Infant Mortality and Birth Weight

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Infant Mortality and Birth Weight






Infant mortality refers to the death rate of babies less than one year old; it is expressed as the number who die per every thousand live births. The chances of dying are high among infants because they have not developed immunities to most infectious, parasitic, and communicable diseases, which are often associated with poor sanitary conditions and malnourishment. The infant mortality rate can thus be used as a gauge of the health of populations within and across countries.


The infant mortality rate (IMR) tends to decline as countries become more economically developed. For example, the IMR in the United States was about 100 per thousand live births in 1900, but in the early twenty-first century it is below 10 per thousand. Many countries have even lower rates than the United States, such as Japan (3.0), Finland (3.1), and Norway (3.4). In industrialized countries, differences in IMRs tend to be the result of disparities in the health status of women before and during pregnancy, as well as a reflection of the quality and accessibility of primary care for pregnant women and their infants. The IMRs for Peru (43), India (60), Laos (87), Ethiopia (116), Afghanistan (150), and Burundi (157) are very high, although most of these countries have witnessed a substantial decline in infant mortality since the 1960s (United Nations 2004). For example, the IMR in India was 146 in 1960 but reached a low of 60 in 2003. Nonetheless, many developing countries will continue to struggle in their efforts to eliminate adverse birth outcomes if they do not improve access to adequate health care facilities, improve the standards of living for all of their citizens, and put forth a more conscious effort at improving the health of women and children overall.

On a more positive note, the IMR has declined significantly around the world: It was 198 in 1960, 83 in 2001, and 54 in 2003. In the early 2000s, the most common causes of infant mortality worldwide are pneumonia and dehydration from diarrhea. The rate of children dying from dehydration is decreasing, however, due to the success of international efforts in providing mothers with information about Oral Rehydration Solution.


In the United States, the IMR has also steadily declined. It was 26.0 in 1960, but has dropped significantly, falling to 6.9 in 2000 (Iyasu and Tomashek 2000). A variety of factors have been proposed to explain the declining IMR across several different historical time periods in the United States. For example, in the early 1900s improved environmental and living conditions were responsible for initial declines in infant mortality, while the next few decades saw declines as a result of programs established to care for pregnant women and their infants (Meckel 1990). According to some scholars, infant mortality declined in the 1990s because of decreases in sudden infant death syndrome (SIDS) (Willinger 1998).

Although the United States has greatly reduced its IMR since the 1960s, it ranked only twenty-sixth among industrialized countries in infant mortality in 1999 (United Nations 2002). This ranking is in large part the result of disparities that continue to exist among various racial/ethnic groups in the United States, particularly between African Americans and whites. In 2000, infant mortality occurred at a rate of 14.0 per thousand live births among African Americans, compared to 5.7 for non-Hispanic whites (Iyasu and Tomashek 2000). By 2002 the IMR for African Americans had declined slightly to 13.9, but this was still more than double the rate of 5.8 for non-Hispanic whites. Infants of Native American (8.6) and Puerto Rican (8.2) mothers also have relatively high IMRs, while other ethnic groups in the United States, such as Mexicans (5.4), Japanese (4.9), Cubans (3.7), and Chinese (3.0), have relatively low IMRs (Mathews, Menacker, MacDorman 2002). Even though the infant mortality rate has declined throughout the twentieth century for all women, the comparative inconsistency between African Americans and whites remains unchanged.


Low birth weight is an important determinant of racial/ethnic differences in infant mortality in the United States. Low-birth-weight (LBW) babies are newborns weighing less than 2,500 grams (5 pounds 8 ounces) and very-low-birth-weight (VLBW) include newborns weighing less than 1,500 grams (3 pounds 4 ounces). The IMR for low-birth-weight infants is more than twenty times that of infants born at a normal weight (MacDorman and Atkinson 1999), putting them at a much greater risk for mortality.

In 2001 the percentage of LBW babies born to African-American mothers was 13.0. Although this figure represents a decline from a high of 13.6 in 1991, it is still considerably higher than the rate for Asian/Pacific Islander (7.5), American Indian (7.3), white (6.7), and Hispanic (6.5) births (Martin et al. 2003). In 2001 the rate of VLBW newborns remained at 1.4 percent of live births to U.S. women, but the rate of VLBW among African-American babies was more than two-and-a-half times higher than that among non-Hispanic whites (Martin et al. 2003). The black-white gap in infant mortality in the United States can be explained when adverse birth outcomes such as low birth weight are taken into account (Hummer et al. 1999).

According to the U.S. Centers for Disease Control and Prevention (CDC), other major contributors to infant mortality include congenital abnormalities, SIDS, and respiratory distress syndrome. In fact, SIDS rates are 2.4 times higher for African American babies and 2.6 times higher for Native American and Alaska Native babies than for non-Hispanic white babies.


Some relevant lifestyle factors influencing the likelihood of having a LBW infant are maternal smoking, drug and alcohol abuse, poor nutrition, and insufficient prenatal care. For example, in 2001 there was a higher percentage of LBW infants born to smokers (11.9 percent) than to nonsmokers (7.3 percent), a pattern that has been observed among both African American and white infants. Other factors associated with increased risk of LBW include maternal poverty, low levels of educational attainment, and family medical history (Conley and Bennett 2001).

Social scientists have developed a number of theories to help explain the high infant mortality rate among African Americans.

The Weathering Hypothesis. Arline Geronimus argues that there is a more rapid decline in the reproductive health of African-American women than in other women in the United States. According to Geronimus, this partially explains why older African-American women (those in their mid-twenties) have higher neonatal mortality rates (IMR for babies younger than 28 days) and a higher risk for having a LBW baby than their younger counterparts. In her research, Geronimus has found the opposite pattern for non-Hispanic white women, who have the lowest neonatal mortality rates and LBWs among women in their mid-twenties. According to this view, “weathering” occurs among African-American women as a result of a lifetime of exposure to economic disadvantage, untreated health conditions, accumulated obligations to significant others, negative health behaviors, limited job choices, and racial/ethnic discrimination.

Additional empirical support for the weathering hypothesis is mixed, however. Elizabeth Wildsmith (2002) has found some evidence for the hypothesis among U.S.-born Mexican–American women in terms of maternal health. Narayan Sastry and Jon Hussey (2003), using data from birth records of mothers who resided in Chicago, report that an increase in age is associated with a decrease in birth weight among African Americans, but with an increase in birth weight among Hispanics of Mexican origin. Michael Klitsch (2003), on the other hand, reports few racial/ethnic differences in the general pattern of decreasing infant death rates with increasing maternal age in a study of African-American, white, and Mexican-American women.

Cumulative Disadvantage. The weathering hypothesis is consistent with the “cumulative disadvantage” perspective that is often proposed to explain disparities in physical health between elderly minorities and their white peers (Crystal and Shea 1990). Those who embrace the cumulative disadvantage perspective argue that individuals who start out with fewer resources will have poorer health outcomes across the life course. Within the weathering framework, age is a resource that decreases in value over time more rapidly for African Americans than for non-Hispanic whites. Age brings with it certain forms of capital such as high energy and a sense of optimism. These resources are higher among the young compared to the old. The difference between these two perspectives, however, is that the weathering hypothesis is multiplicative (it includes the interaction between age and race/ethnicity) while the cumulative disadvantage view is additive (it includes only the linear effect of age and race/ethnicity). These perspectives emphasize the complex etiology of racial/ethnic differences in infant mortality rates.

The Intersectionality Hypothesis. A second view of disadvantage, referred to as the “intersectionality hypothesis,” also advocates a nonlinear relationship between race/ethnicity and health across groups (Mullings and Wali 2001; Weber and Parra-Medina 2003). This view suggests that a unique set of circumstances are created at the intersection of race, class, and gender that do not always support expectations. For example, African-American women who have graduated college have a higher infant mortality rate than white women who have not completed high school (Pamuk et al. 1998). Intersectionality theory provides a useful lens through which such health disparities may be more clearly viewed. In particular, attention is paid to the resources that are available to individuals as a result of the amount of power afforded to their group. It can be argued that African-American professional women must often navigate within the boundaries of organizations that are structured by both racial and gender divisions. In this case, it seems that middle-class status is experienced in a less profound and beneficial way for these women than for any other group. As a result, these women are not afforded the opportunity to organize resources that should be available to them given their social-class standing (Jackson and Williams 2005).

These perspectives are not contradictory. They simply draw attention to the accumulation of risk factors that produce disparities in IMRs. Many social scientists acknowledge the role that more general structures, such as residential segregation and neighborhood quality, play in producing racial disparities in health (Williams and Collins 2001). Residential segregation is directly associated with access to and quality of health care, as well as environmental hazards. In fact, because of segregation, middle-class African Americans live in poorer areas than do whites of similar economic status, and poor whites live in much better neighborhoods than do poor African Americans (Massey and Denton 1993). Predominantly African-American neighborhoods also have fewer quality health facilities (Williams and Jackson 2005), and their residents are more likely to be victims of environmental racism (Sexton et al. 1993). A related body of research highlights the role played by neighborhood disadvantage. Neighborhoods perceived as unsafe discourage residents from engaging in healthful behaviors such as walking (Ross and Mirowsky 2001). African-American babies born in more segregated cities have higher rates of infant mortality than those born in less segregated cities (Hogue and Hargraves 1993). A host of environmental and neighborhood-level factors are also associated with the risk of delivering a low-birth-weight baby (Sastry and Hussey 2003). Thus, residential segregation and other environmental factors play an important role in access to quality healthcare, the promotion of healthful behaviors during pregnancy, and resulting infant mortality rates.

The steady decline in infant mortality worldwide is an encouraging pattern for the future. It will be important, however, for scientists to continue to investigate a variety of factors (social, economic, environmental, biological) that contribute to infant deaths. On the other hand, some of the complex patterns found in racial/ethnic differences in infant mortality rates suggest that a concerted effort must also be made to carefully distinguish between these causes. For example, infant mortality rates among African Americans compared to non-Hispanic whites are primarily due to the higher incidence of LBW and preterm births. Similarly, Puerto Rican infants have higher IMRs because of higher LBW rates. On the other hand, the differential in the rate of SIDs helps explain the higher death rate among American Indian infants. Health officials must continue to document the causes of infant death, monitor the success of public health campaigns, and keep track of the increasing use of medical technologies, which can also help explain fluctuations in the infant mortality rate (Reuwer, Sijmans, and Rietman 1987; Zhang, Yancey, and Henderson 2002).

SEE ALSO Life Expectancy.


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Pamela Braboy Jackson
Yasmiyn Irizarry