London (CNN) Scientists believe they have discovered the first examples of air pollution traveling through the lungs of pregnant women and into their placentas, potentially reaching their fetuses.

The study, presented at the European Respiratory Society International Congress in Paris, examined the placentas of five pregnant women in the United Kingdom and found that sooty particles had made their way into their placentas.

"We do not know whether the particles we found could also move across into the fetus, but our evidence suggests that this is indeed possible," Dr. Norrice Liu, a pediatrician and clinical research fellow at Queen Mary University in London who led the research, said in a statement.

"We also know that the particles do not need to get into the baby's body to have an adverse effect, because if they have an effect on the placenta, this will have a direct impact on the fetus."

The five pregnant women who took part in the study all lived in London and were scheduled to have planned cesarean section deliveries. All five were non-smokers and gave birth to a healthy baby after uncomplicated pregnancies.

Each of the women consented to having their placenta, an organ that attaches itself to the womb during pregnancy and links the mother to the fetus, examined by the research team.

The placenta allows oxygen and nutrients to pass through the mother's blood supply to the fetus through the umbilical cord and also ensures the disposal of any waste..

This particular study looked at placental macrophages. These cells are part of the body's immune system and tackle harmful particles such as bacteria and pollution particles, and are key in helping to protect the placenta.

According to the report, the team examined 3,500 macrophage cells from the five placentas, finding that 60 of the cells contained 72 dark areas between them, which the researchers believe were carbon particles.

"We've known for a while that air pollution affects fetal development and can continue to affect babies after birth and throughout their lives," said Dr. Lisa Miyashita, at Queen Mary University of London, who also presented the research.

"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."

Dr. Mina Gaga, president of the European Respiratory Society, added that "this new research suggests a possible mechanism of how babies are affected by pollution while being theoretically protected in the womb."

"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," she said in a statement.

The research is at an early stage, but the findings build on previous research highlighting links between the exposure of pregnant mothers to air pollution and infant mortality, premature birth and low birth weight.

"We have strong evidence that higher levels of road traffic air pollution in London are associated with higher risk of adverse pregnancy outcomes, such as babies born of low birthweight. This innovative research provides new insight into potential mechanisms to explain this association and further our understanding of causal pathways to disease," said Dr. Mireille Toledano, chair in Perinatal and Paediatric Environmental Epidemiology, at Imperial College London, who was not involved in the new research.

"It is clear that current regulatory air pollution levels are not sufficiently protecting pregnant women and their unborn babies and this needs to be urgently addressed by policy makers to improve public health."