Abstract

Background: Pregnant women in Sub-Saharan Africa (SSA) live in settings where mining, oil extraction, informal industry and agriculture contaminate water, soil and food with toxic metals. Lead, mercury, cadmium and arsenic can cross the placenta and harm the mother and the developing fetus, yet exposure is rarely assessed in antenatal care.

Purpose: To identify the predominant heavy metals in maternal and neonatal samples in SSA, and to examine maternal-to-child transmission and the associated maternal and neonatal outcomes.

Methods: A systematic review was conducted following PRISMA 2020. Seven databases, grey literature and reference lists were searched for studies of pregnant women or mother-newborn pairs in SSA with maternal or neonatal metal measurements. Study quality was appraised with the Newcastle-Ottawa Scale, Joanna Briggs Institute checklists and AMSTAR-2, and findings were synthesised narratively.

Results: Thirty studies from 870 records were included. Lead was the most frequently reported and elevated metal; maternal blood lead ranged from 5.8 to 59.5 µg/dL. Cord-to-maternal lead ratios were 0.68 to 0.85. Mercury and arsenic showed ratios at or above 1.0 in several studies, whereas cadmium was partly retained by the placenta. Higher burdens were associated with low birth weight (11% to 32% in high-exposure groups), preterm birth, spontaneous abortion, preeclampsia, gestational hypertension and anaemia. Confidence in individual effect estimates was moderate to low, but confidence that exposure is widespread and clinically important was high.

Conclusion: Maternal-to-child transmission of toxic metals is common in SSA and is linked to outcomes that nurses and midwives manage daily. Exposure history-taking, counselling, monitoring and referral can be incorporated into antenatal nursing practice now, while prospective cohort research is urgently needed in South-East Nigeria.