Interaction of PM2.5 and pre-pregnancy body mass index on birth weight: A nationwide prospective cohort study

Abstract

BackgroundFine particulate matter (PM2.5), one of the most common air pollutants worldwide, has been associated with many adverse birth outcomes in some studies. Pre-pregnancy body mass index (BMI) is an important indicator of maternal obesity that may also contribute to a wide range of birthweight outcomes. Both PM2.5 and maternal obesity have been found associated with issues on neonatal birthweight respectively, and more attentions and interests are focusing on their combined effect on pregnancy outcomes.PurposeTo explore the modifying effect of pre-pregnancy BMI on the association between gestational PM2.5 and birthweight; to investigate the interactive effect between gestational PM2.5 and pre-pregnancy BMI on birthweight among pregnant women during three trimesters and the whole pregnancy.MethodsThis nationwide cohort study used the National Free Preconception Health Examination Project (NFPHEP) data collected from January 1, 2010, to December 31, 2012. A total population of 248,501 Chinese women from 220 counties registered this project. Pre-pregnancy BMI as a common anthropometric examination was collected during preconception investigation, and gestational PM2.5 was derived from a hindcast model for historical PM2.5 estimation from satellite-retrieved aerosol optic depth. Subgroup analysis was conducted to explore a potential modifying effect on the association between PM2.5 and birthweight during pregnancy by four pre-pregnancy BMI subgroups. Interaction analysis by introducing product terms to multivariable linear regression was also used to examine whether there was an interactive relationship between PM2.5 and pre-pregnancy BMI.ResultsTotally, 193,461 participants were included in our study. The average concentration of PM2.5 was 75.33 μg/m3. Higher exposure of PM2.5 during the entire pregnancy was associated with higher birthweight (17.15 g per 10 μg/m3; 95% CI:16.15, 18.17). Each 10 μg/m3 increase in PM2.5 during the first, second, and third trimesters was associated with increases in birthweight by 14.93 g (95%CI: 13.96, 15.89), 13.75 g (95% CI: 12.81, 14.69), and 8.79 g (95% CI: 8.09, 9.49), respectively. Higher pre-pregnancy BMI per kg/m2 was associated with an increase of birthweight by 7.012 g (95% CI: 6.121, 7.902). Product terms between PM2.5 and pre-pregnancy BMI were significant for the first, second trimesters, and the entire duration of pregnancy.ConclusionsOur results found both gestational PM2.5 exposure and pre-pregnancy BMI respectively correlated with the increase of birthweight. A negative interaction between pre-pregnancy BMI and gestational PM2.5 was discovered in term of birthweight gain. Avoidance of high-dose exposure to PM2.5 during the early and middle stages of pregnancy and pre-pregnancy overweight/obesity may help prevent high birthweight.

Association of Fine Particulate Matter and Its Components with Macrosomia: A Nationwide Birth Cohort Study of 336 Chinese Cities

“…Consistent with our results, a previous cohort study found a negative interaction effect between the prepregnancy BMI and PM 2.5 exposure. Specifically, the study found that a larger maternal BMI may offset the effects of PM 2.5 exposure on birth weight gain . One possible reason might be that overweight women may be more inclined to carefully control their intake to maintain the health of the infant.…”

“…Specifically, the study found that a larger maternal BMI may offset the effects of PM 2.5 exposure on birth weight gain. 64 One possible reason might be that overweight women may be more inclined to carefully control their intake to maintain the health of the infant. Additionally, the associations between PM 2.5 and macrosomia risk might be confounded by other factors among overweight women, such as the use of medicine.…”

Association between hypoproteinaemia with massive proteinuria and small for gestational age in pre-eclampsia: a single-centre, retrospective cohort study using propensity score matching

“…Propensity score matching expresses the influence of multiple confounding factors as a comprehensive propensity score to equalise the differences in baseline characteristics between the two groups and weaken the influence of covariates on effect estimation. A series of studies4 25–28 have shown that maternal risk factors, including maternal BMI, gestational weight gain, diabetes mellitus, chronic hypertension, maternal thyroid function and anaemia, can negatively influence fetal growth. These aforementioned maternal factors affecting birth weight and gestational age at diagnosis and delivery were matched using propensity scores.…”