Birth Outcomes
What Is It?
Birth outcomes are a category of measures that describe the health of babies at birth. These outcomes, such as low birth weight (LBW), represent a child’s current and future morbidity — or whether a child has a “healthy start” — and serve as a health outcome related to maternal health risk.
Why Do We Measure It?
LBW is unique as a health outcome because it represents two factors: maternal exposure to health risks and the infant’s current and future morbidity, as well as premature mortality risk. The health associations and impacts of LBW are numerous.
From the perspective of maternal health outcomes, LBW indicates maternal exposure to health risks in all categories of health factors, including her health behaviors, access to health care, the social and economic environment the mother inhabits, and environmental risks to which she is exposed. Bailey et al. find that modifiable maternal health behaviors — including weight gain, smoking, and alcohol and substance use — account for more than 10% of the variation in birth weight. Maternal smoking alone accounts for 7% of variation in birth weight.[1] Bergsjo and Villar’s systematic review of the evidence also finds that maternal nutrition, smoking, and excessive alcohol intake result in LBW.[2]
A systematic literature review of the effect of socioeconomic status disparities found that income inequality is associated with both infant mortality rates and LBW.[3] Neighborhood socioeconomic status and social climate were shown to have small to moderate effects on child health outcomes, i.e. birth weight, injuries, behavioral problems, and child maltreatment.[4] On average, 10% of variation in child health outcomes (including birth weight) was explained by neighborhood determinants, after controlling for important individual and family variables.[4] A recent review of the effect of air pollution on children’s health argues that ambient air quality can affect birth outcomes.[5] Two other systematic reviews find that while air pollution demonstrated an association with intrauterine growth retardation and pre-term delivery (factors linked to LBW), it did not always show a significant association with LBW itself.[6-7]
In terms of the infant’s health outcomes, LBW serves as a predictor of premature mortality and/or morbidity over the life course.[8] Gestational age, which is correlated with birth weight, is inversely related to psychological distress.[9] LBW children have greater developmental and growth problems, are at higher risk of cardiovascular disease later in life, and have a greater rate of respiratory conditions.[10-13] In a systematic review, Whincup et al. found that LBW was associated with an elevated risk of developing type 2 diabetes.[14]
LBW has also been associated with cognitive development problems. Several authors find that LBW children have higher rates of sensorineural impairments, such as cerebral palsy, and visual, auditory, and intellectual impairments.[10-12,15-17] However, Shenkin finds that parental social class accounted for a greater proportion of the variance in cognitive ability and the two variables were independent.[15] Very preterm infants have lower median IQ scores at age 6, and they have global learning deficits compared to their peers.[18] As a consequence, preterm birth and LBW can “impose a substantial burden on special education and social services, on families and caretakers of the infants, and on society generally.”[19]
Measurement Strategies
The concept of a “healthy start,” as well as an outcome of maternal health risk, can easily be measured through three correlated indicators:
- Low birth weight (less than 2,500 g)
- Very low birth weight (less than 1,500 g)
- Gestational age
What Is the County Health Rankings Measurement Strategy?
The County Health Rankings uses the measure of low birth weight (less than 2,500 g) calculated from data in from the National Vital Statistics System and provided by the CDC’s National Center for Health Statistics.
Measure Strengths & Limitations
Health risks are greater for very low birth weight babies but low birth weight is preferred to very low birth weight in the County Health Rankings because it is a more common event which in turn allows for better data coverage; infants born below 2500 grams also face increased risk of morbidity and premature mortality. Although gestational age may be a better measure than low birth weight as it better accounts for a child’s neurological and physical development at birth, gestational age can be difficult to ascertain, whereas birth weight is easily measured and reported. Additionally, a measure of gestational age aggregated to the county level would be difficult to interpret.
References
[1] Bailey BA, Byrom AR. Factors predicting birth weight in a low-risk sample: The role of modifiable pregnancy health behaviors. Matern Child Health J. 2007;11:173-179.
[2] Bergsjo P, Villar J. Scientific basis for the content of routine antenatal care. Acta Obstet Gynecol Scand. 1997;76:15-25.
[3] Spencer N. The effect of income inequality and macro-level social policy on infant mortality and low birth weight in developed countries: A preliminary systematic review. Child Care Health Dev. 2004;30:699-709.
[4] Sellstrom E, Bremberg S. The significance of neighbourhood context to child and adolescent health and well-being: A systematic review of multilevel studies. Scand J Public Health. 2006;34:544-554.
[5] Koranteng S, Vargas ARO, Buka I. Ambient air pollution and children's health: A systematic review of Canadian epidemiological studies. Paediatr Child Health. 2007;12:225-233.
[6] Maisonet M, Correa A, Misra D, Jaakkola JJK. A review of the literature on the effects of ambient air pollution on fetal growth. Environ Res. 2004;95:106-115.
[7] Glinianaia SV, Rankin J, Bell R, Pless-Mulloli T, Howel D. Particulate air pollution and fetal health a systematic review of the epidemiologic evidence. Epidemiology. 2004;15:36-45.
[8] Paneth NS. The problem of low birth weight. Future Child. 1995;5:19-34.
[9] Cheung YB. Early origins and adult correlates of psychosomatic distress. Soc Sci Med. 2002;55:937-948.
[10] Knoches AML, Doyle LW. Long-term outcome of infants born preterm. Baillieres Clin Obstet Gynaecol. 1993;7:633-651.
[11] Hack M, Klein N, Gerry Taylor H. School-age outcomes of children of extremely low birth weight and gestational age. Semin Neonatol. 1996;1:277-288.
[12] Hack M, Klein NK, Taylor HG. Long-term developmental outcomes of low birth weight infants. Future Child. 1995;5:176-196.
[13] Irving RJ, Belton NR, Elton RA, Walker BR. Adult cardiovascular risk factors in premature babies. Lancet. 2000;355:2135-2136.
[14] Whincup PH, Kaye SJ, Owen CG, et al. Birth weight and risk of type 2 diabetes: A systematic review. JAMA. 2008;300:2886-2897.
[15] Shenkin SD, Starr JM, Deary IJ. Birth weight and cognitive ability in childhood: A systematic review. Psychol Bull.130:989-1013.
[16] Reichman NE. Low birth weight and school readiness. Future Child. 2005;15:91-116.
[17] Saigal S, Doyle LW. An overview of mortality and sequelae of preterm birth from infancy to adulthood. Lancet. 2008;371:261-269.
[18] Jobe AH. Outcomes for children born at 25 weeks gestation or less. J Pediatr. 2008;152:A2.
[19] Petrou S, Petrou S, Sach T, Davidson L. The long-term costs of preterm birth and low birth weight: Results of a systematic review. Child Care Health Dev. 2001;27:97-115.
