Wildfire smoke impacts pregnancy outcomes

Relation

Heft-Neal S, Driscoll A, Yang W, Shaw G, Burke M. Associations between wildfire exposure during pregnancy and risk of preterm birth in California.Environment Res. 2022;203:111872.

Study objective

To examine the effects of smoke exposure near wildfires during pregnancy on preterm births in California

Draft

Observational, prospective, fixed cohort study

Participant

Researchers initially limited the study to infants born in California between 2006 and 2011 at 23 to 41 weeks' gestational age (of which there were 3,493,242 births); however, based on the estimated conception dates, they only included 3,063,672 births in the present study to avoid fixed cohort bias. (Births occurring 23 weeks before October 2006 and after 41 weeks before December 31, 2012 were excluded from the study.)

Demographic data included maternal age, ethnicity, education, income, place of birth, parity, and history of cigarette use, as well as child sex and gestational age. Multiple births were excluded.

Study parameters assessed

Researchers pulled birth data from California Department of Public Health birth certificates for all 2,610 ZIP codes. They characterized exposure to wildfire smoke by the number of days that Hazard Mapping System (HMS) data correlated with the mother's zip code of residence during pregnancy, with the accumulation of weekly exposures assigned to weeks of pregnancy. Researchers assessed exposure for each trimester with periods differentiated weekly relative to the date of conception. Trimester 1 was characterized as weeks 1 to 13, trimester 2 as weeks 14 to 26, and trimester 3 as the last 4 weeks of pregnancy. Exposure for the entire third trimester was not assessed to avoid overlap in exposure before week 31.

The researchers measured the amount of particulate matter with diameters of less than 2.5 µm (PM_2.5) and other pollutants from wildfire smoke using an intensity metric with location data based on zip codes corresponding to bins 0-50, 50-75, and >75. percentile assigned at the grid cell level, and the timing of wildfire smoke. They used imaging from the National Oceanic and Atmospheric Administration (NOAA) to identify smoking days and calculated estimates of ground-level pollution using air quality sensors, satellite imagery and computer models of atmospheric motion.

An HMS detected smoke and fire activity. The researchers calculated cumulative exposure to different smoking intensities by dividing smoking days into different intensity classes. They took baseline air particles into account, so the difference between baseline and wildfire-related particle exposure was tracked (= anomalies). These were divided into 3 categories per day:

1. Niedrige Intensität: Tage mit PN_2.5 Anomalien <5 μg/m3
2. Mittlere Intensität: Tage mit PN_2.5 Anomalien 5–10 μg/m3
3. Hohe Intensität: Tage mit PN_2.5 Anomalien ≥10 μg/m3

Primary outcome measures

The researchers used multivariable analysis using covariates based on demographic characteristics (ethnicity, race, education, income, place of residence, and parity) that influence the risk of preterm birth (PTB) with exposure to wildfire smoke during pregnancy. This was done per trimester and PM_2.5Concentrations (low, medium, or high intensity) in mothers' residential zip code using generalized regression models.

Key insights

Within each zip code, there was an increase in preterm births as the number and intensity of smoking days increased from baseline. Unlike previous studies, these results were independent of race, income, or ethnicity.

PM_2.5

Exposure to particulate matter_2.5Moderate intensity smoke resulted in a 0.95% (95% Cl: 0.47%-1.42%) increase in PTB risk during PM_2.5High-intensity smoke exposure had a 0.82% (95% Cl: 0.41%-1.24%) increased risk. Smoking days for medium and high intensity PM_2.5were higher in both the 2nd and 3rd trimesters, with increased associated risks. PM_2.5Low-intensity smoke had a value of zero for the entire pregnancy.

In total

A total of 187,913 PTBs were due to exposure to wildfire smoke between 2007 and 2012. Additional exposure to wildfire smoke during pregnancy was associated with a 0.49% (95% Cl: 0.41%-0.59%) increase in PTB risk (<37 weeks). Smoking days during the 2nd trimester had the greatest impact, with additional smoking days resulting in a 0.83% (95% Cl: 0.71%-0.96%) increase in PTB risk compared to 0.68% (95% Cl: 0.49%). -0.87%) increase with third trimester exposure. The 1st trimester had a value of zero. During pregnancy, an additional day of smoking resulted in a 0.88% (95% Cl: 0.52%-1.24%) increase in PTB risk <32 weeks and a 0.55% (95% Cl: 0.051.15%) increase in PTB risk <28 weeks, with the 2nd trimester being more exposed to exposure than the 3rd trimester.

Practice implications

Air pollution is associated with a number of health risks.¹Fetal health may be affected by maternal exposure to PM_2.5in wildfire smoke, which contains thousands of chemicals, can lead to an increased risk of PTB, low birth weight and congenital anomalies.¹PM_2.5can cause a wide range of biological reactions because its tiny size means it passes directly through the lung tissue into the blood.¹Both pathways of oxidative stress and inflammation may play a role in influencing pregnancy outcome, as exposure to air pollution allows particles to cross the blood-brain barrier and the placental barrier.¹PTB has been found to occur in approximately 12% of pregnancies worldwide and is the predominant cause of neonatal morbidity and mortality.²

While relative rates of PTB did not differ between sociodemographic cohorts in this study, the baseline estimate of PTB among black mothers was at least 1/3 higher than the other groups (ie, absolute rate). Data shows that Black mothers have significantly higher rates of PTB compared to other races due to several factors, including differences in health care.³Those suffering from health inequalities need adequate health services to reduce environmental health risks as they are more vulnerable to pre-existing health problems. Other studies have found that exposure to a natural disaster before, during, or after pregnancy can cause maternal stress, which is linked to negative pregnancy outcomes.⁴This is consistent with the theory of developmental origins of health and disease, which suggests that much of the risk of disease experienced later in life is determined by gene-environment interaction at the time of fertilization, embryonic, fetal, and neonatal life stages.⁵Maternal health can also suffer from high levels of stress. Stress can have programming effects on the maternal hypothalamic-pituitary-adrenal axis, have effects on embryonic development, and has been linked to the development of gestational diabetes.⁴

Various therapies have been evaluated for the treatment of sarcopenia, although exercise appears to outperform all others.

Long-term exposure to air pollution can impair beta cell function and reduce insulin-dependent glucose absorption, leading to insulin resistance.⁶In a systemic review of air pollution in adults, an 8% to 10% increase at 10 μg/m was associated with diabetes³Increase in PM_2.5. or nitrogen dioxide.⁶Several studies found associations between PM exposure_2.5during pregnancy and gestational diabetes.⁶Pregnant women who smoke tobacco or live in a smoking household are at even greater risk for adverse pregnancy and fetal outcomes due to the compounding toxic effects of wildfires and tobacco smoke.⁷Tobacco smoke and bushfire smoke have similar components, both of which are detrimental to the mother's health.⁷

Several measures can be taken to reduce PTB. Maintaining a healthy lifestyle during pregnancy is crucial for proper fetal development. Eating a balanced diet with foods rich in critical nutrients is essential.⁸Adequate intake of micronutrients is important to support pregnancy and breastfeeding.⁸For example, folate before conception and in early pregnancy is essential to reduce the risk of congenital birth defects.⁹Nutrient requirements increase significantly during pregnancy, so supplementation with iron, B vitamins, iodine, and vitamin A may be warranted in women with lower micronutrient levels.⁹Adequate vitamin D is also important during pregnancy to maintain maternal calcium levels necessary for fetal bone development. Vitamin D deficiency can lead to low birth weight, neonatal hypocalcemia and heart failure.⁹Women who live in areas with limited sun exposure or have darker skin are at higher risk of vitamin D deficiency.⁹

Physical activity during pregnancy reduces the risk of obesity and gestational diabetes.⁸Intervention studies show that pregnant women who exercise for approximately 30 minutes per day have lasting benefits to maternal health and well-being.⁸Weight management and a healthy body mass index (BMI) are important during pregnancy because weight retention after birth increases the risk of high blood pressure, diabetes, and stillbirth in later pregnancies.⁹Eating fish and supplementing with omega-3 fatty acids reduce the risk of PTB before 34 weeks of pregnancy.⁹Other factors that improve maternal quality of life and outcomes include stress management, maintaining healthy sleep habits, modulating the microbiome, and avoiding alcohol.⁸