Maternal exposure to polycyclic aromatic hydrocarbon (PAH) and its effects on pregnancy outcomes: a systematic review

Background: In the natural environment, polycyclic aromatic hydrocarbons (PAHs) are predominantly associated with fine particulate matter (PM2.5) suspended in the ambient air. These tiny particles can be inhaled by humans and subsequently deposited in the respiratory system, where they can penetrate the bloodstream and accumulate in target organs, including the placenta. This condition resulted in placental dysfunction, which can lead to adverse pregnancy outcomes. Therefore, this study aims to systematically review the scientific published articles on maternal exposure towards PAHs during pregnancy and the effect on adverse pregnancy outcomes. Methods: This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A systematic article search was performed using three online databases: PubMed, Scopus, and ProQuest to identify articles published from 2000 to 2022. A thorough article search identified eight studies suitable for inclusion in this review, as well as two additional studies discovered through the snowballing technique. All the included studies underwent quality assessment by using the NIH quality assessment tool. Results: A total of 948 articles were screened, of which ten full-text articles met the inclusion criteria for final evaluation. The most frequently reported adverse pregnancy outcomes across the selected studies were fetal growth restriction, including reduced birth weight and birth length, decreased head circumference, small for gestational age (SGA) and preterm delivery. PAH-DNA adducts in the cord blood were significantly associated with prenatal exposure to PAHs. PAHs exposure appears to have the most adverse impact on embryonic development during the first trimester. Seven articles recorded high quality (score range from 11 to 12.5 points) and only three articles recorded fair quality (score range from 8.5 to 10.5 points). Conclusion: Our findings indicate that maternal exposure to PAHs could negatively impact pregnancy outcomes. While this review enhances the understanding of the observed relationship, only a limited number of studies have explored the underlying biological mechanism. The appropriate measures to protect and limit the maternal exposure to PAHs, particularly in the first trimester, must be implemented. These include providing clinical advice to the expectant mothers on reducing exposure to tobacco smoke and poor air quality, encouraging appropriate dietary modifications, as well as reinforcing governmental efforts to strengthen environmental regulations.