The contribution of attenuated selection in utero to small-for-gestational-age (SGA) among term African American male infants

Male twinning after the 2008 Obama election: A test of symbolic empowerment

On November 4, 2008, Barack Obama was elected the first Black President of the United States. His campaign and electoral win served as a symbol of hope for a more just future, fostering an "Obama effect" that appears associated with improved well-being among non-Hispanic (NH) Black communities. Situating the Obama election within the symbolic empowerment framework, we consider the potentially protective role of the Obama election on NH Black fetal death, an important but understudied measure of perinatal health that has stark racial disparities. Using restricted-use natality files from the National Center for Health Statistics, we proxy fetal death using the male twin rate (number of twins per 1000 male live births). Male twins have a relatively high risk of in utero selection that is sensitive to maternal and environmental stressors, making the twin rate an important marker of fetal death. We then estimate interrupted time-series models to assess the relation between the Obama election and male twin rates among NH Black births across monthly conception cohorts (February 2003-October 2008). Greater-than-expected male twin rates signal less susceptibility to fetal loss. Results indicate a 4.5% higher male twin rate among all NH Black cohorts exposed in utero to the Obama election, after accounting for historical and NH white trends (p < 0.005). The greater-than-expected rates concentrated among births conceived in the months preceding Obama's nomination at the Democratic National Convention and Obama's presidential win. These results suggest a salutary perinatal response to election events that likely reduced NH Black fetal loss. They also indicate the possibility that sociopolitical shifts can mitigate persisting NH Black-NH white disparities in perinatal health.

A novel indicator of selection in utero

Background and objectives

Selection in utero predicts that population stressors raise the standard for how quickly fetuses must grow to avoid spontaneous abortion. Tests of this prediction must use indirect indicators of fetal loss in birth cohorts because vital statistics systems typically register fetal deaths at the 20th week of gestation or later, well after most have occurred. We argue that tests of selection in utero would make greater progress if researchers adopted an indicator of selection against slow-growing fetuses that followed from theory, allowed sex-specific tests and used readily available data. We propose such an indicator and assess its validity as a dependent variable by comparing its values among monthly birth cohorts before, and during, the first 10 months of the COVID-19 pandemic in Sweden.

Methodology

We apply Box-Jenkins methods to 50 pre-pandemic birth cohorts (i.e., December 2016 through January 2020) and use the resulting transfer functions to predict counterfactual values in our suggested indicator for selection for ten subsequent birth cohorts beginning in February 2020. We then plot all 60 residual values as well as their 95% detection interval. If birth cohorts in gestation at the onset of the pandemic lost more slow-growing fetuses than expected from history, more than one of the last 10 (i.e. pandemic-exposed) residuals would fall below the detection interval.

Results

Four of the last 10 residuals of our indicator for males and for females fell below the 95% detection interval.

Conclusions and implications

Consistent with selection in utero, Swedish birth cohorts in gestation at the outset of the COVID-19 pandemic included fewer than expected infants who grew slowly in utero.

Male-to-Female Ratios, Race/Ethnicity, and Spontaneous Preterm Birth among 11 Million California Infants

OBJECTIVE

An observed disparity in population-scale data are a larger number of males among preterm births (PTBs). We investigated spontaneous PTB risk among women of various race/ethnic groups in combination with infants' sex.

STUDY DESIGN

This observational study was conducted in > 10 million California births (1991-2012) using birth certificates linked with maternal and infant hospital discharge data.

RESULTS

Male-to-female ratios among term (37-42 weeks) infants exhibited the narrow ratio range 1.02 to 1.06 across race/ethnic groups. Such ratios among spontaneous PTBs were generally larger for all race/ethnic groups except non-Hispanic blacks. For blacks, ratios tended to be lower and similar to their term birth counterpart, 1.03. Hazard ratios adjusted for maternal age and education for non-Hispanic blacks were 0.99 (95% confidence interval [CI] 0.90-1.09), 1.01 (95% CI 0.95-1.08), 0.98 (95% CI 0.94-1.03), and 1.03 (95% CI 1.01-1.05), respectively, for gestational week groupings of 20 to 23, 24 to 27, 28 to 321, and 32 to 36. Hazard ratios for non-Hispanic whites for the same groupings were 1.08 (95% CI 0.98-1.18), 1.13 (95% CI 1.07-1.19), 1.21 (95% CI 1.17-1.25), and 1.18 (95% CI 1.17-1.19).

CONCLUSION

Why male-to-female ratios are similar across gestational ages in blacks but substantially higher in other race/ethnic groups is theoretically considered relative to inflammation, stress, and other influences.

Factors associated with small- and large-for-gestational-age in socioeconomically vulnerable individuals in the 100 Million Brazilian Cohort

BACKGROUND

Evidence points to diverse risk factors associated with small- (SGA) and large-for-gestational-age (LGA) births. A more comprehensive understanding of these factors is imperative, especially in vulnerable populations.

OBJECTIVES

To estimate the occurrence of and sociodemographic factors associated with SGA and LGA births in poor and extremely poor populations of Brazil.

METHODS

The study population consisted of women of reproductive age (14-49 y), whose last child was born between 2012 and 2015. INTERGROWTH 21st consortium criteria were used to classify weight for gestational age according to sex. Multinomial logistic regression modeling was performed to investigate associations of interest.

RESULTS

Of 5,521,517 live births analyzed, SGA and LGA corresponded to 7.8% and 17.1%, respectively. Multivariate analysis revealed greater odds of SGA in children born to women who self-reported as black (OR: 1.21; 95% CI: 1.19, 1.22), mixed-race (parda) (OR: 1.08; 95% CI: 1.07, 1.09), or indigenous (OR: 1.11; 95% CI: 1.06, 1.15), were unmarried (OR: 1.08; 95% CI: 1.07, 1.08), illiterate (OR: 1.47; 95% CI: 1.42, 1.52), did not receive prenatal care (OR: 1.57; 95% CI: 1.53, 1.60), or were aged 14-20 y (OR: 1.21; 95% CI: 1.20, 1.22) or 35-49 y (OR: 1.12; 95% CI: 1.10, 1.13). Considering LGA children, higher odds were found in infants born to women living in households with ≥3 inadequate housing conditions (OR: 1.11; 95% CI: 1.10, 1.12), in indigenous women (OR: 1.22; 95% CI: 1.19, 1.25), those who had 1-3 y of schooling (OR: 1.18; 95% CI: 1.17, 1.19), 1-3 prenatal visits (OR: 1.16; CI 95%: 1.14, 1.17), or were older (OR: 1.26; 95% CI: 1.25, 1.27).

CONCLUSIONS

In poorer Brazilian populations, socioeconomic, racial, and maternal characteristics are consistently associated with the occurrence of SGA births, but remain less clearly linked to the occurrence of LGA births.

African American Unemployment and the Disparity in Periviable Births

Periviable infants (i.e., born before 26 complete weeks of gestation) represent fewer than .5% of births in the US but account for 40% of infant mortality and 20% of billed hospital obstetric costs. African American women contribute about 14% of live births in the US, but these include nearly a third of the country’s periviable births. Consistent with theory and with periviable births among other race/ethnicity groups, males predominate among African American periviable births in stressed populations. We test the hypothesis that the disparity in periviable male births among African American and non-Hispanic white populations responds to the African American unemployment rate because that indicator not only traces, but also contributes to, the prevalence of stress in the population. We use time-series methods that control for autocorrelation including secular trends, seasonality, and the tendency to remain elevated or depressed after high or low values. The racial disparity in male periviable birth increases by 4.45% for each percentage point increase in the unemployment rate of African Americans above its expected value. We infer that unemployment—a population stressor over which our institutions exercise considerable control—affects the disparity between African American and non-Hispanic white periviable births in the US.

A test of oscillation in the human secondary sex ratio

Background and objectives

The sex ratio of human birth cohorts predicts the health and longevity of their members. Most literature invokes natural selection in support of the argument that heritable tendencies to produce male or female offspring induce oscillation in the sex ratio and its sequelae. Tests of the argument remain exceedingly rare because they require vital statistics describing many generations of a population both unaffected by migration and exposed to an exogenous stressor virulent enough to change the sex ratio at birth. We contribute to the literature by using time-series modeling to detect oscillation in the best data currently available for such a test.

Methodology

We apply rigorous time-series methods to data describing Sweden from 1751 through 1830, a period when the population not only aged in place without migration, but also exhibited the effects of an Icelandic volcanic eruption including a historically low secondary sex ratio. That very low sex ratio should have induced oscillation if heritable mechanisms appear in humans.

Results

We detected oscillation in the ratio but not that predicted by heritable tendencies to produce males or females. We found peak-to-trough oscillation at 14 rather than the approximately 32 years expected from the heritable tendencies argument.

Conclusions and implications

Our findings suggest that mechanisms other than perturbation of heritable tendencies to produce males or females induce oscillation in the human secondary sex ratio. These other mechanisms may include reproductive suppression and selection in utero.

LAY SUMMARY

The male to female ratio in human birth cohorts predicts longevity but its variation over time remains unexplained. We test the long-held theory that the ratio oscillates due to heritable tendencies to produce males or females. We find oscillation, but it appears due to social processes rather than heritable mechanisms.

Comparação entre duas curvas de crescimento para detectar recém-nascidos pequenos para a idade gestacional

Resumo Objetivos: comparar duas curvas de crescimento, Lubchenco e Fenton e Kim, na detecção de recém-nascidos (RN) pequenos para idade gestacional (PIG) segundo sexo. Métodos: estudo transversal de dados de RN, de 01/01/2010 a 31/12/2012 Definiu-se PIG o peso ao nascer (PN) inferior ao percentil 10 para idade gestacional (IG) segundo as curvas Lubchenco e Fenton & Kim. Mensurou-se a concordância entre as curvas pelo Método de Kappa para o diagnóstico de PIG segundo sexo e IG. Construíram-se curvas dos percentis 10 de PN e referenciais, por sexo, utilizando função polinomial de terceiro grau. Para comparar e medir associações entre as variáveis sexo, IG e PIG foram utilizados o teste do qui-quadrado de Pearson e regressão logística bivariada, respectivamente. Significância: p<0,05. Resultados: foram incluídos 2364 recém-nascidos no estudo. As curvas Fenton e Kim detectaram mais RN PIG, cuja taxa foi 16,2%, enquanto as Lubchenco detectaram 3,3% (p<0,001; k=0,292). A discordância foi maior com o aumento da IG. O sexo masculino se associou à maior chance de nascer PIG 1,6 vezes em relação ao feminino (OR= 1,59; IC95%= 1,28-2,00; p<0,001). Conclusões: as curvas Fenton e Kim detectaram mais RN PIG. O nascimento PIG foi mais frequente no sexo masculino. Os achados contribuem para adoção de estratégias visando melhorias no diagnóstico, cuidados e prognóstico.