Air pollution may raise intrahepatic cholestasis of pregnancy risk
Black carbon emerged as PM2.5 constituent risk through second trimester
Exposure to high levels of fine particulate matter, or PM2.5, the most commonly studied air pollutant, and reduced time in the sunlight in the three months before pregnancy may increase the risk of developing intrahepatic cholestasis of pregnancy (ICP).
That’s according to a large study in China that also showed that regarding different constituents of PM2.5, exposure to high levels of organic matter during the first trimester and to black carbon during the first and second trimesters also increased ICP risk.
“Women preparing to conceive should increase sunlight exposure and avoid exposure to air pollution,” the researchers wrote.
The study, “Associations between fine particulate matter and its constituents and intrahepatic cholestasis of pregnancy,” was published in Ecotoxicology and Environmental Safety.
Cholestasis occurs when the bodily fluid bile doesn’t flow properly from the liver to the intestines, where it helps digest food. This causes bile acids, the main component of bile, to build up in the liver and leak into the bloodstream, leading to a range of symptoms. ICP is a form of cholestasis that develops in pregnancy, usually in the second or third trimester. While it typically resolves after childbirth, it increases the risk of complications for mothers and their babies. The exact causes of ICP are unclear, but they may involve a combination of factors, including environmental ones.
Pregnant women may breathe in more air pollutants because their bodies need more oxygen and have increased blood flow, the researchers said. These pollutants can also pass into their baby’s bloodstream, which can harm their health as they grow in the womb and after birth.
Effects of constituents of PM2.5
Researchers in China previously showed that exposure to higher PM2.5 levels and reduced sunlight duration in the three months before pregnancy increased the risk of ICP, but an “in-depth analysis of the correlation between ICP and different constituents of PM2.5” remained to be completed, the researchers wrote.
PM2.5 is a type of air pollution made of particles smaller than 2.5 micrometers — about 30 times thinner than a human hair — that can reach deep into the lungs and even enter the bloodstream, posing risks to health. Common sources of it include car exhaust, factories, wildfires, and burning wood or coal.
To understand how specific PM2.5 constituents, as well as sunlight duration, before and during early pregnancy, affect ICP risk, the researchers examined data from 160,544 women (mean age, 30.8), who gave birth between 2014 and 2020 at two Chinese hospitals. Daily PM2.5 levels in the air were collected for each woman’s residential address and sunlight duration was assessed using meteorological data.
A total of 1,333 women were diagnosed with ICP. It was more common for those with ICP to have multiple pregnancies, preterm birth (before 37 weeks of gestation), and pregnancy-related diabetes and high blood pressure over those without ICP. Also, a higher percentage of women with ICP conceived through assisted reproductive technology — which allows pregnancy when it may not otherwise be possible, such as in cases of infertility — and had cesarean sections.
Our in-depth analysis findings could help policymakers improve the air quality of residential areas and provide recommendations for women who are preparing to become pregnant to increase sunshine exposure and avoid exposure to air pollution.
Each PM2.5 increase of 10 micrograms per cubic meter in the three months before pregnancy was significantly associated with a 17.6% higher risk of ICP, results showed.
The risk also increased with specific PM2.5 constituents, such as sulfate, organic matter, and black carbon, which had the greatest impact. Specifically, an increase of 1 microgram per cubic meter of black carbon was significantly linked to a 27.4% higher ICP risk.
Also, every hour reduction in sunlight exposure before pregnancy had a 21.3% higher risk, a significant association.
During the first trimester of gestation, for each increase of 1 microgram per cubic meter of organic matter and black carbon, the risk of ICP increased by 4.3% and 20.1%, respectively. In the second trimester, an increase of 1 microgram per cubic meter of black carbon was significantly associated with a 27.8% higher risk, making it “the only constituent of PM2.5 that was positively associated with ICP from preconception to the second trimester.”
Further analyses showed that before a pregnancy, exposure to higher levels of PM.2.5 — and specifically sulfate, organic matter, and black carbon — appeared to interact with limited sunlight to increase the risk of ICP. No such interactions were found in the early stages of pregnancy.
“Our in-depth analysis findings could help policymakers improve the air quality of residential areas and provide recommendations for women who are preparing to become pregnant to increase sunshine exposure and avoid exposure to air pollution,” the researchers wrote.
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