Associations between neighborhood violence during pregnancy and birth outcomes: evidence from São Paulo’s Western Region Birth Cohort

Low birth weight accounts for more than 80% of all neonatal mortality globally [1]. In 2015, more than 1 million children under 5 died because of preterm birth complications globally [2]. Neonates born with low birth weight – about two-thirds of which are preterm [1] - face higher morbidity risks, increased risk of stunting, increased risk of long-term development impairment, as well as increased vulnerability to chronic disease [1‐7].

Violence is a growing public health concern with immediate and long-term influences on population health [8‐10]. Contrary to some positive trends observed in high-income countries (HIC) in recent years [10], homicide rates have been increasing in Latin America over the past years [11]. An estimated homicide rate of 28.5 implies that Latin America’s crime rates are approximately 8 times higher than those seen in HICs on average and 14 times those seen in low-middle-income countries (LMICs) in the Western Pacific Region [11].

Exposure to violence has been consistently associated with mental health problems and high-risk behaviors such as alcohol, smoking, and drug abuse, which threaten the wellbeing of both adult and child populations [9, 12], and which are also well-known risk factors for low birth weight, small-for-gestational-age, and preterm birth. Fear of crime can trigger anxiety and feelings of isolation, victimization, powerlessness, and normlessness [13], particularly among women [14]. Moreover, stress may indirectly increase the risk of adverse birth outcomes through the development of depressive symptoms and low commitment to prenatal care [15‐18], and inadequate dietary intake [19].

Chronic exposure to such environmental stress can trigger neural or neuroendocrine responses, change the functioning of the hypothalamic-pituitary-adrenal (HPA) axis and lead to increased allostatic load [20]. Stress may also increase the placental secretion of corticotrophin-releasing hormones, which increase prostanoids and stimulate uterine contractions and can induce preterm delivery [17, 20‐23]. Studies have also shown that increased activation of the maternal HPA axis and sympathetic nervous systems can induce restrictions in uterine vasculature, resulting in intrauterine growth restriction or preterm birth [7].

A growing body of literature has tried to link external violence’s to adverse birth outcomes at the area level [24‐33]. The large majority of studies are based on neighborhood comparisons in the United States and likely allow only limited insight into the impact of violence in low-income settings due to the large structural differences in neighborhoods and public support systems. The few studies that have been conducted in low-income and high crime exposure areas have mostly focused on sociopolitical violence and generally found sizeable increases in adverse birth outcomes in response to major violence outbreaks [24, 34, 35]. This is consistent with other studies focusing on more extreme forms of violence, such as terrorist attacks and civil/war conflicts, generally finding large increases in the risk of pregnancy complications outcomes after such major events [24, 36, 37]. Moreover, the effects of violence on adverse birth outcomes might differ from areas where violence is rare and areas where violence is considered endemic, having each additional violent crime smaller adverse consequences on birth outcomes due to the process of adaptation [27].

In this paper, we aim to explore the relationship between exposure to violent crime in close vicinity and three of the most common adverse birth outcomes: preterm birth, small-for-gestational-age, and low birth weight in one of the largest metropolitan areas of the world [38]. Using a novel data set, we aim to improve the understanding of the health consequences of violent crimes on pregnant women and their offspring in a low-income population. Our initial hypothesis is that the occurrence of violent crime close to home is associated with these adverse birth outcomes, independent of maternal and socioenvironmental characteristics.

Among the 6207 children in the ROC-Cohort, 44 were stillbirths and excluded from the analysis. The likelihood of being stillborn was not associated with violence exposure during pregnancy in our sample (0.99; 95%CI: 0.92–1.06). Additionally, 895 mother-child dyads were excluded due to an address outside of the studied setting. Overall, 5268 children and their mothers met the inclusion criteria for this study.

Mothers who did not respond to the postpartum questionnaire (n = 2008) did not differ from those who completed (n = 3260) the survey with respect to the type of birth, gestational length category, birth weight and length, and child sex.

398 (7.8%) births were classified as SGA, 369 (7.0%) as PT, and 355 (6.7%) as LBW. Table 1 shows the frequency of each type of crime during pregnancy by exposure quintile. From 2011 to 2014, there were 8504 violent crimes in the São Paulo municipality – only 13 of these could not be geolocated (0.15%). 339 (4%) of all crimes in the municipality were located in the Butanta-Jaguaré area (where all children of the cohort reside). During the first two trimesters, the mean number of crimes occurring within a 1-km radius from home was 4.2 (SD ± 4.8). The large majority of violent crimes were murders; death resulting from police intervention was the second most common type of violent crime. Women with the lowest exposure quintile were on average exposed to 0.45 (SD ± 0.5) violent crimes, while women in the fifth quintile were exposed on average to 12.7 (SD ± 4.5) violent crimes. Only 19% of women were not exposed to any violent event in a 1 km radius during pregnancy; some women in the top exposure quintile experienced more than 30 violent crimes during the first two trimesters.

Figure 1 shows the geographic distribution of the outcomes and violent crimes in the studied area. Areas colored in red represent the highest crime exposure; blue areas are safest. Panel A of Figure one shows the overall spatial distribution of children in the study area. Panels B, C, and D illustrate the spatial distribution of the three adverse birth outcomes.

The prevalence of SGA, PT and LBW were 6.7, 7.9, and 9.5% (SGA), 6.5, 6.4, and 6.3% (PT), and 5.4, 7 and 7.5% (LBW) in the first, third, and fifth exposure quintiles, respectively. Table 2 shows the distribution of SGA, PT, and LBW birth outcomes and family characteristics by exposure quintile using the raw (non-imputed) data. The number of available data points for each variable as well as additional information on the MICE can be found in Supplementary file 2. Table 2 also shows the bivariate analysis between continuous violent crimes quintiles (range 1 to 5), and birth outcomes, and child and family characteristics. In bivariate analysis LBW was strongly associated with crime exposure (1.09; 95%CI: 1.02–1.17, p = 0.014), while PT and SGA displayed positive but not statistically significant associations with violent crimes. Upper middle (0.91; 95%CI: 0.85–0.98, p = 0.013) and high (0.83; 95%CI: 0.77–0.89, p <  0.001) SES status was negatively associated with violent crimes. Physical violence during pregnancy reported in the postpartum questionnaire was also negatively associated with violent crimes (0.79; 95%CI: 0.66–0.95, p = 0.013).

Figure 2 shows the bivariate relationship between exposure to violent crime and the proportion of infants born SGA (panel a), preterm (panel b) and LBW (panel c). Table 3 shows the unadjusted and adjusted associations between violent crime exposure during pregnancy and adverse birth outcomes. All models were adjusted using maternal age, child sex, education, and socioeconomic status. Relative to children from the lowest violence quintile, living in the highest violence quintile was associated with a 46% increase in SGA odds in the unadjusted model (1.46; 95%CI: 1.10–1.93). After adjustment for covariates, risk factors, and SES status, the estimated odds ratio (OR) slightly decreased (1.41; 95%CI: 1.06–1.89). In the adjusted model, PT birth odds increased nonlinearly (Fig. 2) with violence exposure, varying the estimated ORs from 1.16 (95%CI: 0.84–1.59) on quintile 2, 1.35 (95%CI: 1.01–1.80) on quintile 4, and 1.01 (95%CI: 0.72–1.40) on quintile 5. The estimated risk of LBW increased almost linearly with exposure quintiles, with an estimated OR of 1.43 (95%CI: 1.03–1.98) for the top quintile. In terms of the included covariates, smoking during pregnancy was the most consistent risk factor for all birth outcomes analyzed in this study, with estimated ORs of 1.83 for SGA (95%CI: 1.32–2.55), 2.04 for PT birth (95%CI: 1.47–2.82), and 2.89 for LBW (95%CI: 2.07–4.03). Physical violence reported by the mother during pregnancy (in the post-partum interview) was associated with more than twice the odds of LBW (2.12; 95%CI: 1.03–4.36). SES and maternal education were not associated with the outcomes in our analysis.

This study uses a novel data set from Brazil to explore the empirical associations between neighborhood-level exposure to violent crime and birth outcomes. Our study yields three main findings: first, exposure to violent crimes is very high among pregnant women in the urban areas studied. Based on the São Paulo estimated population by the Brazilian Institute of Geography and Statistics and violent crimes reports extracted by us from the Secretariat of Public Safety of the State of São Paulo, from 2011 to 2014, there were on average 2.87 violent crimes per 10,000 inhabitants in the city of São Paulo and an average of 3.62 violent crimes per 10,000 inhabitants in the study area. While these numbers may be somewhat abstract, they imply that each person living in a densely populated area like the one studied - with an estimated density of 7770 inhabitants per km² - experiences, on average, 0.94 violent crimes per month within 1-km walking distance from home. This implies 5.6 crimes in close vicinity within the first six months of pregnancy for the average pregnant mother. Even mothers will, with all likelihood, personally witness only a small fraction of these events, the threat of external violence is, without any doubt, real and constantly present.

Second, our results suggest that external violence should not be interpreted as homogeneous characteristics of entire cities or larger census tracts, but something highly heterogeneous within relatively small spatial areas. As shown in Fig. 1, the distance between some of the safest and some of the most violent exposed neighborhoods is less than 2 km, highlighting the remarkable small scale at which urban disparities can be detected.

Third, and maybe most importantly, we found that exposure to crime is associated with substantial SGA, PT, and LBW increases even after controlling for SES status and maternal education, and other risk factors. Our findings that violence increases adverse birth outcomes are consistent with a previous municipality-level comparison from Brazil [27] and highlight the critical long-term consequences of violence beyond the immediate impact on the directly affected population. However, in their study, the authors found a pronounced difference among children of poorly educated mothers, suggesting that violence is only a component of the disadvantages that these children are exposed to due to low SES [27]. Similarly, another study found that neighborhood-level socio-economic-related risks directly affect LBW and PT, and these effects are mediated by personal-level risks such as SES status [17]. Despite the evidence, the pathways connecting neighborhood-level social and environmental conditions to individual-level adverse birth outcomes remain poorly understood. Differences in birth outcomes across different socioeconomic levels could be due to psychosocial stressors [17, 54], which could trigger adverse birth outcomes through a series of behavioral and neuroendocrinal interactions affecting the intrauterine environment [7, 15‐19, 21‐23, 55].

The general literature on violence exposure and birth outcomes has been more mixed with some studies such as Messer et al. [26], finding no associations with adverse birth outcomes and others such as Goin et al. [29], finding only an association between first-trimester exposure and SGA. While several theoretical mechanisms highlighted in the literature and introduction of this paper seem consistent with the results presented here, we do not have data to directly investigate mechanisms such as blood pressure increases [56] and anxiety [57] highlighted in the literature. HPA axis activation would be consistent with the PT delivery increase documented in several epidemiological studies [20‐22, 58, 59]. It is also possible that heightened maternal cortisol levels may lead to increased placental corticotrophin and prostanoid release. This can stimulate uterine contractions, induce preterm delivery [17, 20‐23], and cause intrauterine growth restriction [7]. Although placental enzymes protect the fetus from increased maternal cortisol levels in principle, animal studies suggest that prenatal stress can affect the placental activity and in utero enzyme expression [60, 61].

Our results corroborate the previous literature and add to the understanding of violence and its influence on health in a densely populated and heterogenous setting in an LMIC. Although our study did not explore the direct violence against pregnant women, previous findings suggest that domestic violence against pregnant women and mental disorders during pregnancy can have detrimental effects on birth outcomes in the Western Region of São Paulo [62]. The pathways between psychosocial stressors, like indirect and direct violence during pregnancy, and adverse birth outcomes, are poorly understood. Still, both negatively affect maternal and child health, possibly, by a common pathway.

Rapid rates of urbanization combined with increasing economic and gender inequalities are likely to trigger increased rates of violent crime and lead to a higher prevalence of risk factors in many settings, especially in areas where access to basic education and health care services remains limited [63, 64]. High violence rates may also endorse and strengthen social and cultural norms around masculinity and gendered power relationships [65]. Intersectoral strategies to decrease violence are urgently needed, and health programs must be improved to support victims of all kinds of violence.

The results presented in this paper suggest that living in a neighborhood with high rates of violent crime is associated with substantial increases in small-for-gestational-age, preterm and low birth weight births. Actions to improve neighborhood safety and to prevent violence could reduce inequalities among disadvantaged populations with likely substantial long-term benefits on population health and wellbeing.