Socio‐economic disparities in preterm birth: causal pathways and mechanisms

Abstract

SummaryPreterm birth is the leading cause of infant mortality in industrialised societies. Its incidence is greatly increased among the socially disadvantaged, but the reasons for this excess are unclear and have been relatively unexplored. We hypothesise two distinct sets of causal pathways and mechanisms that may explain social disparities in preterm birth. The first set involves chronic and acute psychosocial stressors, psychological distress caused by those stressors, increased secretion of placental corticotropin releasing hormone (CRH), changes in sexual behaviours or enhanced susceptibility to bacterial vaginosis and chorioamnionitis, cigarette smoking or cocaine use, and decidual vasculopathy. The second hypothesised pathway is a gene±environment interaction based on a highly prevalent mutation in the gene for methylenetetrahydrofolate reductase (MTHFR), combined with low folate intake from the diet and from prenatal vitamin supplements, consequent hyperhomocysteinemia, and decidual vasculopathy.We propose to test these hypothesised pathways and mechanisms in a nested casecontrol study within a prospectively recruited and followed cohort of pregnant women with singleton pregnancies who deliver at one of four Montreal hospitals that serve an ethnically and socio-economically diverse population. Following recruitment during the late first or early second trimester, participating women are seen at 24±26 weeks, when a research nurse obtains a detailed medical and obstetric history; administers several scales to assess chronic and acute stressors and psychological function; obtains blood samples for CRH, red blood cell and plasma folate, homocysteine, and DNA for the MTHFR mutation; and performs a digital and speculum examination to measure cervical length and vaginal pH and to obtain swabs for bacterial vaginosis and fetal fibronectin. After delivery, each case (delivery at 5 37 completed weeks following spontaneous onset of labour or prelabour rupture of membranes) and two controls are selected for placental pathological examination, hair analysis of cotinine, cocaine, and benzoylecgonine, and analysis of stored blood and vaginal specimens. Statistical analysis will be based on multiple logistic regression and structural equation modelling, with sequential construction of models of potential aetiological determinants and covariates to test the hypothesised causal pathways and mechanisms.The research we propose should improve understanding of the factors and processes that mediate social disparities in preterm birth. This improved understanding should help not only in developing strategies to reduce the disparities but also in suggesting preventive interventions applicable across the entire socioeconomic spectrum.

Maternal and neonatal characteristics of extremely low birth weight infants who die in the first day of life

“…In addition, black mothers have been shown to be at increased risk of recurrent preterm delivery and to receive different prenatal care. 13,14 These differences include decreased use of tocolysis, as compared to white mothers, consistent with the observed decrease in tocolysis in the present cohort from the second epoch. 15 In addition, the perinatal mortality rate in black infants is dramatically higher than in white infants even when controlling for early access to prenatal care, demographic characteristics, and pregnancy complications.…”

How many low birthweight babies in low- and middle-income countries are preterm?

“…25,29,51,65 Thus, countries with high prevalence of risk factors (such as low maternal body mass index and malaria) with a resulting high prevalence of term LBW are also more likely to present high rates of preterm LBW births. In addition, a number of studies 7,23,28,45,50 show that preterm births are more frequent among poor populations. For these reasons, the current fi ndings are more biologically and epidemiologically plausible than those from earlier studies based on data collected pre-1990, which showed little variation of preterm rates across a wide range of LBW prevalences.…”

Immigrants and Preterm Births: A Nationwide Epidemiological Study in Sweden

“…Maternal education is one aspect of socioeconomic status that most consistently predicts poor birth outcomes [1]. Other maternal demographic, social and health-related factors have been associated with these adverse birth outcomes, such as single marital status [2], smoking [3][4][5][6][7][8][9][10][11], diabetes [12][13][14] and low social capital [15]. For example, we recently showed that women from Turkey, Iran, Asia, and Latin…”