Background: Inhaling fine particles (particulate matter with diameter ≤ 2.5 μm; PM2.5) can induce oxidative stress and inflammation, and may contribute to onset of preterm labor and other adverse perinatal outcomes. Objectives: We examined whether outdoor PM2.5 was associated with adverse birth outcomes among 22 countries in the World Health Organization Global Survey on Maternal and Perinatal Health from 2004 through 2008. Methods: Long-term average (2001–2006) estimates of outdoor PM2.5 were assigned to 50-km–radius circular buffers around each health clinic where births occurred. We used generalized estimating equations to determine associations between clinic-level PM2.5 levels and preterm birth and low birth weight at the individual level, adjusting for seasonality and potential confounders at individual, clinic, and country levels. Country-specific associations were also investigated. Results: Across all countries, adjusting for seasonality, PM2.5 was not associated with preterm birth, but was associated with low birth weight [odds ratio (OR) = 1.22; 95% CI: 1.07, 1.39 for fourth quartile of PM2.5 (> 20.2 μg/m3) compared with the first quartile (< 6.3 μg/m3)]. In China, the country with the largest PM2.5 range, preterm birth and low birth weight both were associated with the highest quartile of PM2.5 only, which suggests a possible threshold effect (OR = 2.54; CI: 1.42, 4.55 and OR = 1.99; CI: 1.06, 3.72 for preterm birth and low birth weight, respectively, for PM2.5 ≥ 36.5 μg/m3 compared with PM2.5 < 12.5 μg/m3). Conclusions: Outdoor PM2.5 concentrations were associated with low birth weight but not preterm birth. In rapidly developing countries, such as China, the highest levels of air pollution may be of concern for both outcomes. Citation: Fleischer NL, Merialdi M, van Donkelaar A, Vadillo-Ortega F, Martin RV, Betran AP, Souza JP, O´Neill MS. 2014. Outdoor air pollution, preterm birth, and low birth weight: analysis of the World Health Organization Global Survey on Maternal and Perinatal Health. Environ Health Perspect 122:425–430; http://dx.doi.org/10.1289/ehp.1306837

Objective To test the hypothesis that a relative deficiency in L-arginine, the substrate for synthesis of the vasodilatory gas nitric oxide, may be associated with the development of pre-eclampsia in a population at high risk. Design Randomised, blinded, placebo controlled clinical trial. Setting Tertiary public hospital in Mexico City.Participants Pregnant women with a history of a previous pregnancy complicated by pre-eclampsia, or pre-eclampsia in a first degree relative, and deemed to be at increased risk of recurrence of the disease were studied from week 14-32 of gestation and followed until delivery.Interventions Supplementation with a medical food—bars containing L-arginine plus antioxidant vitamins, antioxidant vitamins alone, or placebo—during pregnancy. Main outcome measure Development of pre-eclampsia/eclampsia. Results 222 women were allocated to the placebo group, 228 received L-arginine plus antioxidant vitamins, and 222 received antioxidant vitamins alone. Women had 4-8 prenatal visits while receiving the bars. The incidence of pre-eclampsia was reduced significantly (χ2=19.41; P<0.001) in women randomised to L-arginine plus antioxidant vitamins compared with placebo (absolute risk reduction 0.17 (95% confidence interval 0.12 to 0.21). Antioxidant vitamins alone showed an observed benefit, but this effect was not statistically significant compared with placebo (χ2=3.76; P=0.052; absolute risk reduction 0.07, 0.005 to 0.15). L-arginine plus antioxidant vitamins compared with antioxidant vitamins alone resulted in a significant effect (P=0.004; absolute risk reduction 0.09, 0.05 to 0.14).Conclusions Supplementation during pregnancy with a medical food containing L-arginine and antioxidant vitamins reduced the incidence of pre-eclampsia in a population at high risk of the condition. Antioxidant vitamins alone did not have a protective effect for prevention of pre-eclampsia. Supplementation with L-arginine plus antioxidant vitamins needs to be evaluated in a low risk population to determine the generalisability of the protective effect, and the relative contributions of L-arginine and antioxidant vitamins to the observed effects of the combined treatment need to be determined.Trial registration Clinical trials NCT00469846.