Low-birth-weight risk and mother's nativity status: associations vary by race, ethnicity and education.

Immigrant women are less likely than U.S. natives to have a low-birth-weight baby, but analyses of national data show that the association varies by race or ethnicity and by educational level. (1) Overall, immigrants who gave birth in 1998 had 15% lower odds than U.S.-born women of having a low-birth-weight baby. The odds were reduced for foreign-born black and Hispanic women, but were elevated for Asian immigrants; among white women, nativity status was not associated with the likelihood of having a low-birth-weight baby. White, black and Hispanic immigrants with fewer than 12 years of schooling were less likely than their native-born counterparts to have a low-birth-weight baby, but findings were inconsistent among better educated women.

The analyses, based on data from the Detail Natality Set, included more than two million singleton births to women aged 20 and older, of whom 68% were white, 15% black, 3% Asian and 14% Hispanic. In addition to maternal nativity status, race, ethnicity and education, the data set provides information on behavioral and medical factors that could increase women's risk of having a baby who is low-birth-weight (defined as less than 2,500 g). In a series of logistic regressions controlling for these factors, the analysts examined relationships between nativity status and low birth weight, paying particular attention to whether associations varied across racial and ethnic groups and by socioeconomic status (as indicated by mother's level of education).

In each racial and ethnic group, infants were about evenly divided between males and females; most were born to women who had given birth before. Nine in 10 mothers in each group were younger than 35. The majority of white and Asian mothers had had more than 12 years of schooling, and the majority of blacks and Hispanics had had a high school education or less.

Behavioral and medical risk factors varied by race and ethnicity. For example, the proportion of women who had received adequate prenatal care was about two-thirds among black and Hispanic women, three-quarters among Asians and eight in 10 among whites. Nine in 10 whites and Asians were married, compared with two-thirds of Hispanics and four in 10 blacks. Levels of smoking and drinking were lower among Asian and Hispanic mothers than among white and black women. While the proportions of women with chronic hypertension and anemia were highest among black mothers, the proportion with diabetes was highest among Asians.

Overall, 5% of white and Hispanic women, 6% of Asians and 11% of blacks had a low-birth-weight baby. The proportion was greater among foreign-born Asian women than among their native-born counterparts, but the relationship was reversed for the other racial and ethnic groups. Reductions for blacks and Hispanics were particularly striking (about 30% and 20%, respectively).

Findings from the first set of multivariate analyses revealed that black, Asian and Hispanic women were significantly more likely than white women to have a low-birth-weight baby (odds ratios, 2.4, 1.8 and 1.3, respectively) and that the odds of this outcome were 15% lower for immigrants than for women born in the United States. Foreign-born black and Hispanic women had 23% lower odds than their U.S.-born counterparts of having a low-birth-weight baby. For Asians, however, the odds were elevated by 29% among immigrants, and for whites, nativity status was not significantly associated with the likelihood that a baby was low-birth-weight.

When the analyses were stratified by race or ethnicity, findings regarding nativity status were similar to those in the initial analyses. Furthermore, across racial or ethnic groups, women generally had an elevated likelihood of bearing a low-birth-weight baby if they were 35 or older, were unmarried, had not received adequate prenatal care and smoked or drank during pregnancy. Their risk increased if they had had chronic hypertension, preeclampsia or eclampsia, or placental bleeding disorders. Findings with regard to education varied among racial and ethnic groups: For white women, the risk of low birth weight rose steadily as educational attainment declined (odds ratio, 1.6 for those with less than a high school education); the same was true for black women, although the increase was less dramatic (1.3 for the least educated women). For Asians and Hispanics, the association was weaker and less consistent.

The final set of analyses examined whether associations with nativity status varied by race or ethnicity and education. Results showed that for black women, the reduction in the likelihood of having a low-birth-weight baby associated with being foreign-born diminished steadily as level of education increased. For example, the least educated black immigrants had a 36% lower risk than their U.S.-born counterparts; the best educated, a 20% reduction in risk. Results for Hispanics were similar: Immigrants' risk was reduced more among those with less than a high school education than among those who had completed high school (29% and 17%, respectively), but it was not reduced among women with postsecondary education. No clear pattern was apparent for Asian women; the risk of low birth weight was elevated only for immigrants with 13-15 years of schooling (odds ratio, 1.5). Foreign-born white women with less than a high school education had an 18% lower risk than their U.S.-born counterparts, but no associations were significant for better-educated women. Within racial or ethnic groups, associations were stronger for women born in the United States than for immigrants.

The analysts acknowledge that the data do not allow them to assess the mechanisms accounting for variations in low birth weight by race, ethnicity, nativity and education. Additionally, because education was the only available measure of socioeconomic status, they could not determine whether other socioeconomic characteristics influenced their results. For researchers to better understand low-birth-weight disparities among racial and ethnic groups, the analysts conclude, it will be necessary to explore such issues as the health status of immigrants, cultural factors, social support and socioeconomic context.

REFERENCE

(1.) Acevedo-Garcia D, Soobader M-J and Berkman LF, The differential effect of foreign-born status on low birth weight by race/ethnicity and education, Pediatrics, 2005, 115(1):e20-e30, <www.pediatrics.org/cgi/doi/10.1542/ peds.2004-1306>, accessed Jan. 20, 2005.