The Future of Children, Princeton - Brookings: Providing research and analysis to promote effective policies and programs for children.

Socioeconomic status and race/ethnicity are indicators of complex linkages among environmental events, psychological states, and physiologic factors which may lead to low birth weight or preterm delivery. While we do not fully understand the specific biological pathways responsible, we do know that a woman's social and economic status will influence her general health and access to resources. (See the article by Hughes and Simpson in this journal issue for a detailed analysis of the effects of social factors on low birth weight.) In this section, we review the effects of some demographic indicators.

Socioeconomic Status

Low birth weight and infant mortality are closely related to socioeconomic disadvantage. Socioeconomic status, however, is difficult to measure accurately. Educational attainment, marital status, maternal age, and income are interrelated factors and are often used to approximate socioeconomic status, but no single factor truly measures its underlying influence.

Maternal education, maternal age, and marital status are all reflective of socioeconomic status and predictive of low birth weight. Twenty-four percent of the births in 1989 were to women with less than a high school education.¹ Low educational attainment is associated with higher rates of low birth weight.² For example, relative to college graduates, white women with less than a high school education were 50% more likely to have babies with very low birth weight (less than 1,500 grams, or 3 pounds, 5 ounces) and more than twice as likely to have babies with moderately low birth weight (between 1,500 grams and 2,500 grams, or 3 pounds, 5 ounces and 5 pounds, 8 ounces) than were women who graduated from college.² Teenage mothers are at greater risk of having a low birth weight baby than are mothers aged 25 to 34.¹ However, it is not clear if the risk of teenage childbearing is due to young maternal age or to the low socioeconomic status that often accompanies teenage pregnancy.

The marital status of the mother also appears to be independently associated with the rate of low birth weight,^2,3 although the relationship appears to vary by maternal age and race. The association of unmarried status with low birth weight is probably strongest for white women over 20 years of age.^2,4 Marital status may also serve as a marker for the "wantedness" of the child, the economic status of the mother, and the social support that the mother has—all of which are factors that may influence the health of the mother and infant.

It has been hypothesized that economic disadvantage may be a risk factor for low birth weight partly because of the high levels of stress and negative life events that are associated with being poor. Both physical stress and fatigue—particularly related to work during pregnancy—and psychological distress have been implicated.⁵ In addition, stress and negative life events are associated with health behaviors such as smoking.⁶ Social support may act as a moderator or as a buffer from the untoward effects of stressful life experiences and emotional dysfunction.⁷

Race/Ethnicity

The prevalence of low birth weight among white infants is less than half of that for African-American infants (6% and 13%, respectively). This difference reflects a twofold increase of preterm and low birth weight births among African-American mothers.¹ African-American mothers are more likely to have less education, not to be married, and to be younger than white mothers.¹ However, at almost all educational levels and age categories, African-American women have about double the rates of low birth weight as white women.⁸ This fact indicates that these demographic differences in education, marital status, and age do not account for the large disparity between African Americans and whites in the incidence of low birth weight.

Among infants of Hispanic origin, who represented approximately 15% of live births in 1989, the rate of low birth weight was relatively low (6.1% overall), particularly given that Hispanic women (except Cuban women) had limited educational attainment and were not as likely as non-Hispanic white women to receive prenatal care early in pregnancy.¹

However, Hispanics are a very diverse group, and the low birth weight rates vary considerably by national origin. Low birth weight rates range from 9.4% among Puerto Rican mothers to 5.6% among Cuban mothers. Among Asian infants in 1989, the incidence of low birth weight ranged from 5.1% for Chinese births to 7.3% for Filipino births.¹

It is not known why infants of African-American mothers are twice as likely as all other infants to be born with low birth weights. The etiology of racial disparities in infant mortality and low birth weight is probably multifactorial in nature and is not completely explained by differences in demographics, use of tobacco and other drugs, or medical illnesses.⁹ During the primary childbearing years (ages 15 to 29), the general mortality of African-American women exceeds that of white women for virtually every cause of death.

African-American women have higher rates of hypertension, anemia, and low-level lead exposure than other groups,¹⁰ suggesting that the general health status of African-American women may be suboptimal. Infants of African-American foreign-born mothers have lower risks of neonatal mortality than infants of African-American U.S.–born mothers, a relationship that is not seen between foreign- and U.S.–born white women.¹¹ In addition, racial or ethnic differences in familial structure and social networks may affect morbidity and mortality.¹² More research will be needed to clarify the reasons for these disparities.