Parental preconception exposure to residential outdoor neighbourhood environments and adverse pregnancy and birth outcomes: a scoping review

Background: Preconception exposure to residential outdoor neighbourhood environments can influence perinatal outcomes by influencing fertility, gamete quality and foetal development through mechanisms such as oxidative stress, epigenetics and inflammation. Following our published protocol, this scoping review aims to synthesize the available evidence and identify gaps in the current understanding of this topic. Methods: We searched four databases (Cumulative Index to Nursing and Allied Health Literature, Ovid Medline, Ovid Embase and Scopus) for peer-reviewed publications on 20 December 2023. The search was restricted to English, without other restrictions. Two reviewers independently screened titles, abstracts and full texts. Findings were narratively synthesised. Results: We identified 82 eligible studies since 2010, all but one from upper-middle-or high-income countries. The largest proportion (43%) comprised retrospective cohort studies, with number of studies published since 2020 trending upwards. Although preconception was usually defined as the three months before pregnancy, most studies assigned these exposures using pregnancy or birth addresses, assuming residential stability since preconception. Among included studies, exposure to PM2.5 was associated with an increased risk of gestational diabetes mellitus (GDM), while PM10 was linked to birth defects. However, most exposure-outcome associations were inconsistent across included studies. The literature suggested the strongest consistency for PM10-birth defects associations, while evidence for O3-GDM associations was inconclusive. Research on other outdoor environmental factors, such as noise, light pollution, weather, built and natural environments, was lacking. Conclusions: Our review found that the existing evidence base is geographically skewed, concentrated on air pollution exposures, and notably lacking in research on paternal exposures. To advance the field, future studies should adopt more precise exposure assessments and expand the range of environmental factors, geographical diversity, and paternal exposure research.