Singleton pregnancies in 2000-2015 in Kansas, US examined
Photo: iStock A recent study emphasised the significance of reducing exposure to air pollutants during pregnancy to prevent adverse effects of preterm birth, low birth weight and pregnancy complications. Preterm births increased a little above 7 per cent mark in 2015 compared to 2000, the research found.
The study, Effects of air pollution on adverse birth outcomes and pregnancy complications in the U.S. state of Kansas (2000–2015), was published in the journal Scientific Reports. The researchers looked at singleton (just one baby at a time) pregnancies in 2000-2015 in Kansas, United States.
The study looked at the links between three ambient air pollutants [nitrogen dioxide (NO2), fine particulate matter (PM) 2.5 and ozone (O3)], two birth outcomes (preterm birth and birth weight) and two pregnancy complications [Gestational diabetes mellitus (GDM) and gestational hypertension or (GH)].GDM and GH are the most prevalent maternal medical complications during pregnancy.
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The birth weight analysis was done for 5,54,787 births, whereas the preterm birth analysis was done for 596,926 births. The average preterm birth weight was 2,499.5 grammes in the cases studied compared to the average 3,410.9 grammes full-term birth weight, the analysis said.
Maternal and infant characteristics from birth records of preterm and full-term singleton births in Kansas with an estimated date of conception from January 1st, 2000, to December 31st, 2015
In the study period, NO2 and PM2.5 levels continued to decrease with time, but there was an increase in O3 levels. In the given exposure period, the correlations between these air pollutants remained between moderate and low, the paper stated.
In addition, daily ambient air pollution data was modelled and pollutant exposure was assessed separately. This was done throughout the pregnancy and each trimester. Additionally, single and multi-pollutant models were used to determine the relationship between the three pollutants and outcomes of interest.
Maternal characteristics like race, ethnicity, education, age, birth parity, smoking status and marital status were also analysed during the study. The socioeconomic status was estimated from the greenspace in the zip code where the mother resided at the time she was pregnant. The associated poverty data also served as part of the study process.
A higher interquartile range (IQR) of O3 exposure during the second or third trimester and throughout pregnancy was associated with an increased risk of preterm birth, according to the study. The odds ratio ranged from 1.04 to 1.05. Babies born to mothers who were exposed to higher levels of O3 during the second and third trimesters were 9.86 g lighter at birth on average.
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Mothers with exposure to NO2 during the second trimester were found to be more susceptible to having GDM, the study further found. Those with exposure to O3 in their first trimester were found to be more susceptible to having GH.
The assessment also emphasised the link between the living conditions of such mothers, their exposure to air pollution and health effects. Mothers who lived in areas with higher poverty levels had to suffer worse pregnancy complications and birth consequences in association to their exposure to air pollution. This, as per the study, indicated the protective effect of wealth. However, it also pointed out that consistent results could not be obtained while making observations across all pollutants and outcomes.
The study report throughout dubbed air pollution a risk factor behind low birth weight, preterm birth, GH and GDM, while pointing out the evidence on this association remains inconclusive and inconsistent, with conflicting findings.
It concluded that higher O3 exposure played a role in increasing the risk of lower birth weight, preterm birth, and GH. It also underlined the link between NO2 exposure and increased risk of developing GDM.
In contradiction to other studies and their expectations, this study did not observe any negative correlations between pregnancy, maternal outcomes and exposure to PM 2.5. It went to suggest this could be so with Kansas being a predominantly rural state with low levels of PM2.5 in general.
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While detailed, high-resolution air pollution data usage in the study served as a strength, it had a limitation — the non-inclusion of certain maternal level risk factors. These being illicit drug use, alcohol use and previous preterm birth.
According to the World Health Organization (WHO), globally prematurity is the leading cause behind the death of children aged below 5 years.
“Inequalities in survival rates around the world are stark. In low-income settings, half of the babies born at or below 32 weeks (two months early) die due to a lack of feasible, cost-effective care such as warmth, breastfeeding support and basic care for infections and breathing difficulties. In high-income countries, almost all these babies survive. Suboptimal use of technology in middle-income settings is causing an increased burden of disability among preterm babies who survive the neonatal period,” the WHO stated.
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