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Last Edited: 9/30/2010

Prematurity and Growth Retardation: Who is at Risk?

Different population groups in the United States and California experience different burdens of prematurity and growth retardation. Disparities in any health outcome sometimes provide clues regarding the causes of disease.  Perhaps more importantly, they enable us to understand patterns of health outcomes as social justice issues.

The ways in which we discuss these patterns are largely determined by the data sources that we have.  Birth certificate records contain two types of information that help us in this regard:  (a) mother’s racial and ethnic identification (although this may be recorded inconsistently), and (b) the location of the mother’s residence at the time of delivery.

Racial and ethnic disparities in California

As an example, among births in California in 2006, rates of preterm birth were:

Mother's race/ethnicity Preterm birth rate (%) 95% Confidence Interval
African-American 14.2 13.8 - 14.6
Asian 8.9 8.6 - 9.2
Filipina 12.4 11.9 - 13.0
Pacific Islander 11.8 10.6 - 13.1
Mexican-American 10.3 10.2 - 10.5
Central- and South-American 11.3 10.9 - 11.6
Native American 11.6 10.4 - 13.0
White 8.5 8.4 - 8.6


The causes of these disparities have yet to be explained. At least part of the pattern appears to be due to the effects of poverty on nutrition, stress, and access to health services. Some researchers have suggested a role for a "preterm birth gene", and physiological differences in maternal responses to inflammation between races have been noted.1-4   Others, however, have pointed out that the genetic heterogeneity of US populations makes it unlikely that genes could be responsible for such a persistent social pattern.5 


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Prematurity increases risk of infant mortality among African-Americans

Nationally, the rate of preterm births among African-American women is approximately double that among white women.  This disparity appears to be a major factor driving differences in infant mortality rates between these groups.6 Over time, the preterm disparity has narrowed slightly, as the rate for African-Americans has declined and that for whites has risen.  Severely preterm African-American infants tend to be sicker than their white counterparts, however, so the gap in infant mortality rates has not narrowed.7

Because of the size and persistence of black-white disparities in birth outcomes, the potential roles of discrimination and segregation are perhaps best studied for these groups. Some important findings to keep in mind include:

  • Women who report personal experiences with interpersonal racial discrimination are at higher risk of preterm birth or low birthweight than other women;8-10
  • "Neighborhood resources" appear to be important: low-income women living in comparatively wealthy communities have lower risks for preterm or low birthweight births than low-income women living in poor neighborhoods. Although this living situation (called "positive income incongruity") is not uncommon among low income white women, it is comparatively rare among black women;11-13
  • Women living in communities with strong social and familial ties are at lower risk for preterm or low birthweight birth than women who are relatively isolated;12-18
  • Infants of foreign-born black mothers are less likely to be preterm or low birthweight than those of black mothers native to the U.S.19,20 This pattern has been noted among several immigrant communities in addition to Africans (see below).


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The "Healthy Immigrant Effect" among some Hispanic/Latino groups

The ethnic category Hispanic/Latino contains people whose families may have come from a large variety of countries at varying times in the past and who have diverse life experiences. Nationwide, Puerto Rican mothers consistently have the highest rates of preterm birth and low birthweight among Hispanics.21 In many settings, other Hispanics experience rates of these outcomes near or below the nationwide average, but it has been noted that recent immigrants frequently (although not always) have better outcomes than those who are second- or third-generation Americans. It is unclear whether this "healthy immigrant effect" could be due to selection bias (healthier mothers are more able to immigrate), to maintenance of helpful social networks in other countries, or to poor nutrition and living conditions in the United States. Among immigrant communities from different countries, this pattern is most notable among Mexicans and (non-Hispanic) Asians.21


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Differences among Asian-American groups

Asian-Americans are a similarly diverse group with respect to their countries of origin, time in the United States, and circumstances under which they or their ancestors immigrated to the United States. Prematurity and low birthweight appear to be most common among South Asians (Indians), although less pronounced elevations have been noted in California among Cambodians, Laotians, Filipinas, and Thais.22,23


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Higher rates among Native Americans

Studies suggest that Native American infants are slightly larger than white infants, but their higher rate of preterm delivery means that low birthweight is more frequent.24-26 Infant mortality remains strikingly higher among Native Americans compared to the population in general, although this mortality tends to occur later during infancy due to causes such as SIDS, accidents, and infections, which are less directly associated with prematurity.27, 28


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What do our racial/ethnic categories really mean?

The concepts of race and ethnicity are very difficult to define. On one hand, the ways that human individuals are genetically different from each other are tiny compared to the ways in which they are similar, and few genetic traits have been found that fit into any of the categories commonly spoken of as race or ethnicity. On the other hand, we know that race and ethnicity have historically had profound impacts on individuals' biographies, opportunities, and experiences. The fact that we can use these categories--broad and imperfect though they are--to demonstrate disparities in health is testimony to the work that needs to be done to promote equitable access to resources and protection from potential causes of disease.

Although birth certificate records contain information about maternal and paternal race and ethnicity, we know that these data are not necessarily recorded consistently and may not reflect peoples' self identification, much less capture their experiences with respect to discrimination, acculturation, or vulnerability to health problems. When using information from this source, these limitations should be kept in mind.

Beyond these caveats, CEHTP personnel make the following distinctions when processing race/ethnicity data from birth certificate records:

Hispanics are classified based on the national origin of their families, even if they were born in the United States; as such they may be of any race.  Most Hispanics in California have family origins in either (a) Mexico or (b) Central or South America.  We therefore present data using these two categories of national origin.

Non-hispanics are generally reported using the following categories:

  • African-Americans
  • Asians and Asian-Americans, which include East, Southeast, and South Asians but not those of Philippine descent
  • Filipinas and Filipinos
  • Pacific Islanders, which includes Hawaiians, Guamanians, and Samoans
  • Native Americans, which includes Eskimos and Aleuts
  • Whites, who are generally of European ancestry

Finally, birth certificate records currently do not allow for the recording of race and ethnicity as combinations of these categories (that is, bi-racial or multi-ethnic individuals), so the experiences and identities of many more individuals are not completely represented.


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1. Menon R, Camargo M, Thorsen P, Lombardi S, Fortunato S. Amniotic fluid interleukin-6 increase is an indicator of spontaneous preterm birth in white but not black Americans. American Journal of Obstetrics and Gynecology. 2008;198:77.e71-77.e77.
2. Menon R, Thorsen P, Vogel I, et al. Racial disparity in amniotic fluid concentrations of tumor necrosis factor (TNF)-Éø and soluable TNF receptors in spontaneous preterm birth. American Journal of Obstetrics and Gynecology. 2008;198:533.e.531-533.e.510.
3. Menon R, Velez D, Thorsen P, et al. Ethnic differences in key candidate genes for spontaneous preterm birth: TNF-Éø and its receptors. Human Heredity. 2006;62:107-118.
4. Menon R, Williams S, Fortunato S. Amniotic fluid interleukin-1É¿ and interleukin-8 concentrations: Racial disparity in preterm birth. Reproductive Sciences. 2007;14:253-259.
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6.  Placeholder (reference 26)
7.  Placeholder (reference 27)
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