It's no secret that a mother's exposure to pollution can harm her unborn child. Studies have linked polluted air to many a health problem, including premature birth, low birth weight, and infant mortality as well as childhood obesity, high blood pressure, respiratory problems, and brain abnormalities.
Now, we might be closer to understanding why. For the very first time, researchers have found evidence that microscopic carbon particles find their way to the placenta.
The research was presented last week at the European Respiratory Society International Congress in Paris, France, by Norrice Liu, a pediatrician and clinical research fellow, and Lisa Miyashita, a post-doctoral researcher. Both are members of Professor Jonathan Grigg's research group at Queen Mary University of London.
The researchers came to this discovery after examining the placentas of five women post-birth. The women were non-smokers who had undergone a C-section and they each lived in London, a city so polluted that it breached its annual air pollution limit within the first month of 2018. (Believe it or not, this is an improvement on the previous year, which saw pollution exceed the annual limit after just five days.)
From these five placentas, the researchers identified 3,500 placental macrophage cells. These cells are responsible for swallowing toxic particles, whether it's bacteria or pollution, and can be found across the body – not just in the placenta.
It turned out, each placenta contained an average of roughly 5 square micrometers of a black substance the researchers believe to be carbon particles. In total, they singled out 60 cells with 72 small black areas across the five placentas.
"We've known for a while that air pollution affects fetal development and can continue to affect babies after birth and throughout their lives," Miyashita said in a statement.
"We were interested to see if these effects could be due to pollution particles moving from the mother's lungs to the placenta. Until now, there has been very little evidence that inhaled particles get into the blood from the lung."
Next, they studied two placentas in even greater detail with an electron microscope. They found more of the same black substance.
"We were not sure if we were going to find any particles and if we did find them, we were only expecting to find a small number of placental macrophages that contain these sooty particles," Lui explained.
"This is because most of them should be engulfed by macrophages within the airways, particularly the bigger particles, and only a minority of small-sized particles would move into the circulation."
With just five placentas, this was a relatively small study and it does not necessarily prove that the particles can move from the placenta to the fetus. However, the authors say that it could be possible and it would explain why air pollution can have such an adverse prenatal effect. What's more, they add, the particles don't necessarily have to enter the baby's body to cause a problem. They affect the placenta and that is enough to do harm.
"This should raise awareness amongst clinicians and the public regarding the harmful effects of air pollution in pregnant women," Mina Gaga, who is President of the European Respiratory Society and was not involved in the research, .
"We need stricter policies for cleaner air to reduce the impact of pollution on health worldwide because we are already seeing a new population of young adults with health issues."