Birth weight

Birth weight is the body weight of a baby at its birth.

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.

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
 * 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
 * Environmental factors, including exposure of the mother to secondhand smoke
 * Economic status of the parents gives inconsistent study findings according to a review on 2010, and remains speculative as a determinant.
 * Other factors, like multiple births, where each baby is likely to be outside the AGA, 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, but it was also shown that this relationship is fully explained by maternal weight.

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.

Diabetes
Babies that have a low birth weight are thought to have an increased risk of developing type 2 diabetes in later life.

Intelligence
Some studies have shown a direct link between an increased birth weight and an increased intelligence quotient. Increased birth weight is also linked to greater risk of developing autism.