While the path to obesity begins before birth, the earliest physical measurements of that path are made at birth. Data on weight at birth of American Indians come from numerous studies and demonstrate much variation. An early and very comprehensive report used data from births between July 1964 and June 1969 recorded by the US Public Health Service and obtained from the Health Records Branch of the Division of Indian Health. Mean birth weights were presented by tribe within nine linguistic groups using data from 37,435 infants (the frequencies of LBW (low birth weight, a birth weight less than 2,500 g) or HBW (high birth weight, a birth weight of 4,000 g or more) were not reported) (
Adams and Niswander, 1973). Overall, means were substantially greater than those of non-Native comparison groups. The range of American Indian means across tribes was 3.19 through 3.60 kg for boys and 3.09 to 3.48 kg for girls. Since this comprehensive report was published more than 50 years ago, other studies have reported distributions that are similar to those of White Americans while others support the conclusion that American Indian and Alaskan Native birth weight distribution are shifted higher with higher rates of HBW and fewer or similar rates of LBW () (
Armstrong et al., 1998;
Dyck and Tan, 1995;
Indian Health Service, 1997;
Luo et al., 2004;
Martin et al., 2011;
Munroe et al., 1984;
Thomson, 1990;
Vanlandingham et al., 1988;
Ventura et al., 1998). A striking example is the Canadian Cree. Of more than 2,000 births between 1994 and 2000, the rate of LBW was 2.4% while the rate of HBW was 36.5% (
Willows et al., 2011). Overall, births to American Indians vary over time, by region and by degree of rural isolation.
| TABLE 1Birth size of American Indians |
Size at birth among northern tribes tends to be larger than that of non-Native comparison groups (
Adams and Niswander, 1967;
Caulfield et al., 1998; Moffatt, 1984), and lower birth weights are associated with tribes living in the Southwest: Apache and Navajo, Uto-Aztecans, Zuni, and Tanoan and Keresan (
Adams and Niswander, 1968;
Adams et al., 1970). The exceptions to this generalization are the Pima, Papago and Mohave who are southwestern and had large mean birth weights (
Adams et al., 1970).
More recent reports indicate that the north/south dichotomy may no longer be so clear. Among Saskatchewan American Indian births in the early 1980s, the LBW rate was 6.5 per 1,000 among the American Indian sample, somewhat higher than the rate of 5.2 per 1,000 for the rest of the provincial population (
Edouard et al., 1991). In upstate NY, American Indian births recorded from 1980 to 1986, followed a distribution similar to that of upstate white births despite the presence in the American Indian mothers of several important risk factors for poor prenatal growth (
Buck et al., 1992). Among a selected sample of southwestern area Mescalero Apache children, only 0.3% were LBW.
More recent analyses demonstrate the role of confounding factors on the wide distribution of American Indian births. After adjusting birth weight for such factors, the rate of LBW appears lower among US American Indian and Alaskan Native births occurring between 1985 and 1997 (
Baldwin et al., 2009). Similarly, in a small sample of Canadian Indian births, there was a greater rate of LBW before adjustment for confounders but after adjustment the distribution was more contracted and those rates did not differ (
Wenman et al., 2004).
In 1990, birth weights greater than 4,000 g were present in 12.9% of births to US American Indian mothers compared with 10.9% of births to other mothers in the US (
National Center for Health Statistics, 1993). Among live births reported between 1994 and 1996, only 6.7% were of LBW; HBW births are relatively more frequent: 12.7% of reported live births were of high birth weight as compared to 10.3% of all races in the US (
Indian Health Service, 1997). In 2009, 9.6% of births to American Indians or Alaskan Natives were high birth weight (
Martin et al., 2011) (It is possible that the inclusion of Alaskan Natives affects the comparability of the more recent figures with earlier ones on American Indians alone). American Indian births in the US (1995–2001) displayed a wider distribution than those of non-Hispanic whites with significantly higher rates of LBW (5.8 vs. 4.9%) and preterm delivery (11.0 vs. 8.3%) (
Alexander et al., 2008). Residence may play a role. Ages and educational attainments of US American Indian mothers vary by region (
Alexander et al., 2008). American Indian births in rural, isolated areas of Canada were less likely to be pre-term or LBW compared to urban American Indian births (
Luo et al., 2010). American Indian births in counties with a reservation demonstrated lower rates of VLBW (very low birth weight, a birth weight less than 1500g) compared to American Indian births in counties without a reservation suggesting that reporting bias by locale plays a role in the rates (
Heck et al., 1999), or that risk factors for poor outcomes are more severe in non-reservation counties. Overall, US Native Americans display higher rates of several risk factors for poor birth outcomes including young maternal age (
Martin et al., 2011;
Ventura et al., 1998).
In summary, distributions of American Indian births are quite variable, with many displaying high rates of LBW and, or HBW. Adjustment for risk factors may contract the distributions. The risk factors themselves, low maternal age, smoking, late onset of prenatal care, high maternal BMI, diabetes, and others, are themselves often seen as risk factors for poor outcomes including childhood overweight and obesity (
Adams et al., 2005). This suggests that the life-course towards obesity in American Indian children is begun in the prenatal period. The tendency for American Indian mothers to have large babies may signal the presence of obesogenic influences operating during gestation and signal a trajectory towards later overweight and obesity.