Before the First Breath: How Air Pollution may Affect Babies in the Womb
Source article: Khamirchi, R., Moslem, A., Agah, J., Pozo, Ó. J., Miri, M., & Dadvand, P. (2020). Maternal
exposure to air pollution during pregnancy and cortisol level in cord blood. The Science of the total
environment, 713, 136622. https://doi.org/10.1016/j.scitotenv.2020.136622
Excerpt: The effects of air pollution on the respiratory system have been widely studied. However, its impact on newborn health through in utero exposure has received far less attention. This article reports a possible association between PM2.5 exposure during pregnancy and cortisol levels in cord blood, a hormone directly linked to stress.
In the last years, urban growth in low-and middle-income countries has increased exposure to air pollution above World Health Organization standards. Air pollution, especially particulate matter (PM), has been linked to serious health problems, particularly for pregnant women and their babies. Studies show that exposure during pregnancy can raise the risk of low birth weight, preterm birth, developmental issues, and pregnancy complications.
This study examines whether long-term exposure to PM and traffic pollution during pregnancy affects cortisol levels in umbilical cord blood, as key stress hormone.
The Air Babies Breathe Before Birth
To better understand the findings, it was first important to consider the characteristics of the city where the mothers lived. The study was conducted in Sabzevar, an Iranian city with a predominantly arid climate. Dry and arid regions are known to have higher levels of airborne particulate matter, such as PM2.5 and PM10, partly due to low rainfall, frequent dust events, and limited natural removal of particles from the air. These environmental conditions can contribute to sustained exposure to air pollution, making this setting
particularly relevant for studying the potential health effects of particulate matter during pregnancy.
Mothers, Babies and the Air Around There
To determine the relation with pregnant woman and their babies health, mothers who had normal term pregnancy (37 to 42 weeks) and spontaneous vaginal delivery, were invited to participate. Moreover, those mothers did not have hypertension, diabetes and preeclampsia. All of those data are important in this kind of research because must be required control all the factors that can insert variability. For that, almost the same conditions in participants must required. Moreover, data of lifestyle factors and socio-demographic characteristics were collected by questionnaires, whereas, after delivery, PM were measured in cord blood.
Also, exposure assessment was performed by measuring air pollutants including PM1, PM2.5 and PM10, taking in count the residential address of each participant using special equipment.
Stress Hormone Signature at Birth
Participants had a mean age of 27 years and a mean body mass index (BMI) of 23.7 kg/m². Most had completed secondary school education. The median cortisol level measured in cord blood was 44 ng/mL. As mentioned previously, several factors can influence cortisol levels in newborns, including gestational age,
postnatal age, and perinatal stress. However, in this study, all cord blood samples were collected at birth and analyzed under similar conditions, which reduces variability related to timing.
Basal cortisol levels in newborns have been reported to range approximately between 10 and 100 ng/mL, suggesting that the levels observed in our sample fall within a physiologically expected range. Nevertheless, due to the limited number of studies evaluating cord blood cortisol in relation to air pollution exposure, direct comparisons remain dificult.
Previous research in adults has shown a positive association between air pollution exposure and cortisol levels, meaning that higher pollution levels are linked to higher stress hormone concentrations. However, in adults, many additional factors may influence cortisol levels.
For example, high temperatures may increase pollution levels and independently affect cortisol secretion. In such cases, the association may not be directly causal but influenced by external environmental factors.
Therefore, it is essential to consider potential confounding variables when interpreting associations between air pollution and cortisol levels. In the present study, the researchers, moreover, measured air pollution levels (PM1, PM2.5 and PM10) at 26 monitoring stations and also estimated pollution levels at the homes of pregnant women in the study. They also looked at how close the mothers lived to major roads and how much traffic was around their homes.
They found that the different types of air pollution were moderately to strongly related to each other.
Main Findings
Higher exposure to PM2.5 and PM10 during pregnancy was linked to higher cortisol levels in babies’ cord blood at birth.
More nearby streets within 100 meters of the home (which suggests more traffic) was also linked to higher cortisol levels. Living farther away from a major road was linked to lower cortisol levels in cord blood.
No clear link was found between PM1 or larger traffic areas (300 m and 500 m) and cortisol levels.
These results did not change even after considering other factors such as exposure to tobacco smoke, cooking habits, car ownership, newborn sex, or body mass index.
Also, as this was the firs study to examine whether air pollution during pregnancy is linked to cortisol levels in babies at birth, researchers make a strong discussion about the mechanistic explanation about the results.
Possible Ways Air Pollution Affects Newborn
There are several possible explanations. For example, air pollution may increase stress in the mother, raising her cortisol levels, which can then affect the baby. In addition, pollution may cause inflammation and oxidative stress, activating the body’s stress system (the HPA axis). Pollution may also affect the placenta, reducing its ability to block cortisol from reaching the baby. Furthermore, pollution particles might even directly affect the baby’s stress system. However, these mechanisms still require further research in humans.
At the same time, the researchers noted some limitations in the study: pollution exposure was estimated based only on the home address, without considering workplaces or other locations. Other pollutants that could also influence the results were not measured.
Maternal cortisol levels were not recorded. Additionally, some lifestyle factors, such as diet, stress, and physical activity, were not included.
Final Conclusions
Exposure to certain types of air pollution during pregnancy was linked to higher cortisol levels in newborns. If confirmed by future studies, these findings suggest that air pollution may affect babies before birth and highlight the importance of reducing pollution exposure during pregnancy
Reviewed by:
