Risk Factors for Low Birth Weight

Low birth weight is defined by the WHO as an infant weighing less than 5 pounds 8 ounces.  It’s a significant predictor of infant mortality in the first week of life, as well as other negative consequences; low-birth-weight children do worse in school and tests[1] by about half a standard deviation [2] and have more problems with attention and executive function.  Low-birth-weight infants also grow up to be slightly more likely to be overweight, have hypertension, and have diabetes.[3][4]

The CDC estimates that 8% of American babies are low-birth-weight.[5]  This is fairly high, for developed countries; only 4% of Finnish or Korean babies are low-birth-weight. [6]  Low birthweight is responsible for about a third of the US’s higher infant mortality than Europe’s.

So, what causes low birthweight?

There are two types of low birthweight: prematurity, and intrauterine growth restriction (or low birthweight for gestational age.)   IUGR infants are far more likely to have stunted growth later in life.  Premature infants are more likely to have dangerous diseases of infancy such as infant respiratory distress syndrome (one of the top causes of infant mortality).[7]

Intrauterine growth retardation can be caused by multiple factors, including chromosomal abnormalities in the fetus (about 20% of IUGR infants), maternal vascular disease which starves the fetus of nutrients (about 20-35% of IUGR infants) and maternal malnutrition.  So we should expect the risk factors for birth defects and miscarriage to also be risk factors for low birthweight.[12]

Low Weight

Gaining less than 15 pounds during pregnancy was associated with an odds ratio of low birth weight of 3.38 for preterm births and 4.08 for full-term births.[8]  Being underweight before pregnancy was associated with an odds ratio of 2.36 of small-for-gestational-age infants.[13]

Spousal Abuse

Being abused by one’s partner was associated with an odds ratio of low birth weight of 3.29 for physical abuse and 3.78 for nonphysical abuse.[8]  A meta-analysis gives an odds ratio of 1.4 for any abuse during pregnancy.[9]

Diabetes

Pregestational diabetes was associated with an odds ratio of 3.3 for intrauterine growth restriction.

Poor education

Not finishing high school was associated with an odds ratio of 2.69 of intrauterine growth restriction.[11]

Social Isolation

“Never or seldom meets friends” was associated with an odds ratio of 2.42 of intrauterine growth restriction and an odds ratio of 1.20 of prematurity.  This effect persisted even after adjusting for maternal education.[11]

Smoking 

Smoking was associated with an odds ratio of 2.28 for low birthweight in full-term births.[9]

 

Basically, to the extent that we can separate low birthweight from prematurity, it still has a lot of the same risk factors. Low socioeconomic status and the things that correlate with it; diabetes; smoking; low weight.

References

[1]Weindrich, Diana, Manfred Laucht, and Martin H. Schmidt. “Late sequelae of low birth weight: mediators of poor school performance at 11 years.”Developmental Medicine & Child Neurology 45.7 (2003): 463-469.

[2]Aarnoudse-Moens, Cornelieke Sandrine Hanan, et al. “Meta-analysis of neurobehavioral outcomes in very preterm and/or very low birth weight children.” Pediatrics 124.2 (2009): 717-728.

[3]Curhan, Gary C., et al. “Birth weight and adult hypertension, diabetes mellitus, and obesity in US men.” Circulation 94.12 (1996): 3246-3250.

[4]Rich-Edwards, Janet W., et al. “Birth weight and risk of cardiovascular disease in a cohort of women followed up since 1976.” Bmj 315.7105 (1997): 396-400.

[5]http://www.cdc.gov/nchs/fastats/birthweight.htm

[6]http://www.unicef.org/publications/files/low_birthweight_from_EY.pdf

[7]Kramer, Michael S. “Determinants of low birth weight: methodological assessment and meta-analysis.” Bulletin of the World Health Organization65.5 (1987): 663.

[8]Campbell, Jacquelyn, et al. “Physical and nonphysical partner abuse and other risk factors for low birth weight among full term and preterm babies a multiethnic case-control study.” American Journal of Epidemiology 150.7 (1999): 714-726.

[9]Campbell, Jacquelyn, et al. “Physical and nonphysical partner abuse and other risk factors for low birth weight among full term and preterm babies a multiethnic case-control study.” American Journal of Epidemiology 150.7 (1999): 714-726.

[10]Murphy, Claire C., et al. “Abuse: a risk factor for low birth weight? A systematic review and meta-analysis.” Canadian Medical Association Journal164.11 (2001): 1567-1572.

[11]Nordentoft, Merete, et al. “Intrauterine growth retardation and premature delivery: the influence of maternal smoking and psychosocial factors.”American Journal of Public Health 86.3 (1996): 347-354.

[12]Resnik, Robert. “Intrauterine growth restriction.” Obstetrics & Gynecology99.3 (2002): 490-496.

[13]Abrams, Barbara, and Vicky Newman. “Small-for-gestational-age birth: maternal predictors and comparison with risk factors of spontaneous preterm delivery in the same cohort.” American journal of obstetrics and gynecology164.3 (1991): 785-790.

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