Causal effects on low Apgar at 5-min and stillbirth in a malaria maternal–fetal health outcome investigation: a large perinatal surveillance study in the Brazilian Amazon

BACKGROUND: Malaria elimination in Brazil poses several challenges, including the control of Plasmodium falciparum foci and the hidden burden of Plasmodium vivax in pregnancy. Maternal malaria and fetal health outcomes were investigated with a perinatal surveillance study in the municipality of Cruzeiro do Sul, Acre state, Brazilian Amazon. The research questions are: what are the causal effects of low birth weight on low Apgar at 5-min and of perinatal anaemia on stillbirth? METHODS: From November 2018 to October 2019, pregnant women of ≥ 22 weeks or puerperal mothers, who delivered at the referral maternity hospital (Juruá Women and Children’s Hospital), were recruited to participate in a malaria surveillance study. Clinical information was obtained from a questionnaire and abstracted from medical reports. Haemoglobin level and presence of malarial parasites were tested by haematology counter and light microscopy, respectively. Low Apgar at 5-min and stillbirth were the outcomes analysed in function of clinical data and epidemiologic risk factors for maternal malaria infection using both a model of additive and independent effects and a causal model with control of confounders and use of mediation. RESULTS: In total, 202 (7.2%; N = 2807) women had malaria during pregnancy. Nearly half of malaria infections during pregnancy (n = 94) were P. falciparum. A total of 27 women (1.03%; N = 2632) had perinatal malaria (19 P. vivax and 8 P. falciparum). Perinatal anaemia was demonstrated in 1144 women (41.2%; N = 2779) and low birth weight occurred in 212 newborns (3.1%; N = 2807). A total of 75 newborns (2.7%; N = 2807) had low (< 7) Apgar scores at 5-min., and stillbirth occurred in 23 instances (30.7%; n = 75). Low birth weight resulted in 7.1 higher odds of low Apgar at 5-min (OR = 7.05, 95% CI 3.86–12.88, p < 0.001) modulated by living in rural conditions, malaria during pregnancy, perinatal malaria, and perinatal anaemia. Stillbirth was associated with perinatal anaemia (OR = 2.56, 95% CI 1.02–6.42, p = 0.0444) modulated by living in rural conditions, falciparum malaria during pregnancy, perinatal malaria, and perinatal fever. CONCLUSIONS: While Brazil continues its path towards malaria elimination, the population still faces major structural problems, including substandard living conditions. Here malaria infections on pregnant women were observed having indirect effects on fetal outcomes, contributing to low Apgar at 5-min and stillbirth. Finally, the utility of employing multiple statistical analysis methods to validate consistent trends is vital to ensure optimal public health intervention designs. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12936-021-03981-y.