Air pollution can affect the development of unborn babies in the womb.
Air pollution affects the thyroid, according to scientists from the UPV/EHU-University of the Basque Country, as small particles like nitrogen dioxide and carbon can impact the levels of thyroxine, a key thyroid hormone.
Thyroid hormones are essential for regulating foetal growth and metabolism, and play an important role in neurological development.
"In this work, we specifically analysed the effect of maternal exposure to these fine particles and to nitrogen dioxide during pregnancy and the link existing with thyroxine levels in newborn babies," explained Amaia Irizar-Loibide, a researcher in the UPV/EHU's Department of Preventive Medicine and Public Health.
"We have been monitoring on a weekly basis, as the development of the foetus varies greatly from one week to the next. So, we tried to conduct the most detailed research possible in order to find out which the most sensitive weeks of pregnancy are."
Strangely, the scientists found that air pollution affects thyroxine in different ways at different stages of pregnancy - with it lowering levels in the early stages, but raising it later when carrying a baby.
"The results obtained in this study have revealed the direct relationship between exposure to fine particles during pregnancy and the level of thyroxine in newborns," Irizar-Loibide stated. "However, we have not observed a clear link with exposure to nitrogen dioxide.
"What we have seen in this work is that exposure during the first months of pregnancy has a direct influence on the balance of thyroid hormones. These babies tend to have a lower level of thyroxine.
"As the pregnancy progresses, we found that this relationship gradually diminishes, i.e. the mother's exposure gradually becomes less important.
"In late pregnancy, however, this link becomes apparent again, but displays an opposite effect: as the concentration of these fine particles increases, we have seen that the level of thyroid hormones also increases, which has the opposite effect on the balance."
As the UPV/EHU team are unclear as to the biological mechanism behind these changes, they now want to conduct further research into the topic.
"We need to continue to investigate whether exposure during pregnancy affects not only thyroid hormones, but also other aspects such as neuropsychological development, growth, obesity, etc.," Irizar-Lobide added.