Prenatal Ambient Air Pollution, Placental Mitochondrial DNA Content, and Birth Weight in the INMA (Spain) and ENVIRONAGE (Belgium) Birth Cohorts

BACKGROUND

Mitochondria are sensitive to environmental toxicants due to their lack of repair capacity. Changes in mitochondrial DNA (mtDNA) content may represent a biologically relevant intermediate outcome in mechanisms linking air pollution and fetal growth restriction.

OBJECTIVE

We investigated whether placental mtDNA content is a possible mediator of the association between prenatal nitrogen dioxide (NO2) exposure and birth weight.

METHODS

We used data from two independent European cohorts: INMA (n = 376; Spain) and ENVIRONAGE (n = 550; Belgium). Relative placental mtDNA content was determined as the ratio of two mitochondrial genes (MT-ND1 and MTF3212/R3319) to two control genes (RPLP0 and ACTB). Effect estimates for individual cohorts and the pooled data set were calculated using multiple linear regression and mixed models. We also performed a mediation analysis.

RESULTS

Pooled estimates indicated that a 10-μg/m3 increment in average NO2 exposure during pregnancy was associated with a 4.9% decrease in placental mtDNA content (95% CI: -9.3, -0.3%) and a 48-g decrease (95% CI: -87, -9 g) in birth weight. However, the association with birth weight was significant for INMA (-66 g; 95% CI: -111, -23 g) but not for ENVIRONAGE (-20 g; 95% CI: -101, 62 g). Placental mtDNA content was associated with significantly higher mean birth weight (pooled analysis, interquartile range increase: 140 g; 95% CI: 43, 237 g). Mediation analysis estimates, which were derived for the INMA cohort only, suggested that 10% (95% CI: 6.6, 13.0 g) of the association between prenatal NO2 and birth weight was mediated by changes in placental mtDNA content.

CONCLUSION

Our results suggest that mtDNA content can be one of the potential mediators of the association between prenatal air pollution exposure and birth weight.

CITATION

Clemente DB, Casas M, Vilahur N, Begiristain H, Bustamante M, Carsin AE, Fernández MF, Fierens F, Gyselaers W, Iñiguez C, Janssen BG, Lefebvre W, Llop S, Olea N, Pedersen M, Pieters N, Santa Marina L, Souto A, Tardón A, Vanpoucke C, Vrijheid M, Sunyer J, Nawrot TS. 2016. Prenatal ambient air pollution, placental mitochondrial DNA content, and birth weight in the INMA (Spain) and ENVIRONAGE (Belgium) birth cohorts. Environ Health Perspect 124:659-665; http://dx.doi.org/10.1289/ehp.1408981.

Socio-economic inequalities in health, habits and self-care during pregnancy in Spain

Socioeconomic disadvantage can be harmful for mother's health and can influence child's health long term. The aim of this study is to analyse social inequalities between pregnant women from four INMA (INfancia y Medio Ambiente) cohorts. The analysis included 2,607 pregnant women recruited between 2004 and 2008 from four INMA cohorts. Data on maternal characteristics were collected through two questionnaires completed in the first and third trimester of pregnancy. The relationship between socioeconomic status (SES) and maternal health, dietary intake, lifestyle habits and self-care related variables was modelled using logistic regression analysis. 33.5 % of women had a university level of education and 47 % had high occupational class. Women with higher SES reported healthier habits, fewer complications during pregnancy, better weight gain control and attended more prenatal appointments than women with lower SES. The risk of sedentary behaviour and passive smoking was higher among women with a lower level of education (OR = 1.7, 95 % CI 1.3-2.2 and OR = 1.6, 95 % CI 1.2-2.3, respectively) and with less skilled occupations (OR = 1.7, 95 % CI 1.4-2.0 and OR = 1.2, 95 % CI 1.0-1.5, respectively). Although both SES indicators-occupation and education-act as social determinants of diet, occupation was a more powerful determinant than education. For other lifestyle and self-caring variables, education was a more powerful predictor than occupation. Social inequalities were observed in health, habits and self-care during pregnancy. Proper care during pregnancy requires the control of common clinical variables and the knowledge of socioeconomic conditions of the pregnant women.