Another Mexican birthweight paradox? The role of residential enclaves and neighborhood poverty in the birthweight of Mexican-origin infants

Examining whether contextual factors influence the birth outcomes of Mexican-origin infants in the US may contribute to assessing rival explanations for the so-called Mexican health paradox. We examined whether birthweight among infants born to Mexican-origin women in the US was associated with Mexican residential enclaves and exposure to neighborhood poverty, and whether these associations were modified by nativity (i.e. mother's place of birth). We calculated metropolitan indices of neighborhood exposure to Mexican-origin population and poverty for the Mexican-origin population, and merged with individual-level, year 2000 natality data (n = 490,332). We distinguished between neighborhood exposure to US-born Mexican-origin population (i.e. ethnic enclaves) and neighborhood exposure to foreign-born (i.e. Mexico-born) Mexican-origin population (i.e. immigrant enclaves). We used 2-level hierarchical linear regression models adjusting for individual, metropolitan, and regional covariates and stratified by nativity. We found that living in metropolitan areas with high residential segregation of US-born Mexican-origin residents (i.e. high prevalence of ethnic enclaves) was associated with lower birthweight for infants of US-born Mexican-origin mothers before and after covariate adjustment. When simultaneously adjusting for exposure to ethnic and immigrant enclaves, the latter became positively associated with birthweight and the negative effect of the former increased, among US-born mothers. We found no contextual birthweight associations for mothers born in Mexico in adjusted models. Our findings highlight a differential effect of context by nativity, and the potential health effects of ethnic enclaves, which are possibly a marker of downward assimilation, among US-born Mexican-origin women.     

Did low birthweight among US blacks really increase?

The low birthweight (LBW) rate among reported United States non-White births increased 32 per cent from 1950 to 1967. States with large increments in non-White LBW rates over the period 1950-67 ("rising LBW states") were compared to states with more stable LBW rates. Paradoxically, states with the most deterioration in LBW rates had the most improvement in LBW risk factors (low income, mothers under age 20 or over age 35, birth order over four). In 1950, at least 9.7 per cent of non-White births in rising LBW states went unreported, and underreporting was biased, with out-of-hospital LBW births who die young least likely to be reported. From 1950 to 1967, non-White out-of-hospital births for the US declined from 42 per cent to 7 per cent, and yearly values for per cent of non-White births in hospital and LBW rates were highly correlated (r = .98). These data suggest that the observed rise in non-White LBW rates from 1950 to 1967 was due in large part to systematic underreporting of LBW births among non-White out-of-hospital deliveries in the 1950s. This underreporting essentially ceased when hospital delivery for non-Whites became nearly universal in the late 1950s and 1960s.     

Why are the low birthweight rates in Brazil higher in richer than in poorer municipalities? Exploring the epidemiological paradox of low birthweight

Socio-economic disadvantage is usually associated with low birthweight (LBW). However, it has been shown that Mexican Americans, despite being economically less advantaged, present LBW rates that are similar to or lower than those found among white women in the US. This fact has been called 'the epidemiological paradox of low birthweight'. Natality data from Brazil revealed the existence of a similar paradox: LBW rates are higher in more developed than in less developed regions within the country. In this study, data from two population-based cohort studies carried out in the nineties, including 2439 births in Sao Luis, a poor city in north-eastern Brazil, and 2839 births in Ribeirao Preto, a socio-economically well-off city in south-eastern Brazil, were used to explore this paradox. The method proposed by Wilcox and Russell and a graphic analysis of the frequency distribution of birthweight according to gestational age were used to provide indirect information about possible gestational age misclassification. Contrary to expectations, the LBW rate was higher in Ribeirao Preto than in Sao Luis (10.7 vs. 7.6%, P <0.001), while preterm birth (PTB) rate (12.7 vs. 12.1%, P=0.520) and percentage of small-for-gestational-age (SGA) infants (12.5 vs. 13.5%, P=0.290) were similar for the two cities. However, SGA rate among preterm infants was higher in Ribeirao Preto (16.4 vs. 9.8%, P=0.014). A bimodal distribution of birthweight was observed for children with less than 32 weeks in Sao Luis. As estimated by the Wilcox and Russell method, the residual distribution was greater in Ribeirao Preto than in Sao Luis (3.4 vs. 2.4%). Part of the LBW paradox observed for the two cities was due to the higher PTB rate and higher number of preterm SGA infants in Ribeirao Preto. Factors such as greater medical intervention in preterm newborns close to the end of pregnancy in more developed municipalities, artefacts in the determination of gestational age, and the under-registration of livebirths and registration of livebirths as stillbirths in less developed municipalities may explain why LBW rates in Brazil are higher in richer than in poorer municipalities.     

Is low birthweight associated with dental caries in permanent dentition?

The aim of this study was to test the hypothesis of association between low birthweight and dental caries. This study used data from the Third National Health and Nutritional Examination Survey, 1988-94 (NHANES III) including 7- to 11-year-old children with complete dental caries information (n = 2439). Two case definitions for dental caries were used: presence of the disease in more than one tooth, and more than 10% of teeth with dental caries. Low birthweight was defined as those children born weighing <2500 g. Other covariates used in the analysis were sex, age, poverty level, race/ethnicity, frequency of dental visit, education of head of household, daily sucrose intake, blood lead level and blood cotinine level. A separate analysis was conducted for each case definition of dental caries. Bivariable and stratified analysis was performed followed by multivariable Poisson regression. The Stata 8.0 statistical package was used to take into consideration the multistage complex sample. For the definition of more than one tooth with dental caries, the prevalence ratios (PRs) for bivariable and multivariable analyses were 1.28 [95% confidence interval (CI): 0.48, 3.42] and 1.01 [95% CI: 0.41, 2.49] respectively. For the definition of >10% of teeth with dental caries, the PRs for bivariable and multivariable analyses were 1.33 [95% CI: 0.60, 2.96] and 1.32 [95% CI: 0.75, 2.30] respectively. This study could not demonstrate an association between low birthweight and dental caries in permanent teeth of 7- to 11-year-old American children.     

A nested case–control study of low birthweight among cosmetologists

Objective  

This study was designed to determine whether licensed female cosmetologists with a low birthweight child were more likely to perform specific occupational tasks during pregnancy than cosmetologists who had a normal weight child. We also investigated certain salon characteristics in relation to low birthweight status.     

Is conception delay a risk factor for reduced gestation or birthweight?

Previous studies have suggested an association between delays in conception and adverse perinatal outcomes, specifically, low birthweight and preterm birth. We investigated the relationship between conception delay (defined as >6 months to become pregnant) and three perinatal outcomes: low birthweight (LBW; <2500 g), preterm birth (PTB; <37 weeks), and small-for-gestational-age (SGA; <10th percentile weight for given gestational age) using data from the Collaborative Perinatal Project. The study cohort was limited to pregnancies with a known time-to-pregnancy (n = 8465; 15%). Generalised estimating equations were used to estimate odds ratios (OR) and 95% confidence intervals [CI] for risk of adverse perinatal outcomes accounting for the clustering of pregnancy outcomes for women with more than one pregnancy. After adjusting for confounders, all ORs were close to the null (LBW, OR = 1.01; 95% CI = 0.86, 1.20), (PTB, OR = 1.10; 95% CI = 0.95, 1.27), (SGA, OR = 1.06; 95% CI = 0.91, 1.25). Thus, we found no evidence to support an adverse relationship between conception delay and decrements in gestation or birthweight among this select sample of fertile women, even after varying the cut-point for defining conception delay.     

Can accurate data on birthweight be obtained from health interview surveys?

BACKGROUND: Because hospital records rarely exist for a representative sample of the population in developing countries, researchers frequently rely on birthweight data from surveys. Yet, the quality of these data has rarely been evaluated. This study explores the accuracy of birthweight information in six demographic and health surveys in Latin America conducted in the early 1990s: two in Guatemala, and one each in Bolivia, Costa Rica, El Salvador and Peru. METHODS: The quality of the birthweight reports is assessed by examining the plausibility of estimates of the proportion of newborns reported to have been weighed and estimates derived from the numerical weights, by characteristics of the delivery and maternal education. RESULTS: The estimates suggest that a substantial proportion of women whose newborns were probably never weighed report a birthweight. For all of the surveys, with the possible exception of Costa Rica, the average birthweights appear to be too high, and the estimates of the prevalence of low birthweight too low. In addition, the data reveal anomalous patterns, such as higher birthweights for home as compared with hospital deliveries. CONCLUSIONS: These findings suggest that estimates of low birthweight derived from surveys in developing countries are likely to portray an overly optimistic picture of children's and women's health status. More information about the underlying source of these data are needed not only to provide additional insight into the degree of error characterizing existing estimates, but also to improve data collection strategies in future health interview surveys.     

Are very low birthweight births among American Indians and Alaska Natives underregistered?

BACKGROUND: International infant mortality rates vary widely. This variation has been attributed to many factors, including differential reporting. In the US, American Indians and Alaska Natives (AI/AN), who generally have low socioeconomic status, have a low neonatal mortality rate. One possible explanation is underregistration of very low birthweight (VLBW, < 1,500 g) births. We hypothesized that underregistration may occur disproportionately among AI/AN residing on or near reservations (areas controlled by an American Indian group). We estimated infant mortality in these areas. METHODS: Linked birth-infant death files for 1989-1991 were used to compare VLBW and neonatal mortality among AI/AN infants in counties with reservations with those in non-reservation counties. The VLBW rates for non-reservation counties were applied to the reservation risk distribution to calculate directly adjusted VLBW and neonatal mortality rates for reservation counties. This method assumes that greater registration in non-reservation counties yields a more accurate estimate of the relationship between risk factors and outcomes. RESULTS: Despite a higher prevalence in reservation counties of risk factors, the reported VLBW rate was 0.84% in reservation and 1.17% in non-reservation counties. The neonatal mortality rate was 5.4 per 1,000 in reservation counties and 6.0 in non-reservation counties. Direct adjustment yielded a VLBW rate of 1.28% (95% CI: 1.14-1.39) and a neonatal mortality rate of 6.7-9.8 per 1,000 in reservation counties. CONCLUSIONS: Reported neonatal mortality among AI/AN may understate the true rate due to underregistration of VLBW births. Direct adjustment may be useful in estimating infant mortality rates for populations with incomplete vital registration.     

Does a medical home influence the effect of low birthweight on health outcomes?

The objective of this study was to investigate the possible modifying effect of medical home on the association between low birthweight and children's health outcomes. The analytic sample included children 5 years and under from the 2007 National Survey of Children's Health whose mothers were the primary respondents and who had non-missing covariate information (n = 19,356). Controlling for sociodemographic factors, logistic and ordinal regression models estimated the presence of developmental, mental/behavioral or physical health outcomes, condition severity, and health status by birthweight, medical home, and their interaction. Prevalence estimates of physical, developmental, mental/behavioral and severe conditions among those with any conditions as well as fair/poor overall health were 8.9, 6.8, 2.4, 41.6, and 2.5 %, respectively. Overall, low compared to normal birthweight children had a higher prevalence of physical and developmental conditions and fair/poor health (15.2 vs. 8.3 %, 11.1 vs. 6.4 %, 4.5 vs. 2.3 %, respectively). Medical home did not significantly modify the effect of birthweight on health outcomes; however, prevalence of all outcomes was higher for children without a medical home. Adjusted models indicated that low birthweight children were almost twice as likely as normal birthweight children to have a physical or developmental condition and poorer overall health, regardless of having a medical home. Having a medical home was associated with equally improved health outcomes among normal and low birthweight children. Adequacy and frequency of medical home care should be investigated further, especially among low birthweight children.     

Does government provision of healthcare explain the relationship between income inequality and low birthweight?

This paper estimates the relationship between state and county income inequality and low birthweight (LBW) in the U.S. It examines whether more unequal societies are also less healthy because such societies have lower investment in population health. The model includes an extensive list of community and individual controls and community fixed-effects. Results show that unequal states in fact have greater social investments, and absent these investments children born in such states would be more likely to be LBW. Using alternate measures of inequality reveals that income inequality in the upper tail of the income distribution is not related to LBW; but inequality in the lower tail of the income distribution is associated with increased LBW where the supply of healthcare mitigates the effect of income inequality. Consistent with prior findings, county income inequality is not significantly related to LBW.     

Is birthweight an appropriate health‐outcome measure for Torres Strait Islander babies?

BACKGROUND: Although Torres Strait Islanders (TSIs) are often combined with Aborigines, they are a distinct group and would prefer to be considered separately. The Queensland Perinatal Data Collection (QPDC) has been the only population-based, perinatal collection in Australia that has distinguished between Aboriginal and TSI mothers. It provided a unique opportunity to compare outcome measures based on birthweight in the TSI, Aboriginal and white populations. TSIs were of particular interest because recent research from overseas suggests that in groups with high rates of obesity and diabetes, birthweight is not a valid outcome measure. This is of concern because outcome measures based on birthweight have been proposed as a way of monitoring the neonatal health of Indigenous Australians. METHODS: Retrospective analysis of 10 years of routine data from the QPDC. RESULTS: TSIs had a birthweight distribution similar to that of whites, but mortality rates similar to those of Aborigines. For birthweights between 2500 g and 4000 g, TSIs had mortality rates that were 2.5 times higher than those for whites (95% CI: 1.3 to 4.2). CONCLUSIONS: Although birthweight is widely used, it is not necessarily a valid outcome measure in all populations. For TSIs, maternal conditions such as obesity and diabetes might cause changes in the uterine environment that produce heavier, but not healthier babies.     

Is birthweight a good marker for gestational exposures that increase the risk of adult disease?

There is much evidence of a link between low birthweight and elevated risk of adult cardiovascular disease, from humans and experimental animals. However, if one relies on data linking birthweight to coronary heart disease to estimate the public health implications of this association, the effects are likely to be modest. The focus on birthweight may be misplaced, because reduced size at birth may not be in the causal pathway linking gestational factors to disease in adult offspring. We need to know more about this before we can estimate the public health implications of gestational factors and assess the potential for intervention. The most studied gestational factor is maternal nutrition. We review here evidence for and against birthweight being in the causal pathways between suboptimal maternal nutrition and increased risk of adult disease in the offspring and provide evidence suggesting that birthweight is not in all of them. From a public health point of view, we suggest that future research in this field should focus on modifiable gestational exposures that may be linked to adult disease, whether or not they influence size at birth.     

What is driving the black–white difference in low birthweight in the US?

This is a first effort to quantify the contribution of different factors in explaining racial difference in low birthweight rate (LBW). Mother's health, child characteristics, prenatal care, socioeconomic status (SES), and the socioeconomic and healthcare environment of mother's community are important inputs into the birthweight production function, and a vast literature has delved into obtaining causal estimates of their effect on infant health. What is unknown is how much of the racial gap in LBW is explained by all these inputs together. We apply a nonlinear extension of the Oaxaca-Blinder method proposed by Fairlie to decompose this gap into the portion explained by differences in observed characteristics and the portion that remains unexplained. Data are obtained from several sources in order to capture as many observables as possible, although the primary data source is the Natality Detail Files. Results show that of the 6.8 percentage point racial gap in LBW, only 0.9-1.9 points are explained by white-black differences in endowments across those measures, and of those endowments, most of the gap in LBW is explained by the differences in SES. The unexplained difference is attributed to racial differences in the returns to or the marginal product of investments in infant health.     

Within prisons,is there an association between the quantity of prenatal care and infant birthweight?

There is still controversy surrounding the effectiveness of prenatal care in reducing low birthweight. In addition, very few studies have assessed the relationship between prenatal care and infant birthweight among pregnant women within the prison system. We sought to ascertain whether there is an association between the quantity of prenatal care and infant birthweight among pregnant women within such a setting. We examined the prison medical records of 147 infants born to women delivering at term (37-41 weeks of gestation) between 1 January 2002 and 31 December 2004 who were incarcerated during pregnancy in Texas state prisons. Linear regression was used to evaluate the association between the number of prison prenatal care visits and infant birthweight while adjusting for potential confounders (age, gravidity, maternal education, maternal race, history of substance use, history of alcohol use, history of tobacco use and the presence of any chronic disease). We also adjusted for the interaction between the gestational age at admission to prison and the number of prison prenatal care visits. There was a statistically significant 120.5 g increase in adjusted mean birthweight with each additional prison prenatal care visit (P = 0.001) among study infants whose mothers entered prison during the first trimester. This trend was not observed among women who came in after the first trimester. There appears to be a positive association between the amount of prison prenatal care and infant birthweight among incarcerated pregnant women delivering at term, but this association appears to be limited to women entering prison during the first trimester of pregnancy.     

Does reducing infant mortality depend on preventing low birthweight? An analysis of temporal trends in the Americas

Low birthweight (LBW) is highly associated with death during infancy, and countries with the highest LBW rates also have the highest infant mortality rates. We compared temporal trends in LBW with both overall and birthweight-specific infant mortality in United States, Canada, Argentina, Chile, and Uruguay over two time periods, using cohort and cross-sectional analysis of national population-based vital statistics for 1985-89 and 1995-98. Infant mortality diminished substantially (RR = 0.60-0.80 for the later vs. earlier periods) and to a similar degree in all birthweight categories in all five study countries, despite an increase in LBW in the US and Uruguay, minimal changes in Canada and Argentina, and a decrease in Chile. The strength of the (positive) association between LBW and overall infant mortality diminished over the two time periods (from r(s) = +0.80 to +0.25 and RR per SD increase in LBW rate from 2.13 [2.09, 2.17] to 1.76 [1.74, 1.79]). The proportion of infant deaths occurring among LBW infants was negatively correlated with overall infant mortality in both time periods (r(s) = -0.30 and -0.60, RR = 0.68 [0.67, 0.68] and 0.47 [0.46, 0.47]). Developed and less developed countries in the Americas have succeeded in reducing infant mortality in all birthweight groups despite inconsistent changes in LBW rates, and none has achieved this success primarily by reducing LBW. Although our results are not necessarily generalisable to the least developed countries in South Asia and sub-Saharan Africa, it is likely that all countries can substantially reduce their infant mortality rates by improving the care of infants at normal and low birthweights.     

The increase in very‐low‐birthweight infants in Germany: artefact or reality?

Earlier findings have shown that after unification with the Federal Republic of Germany (FRG) in October 1990 the proportion of very-low-birthweight infants in the former German Democratic Republic (GDR) increased. This study seeks to explore this observation in more detail at the regional level. The analysis of aggregate data of live births in Germany between 1991 and 1997 shows an increasing proportion of very-low-birthweight infants as well as a general trend towards heavier babies in both east and west. The growing proportion of live born infants at very low birthweights in the east, however, seems to be due, in part, to increased registration, most likely reflecting the introduction of the more comprehensive (western) definition of a live birth with unification in October 1990. A fairly distinct east-west pattern in the birthweight distribution present in 1991 had almost disappeared by 1997 and given way to a north-south one.