Breathing polluted air during pregnancy is not merely an environmental inconvenience — accumulating evidence suggests it meaningfully shapes birth outcomes in ways that ripple into infant health and lifelong development. A scoping review consolidating data across cohort studies, case-control studies, and meta-analyses offers one of the more structured mappings yet of how specific air pollutants interact with gestational biology.

Drawing on 20 studies identified across PubMed, Embase, and Web of Science — including four systematic reviews with meta-analyses — the review examined four primary pollutants: fine particulate matter under 2.5 micrometers (PM2.5), nitrogen dioxide (NO₂), ozone, and air quality index composites. Outcomes tracked included birth weight, preterm birth, stillbirth, neonatal mortality, congenital anomalies, and NICU admission. PM2.5 emerged as the most consistently implicated pollutant, associated with reduced birth weight and elevated preterm birth risk across multiple study designs. Nitrogen dioxide showed similar, if somewhat less uniform, associations with both outcomes. Exposure was primarily assessed by trimester or pregnancy average; preconception exposure windows were notably absent from the literature.

This review arrives at a moment when the epidemiology of environmental exposures is maturing rapidly. The PM2.5 signal is biologically plausible: ultrafine particles cross the placental barrier, triggering systemic inflammation and oxidative stress that can disrupt placental vascularization and fetal oxygen delivery. What remains poorly resolved is the dose-response curve and which trimester represents the highest-risk window — a gap this review explicitly flags. The absence of preconception exposure data is a meaningful limitation, since maternal inflammatory status before conception may prime placental development. As a scoping review rather than a formal meta-analysis, the work cannot generate precise risk estimates independently, and considerable heterogeneity across included studies limits direct comparison. Still, the convergence across study designs strengthens the biological credibility of the association and reinforces the case for air quality as a measurable, modifiable perinatal health determinant.