Maternal Exhaled Carbon Monoxide Levels and Placental Histomorphological Alterations in an Urban Niger Delta Population, Nigeria

Abstract

Background: Carbon monoxide (CO) is a combustion-derived pollutant that reduces oxygen transport and may produce hypoxic stress during pregnancy. The placenta is central to maternal-foetal exchange and may show structural responses to environmental insults. However, evidence linking directly measured maternal CO exposure with placental histomorphological findings remains limited in the Niger Delta. Aim: This study aimed to assess the relationship between maternal exhaled CO levels and placental histomorphological characteristics among term deliveries. Methodology: This analytical cross-sectional study involved 240 pregnant women attending antenatal care at Rivers State University Teaching Hospital, Port Harcourt. Maternal CO exposure was assessed using a calibrated Smokerlyzer® CO monitor, which measured exhaled CO in parts per million and estimated carboxyhaemoglobin levels. Placentae were obtained from 69 term deliveries, and a systematically selected subset of 23 placentae underwent histological examination. Data were analysed with statistical significance set at p < 0.05. Results: All measured maternal CO values were within the low exposure range. Among the 23 examined placentae, 12 (52.2%) were histologically normal, while 11 (47.8%) showed dystrophic calcification of varying severity. Maternal CO concentration was not significantly associated with histomorphological classification (ρ = 0.004, p = 0.986). Placental weight, thickness, diameter, shape, cotyledon count and birth weight also showed no significant association with histomorphological category. Conclusion: Low-level maternal exhaled CO exposure was not associated with detectable placental histomorphological alterations in this cohort. The observed calcification may be more consistent with term placental ageing than exposure-related injury.