8] but it was also shown that this relationship is fully explained by maternal weight.^[9]

GH therapy at a certain dose induced catch-up of lean body mass (LBM). However percentage body fat decreased in the GH-treated subjects. Bone mineral density SDS measured by DEXA increased significantly in the GH-treated group compared to the untreated subjects, though there is much debate over whether or not SGA (small for gestational age) is significantly adverse to children to warrant inducing catch-up.^[10]

Diabetes

Babies that have a low birth weight are thought to have an increased risk of developing type 2 diabetes in later life.^{[11][12][13] [14]}

Intelligence

Some studies have shown a direct link between an increased birth weight and an increased intelligence quotient.^[15][16][17] Increased birth weight is also linked to greater risk of developing autism.^[18]

Poor Neonatal Care

Recent evidence suggests that the effects of low birth weight are constant across developmental years, suggesting that poor neonatal care has long term impacts.^[19]

Epidemiology

Disability-adjusted life years out of 100,000 lost due to any cause in 2004.^[20]

  no data

  less than 9,250

  9,250–16,000

  16,000–22,750

  22,750–29,500

  29,500–36,250

  36,250–43,000

  43,000–49,750

  49,750–56,500

  56,500–63,250

  63,250–70,000

  70,000–80,000

  more than 80,000

See also

• Barker's hypothesis
• MOMO syndrome
• Low birth weight paradox
• Prenatal nutrition and birth weight

References

External links

• MedlinePlus Encyclopedia Intrauterine growth restriction
• Peleg D, Kennedy CM, Hunter SK (August 1998). "Intrauterine growth restriction: identification and management". Am Fam Physician. 58 (2): 453–60, 466–7. PMID 9713399. 
• "Intrauterine growth restriction (IUGR)" at Health System, University of Virginia
• Fetal Growth Restriction at eMedicine
• "Researchers link low birth weight to lower achievement"
• "Management of Suspected Fetal Macrosomia"
• "Vit D linked to baby birth weight" at BBC News, 25 April 2006
• Born in Bradford - 2006 cohort study into the causes of low birth weight and infant mortality in Bradford, UK
• Intrauterine Growth Restriction Help - IUGR factors and solutions
• Walid MS, Astafyeva OV, Pomortsev AV (December 2007). "The IUGR prognostic scale". Arch Gynecol Obstet. 276 (6): 633–40. doi:10.1007/s00404-007-0398-1. PMID 17619893.