Published in PLOS One on 2026-09-02, this study is presented as an attributed evidence briefing. The excerpts below are the original researchers’ words, reproduced under their Creative Commons Attribution licence. Health Signal has selected the abstract and, where needed, opening background paragraphs; the complete methods, results, limitations and references remain in the linked paper.
Original authors: Projestine Muganyizi, Amy Brenner, Aasia Kayani, Eni Balogun, Folasade Adenike Bello, Gibson Kagaruki, Haleema Shakur-Still, Ian Roberts, Kiran Javaid, Mwansa Ketty Lubeya, Oladapo Olayemi, Rizwana Chaudhri, Raoul Mansukhani, Vwalika Bellington, Gizachew Tiruneh
Source: PLOS One • DOI 10.1371/journal.pone.0357033
Read the complete primary study ↗ · Creative Commons Attribution licence
From the researchers
Abstract
High residential altitude is associated with adverse pregnancy outcomes, yet most research has focused on elevations above 2500 meters. There is limited evidence on how altitude impacts maternal health below this threshold, where 99% of the global population resides. We investigated the effect of mid-altitudes on maternal outcomes among women with moderate to severe anemia who delivered in hospitals in four sub-Saharan and Asian countries.
We analysed data from the World Maternal Antifibrinolytic-2 (WOMAN-2) trial, which recruited anaemic women admitted for vaginal delivery across 42 hospital sites in Nigeria, Pakistan, Tanzania, and Zambia. We compared women in mid-altitudes (1,000–2,499 m) with those at low-altitudes (< 1,000 m) using postpartum blood loss as the primary outcome. The key secondary outcome was clinical postpartum haemorrhage (PPH). Additional secondary outcomes included prenatal maternal health indicators (gestational age at labor onset, hypertensive disorders of pregnancy, baseline hemoglobin, severe anemia, and mean arterial pressure [MAP]), as well as intrapartum intervention indicators (assisted delivery, use of medical pain control, and use of oxytocin in labor). We used STATA version 18 for data analysis. We used classical logistic and modified Poisson regressions with cluster-robust standard errors to estimate the odds and risk ratios (RR) for dichotomous outcomes and linear regression with cluster-robust variance to estimate the β coefficients for the continuous outcomes.
Of 15,068 women, 4801 (31.9%) delivered at mid-altitude and 10,267 (68.1%) at low-altitudes. Delivery in mid-altitudes did not independently affect postpartum blood loss (β = 37.89 mL; 95% CI: −26.83–102.62), p = 0.243. Mid-altitude delivery compared to low-altitude was independently associated with a 22% lower risk of preterm delivery (aRR = 0.78; 95%CI: 0.73–0.83), p < 0.001, and a 26% lower risk of severe anaemia (aRR = 0.74; 95% CI: 0.68–0.82), p < 0.001. The use of medical pain control was 2.2 times higher (aRR = 2.20; 95% CI: 2.02–2.40), p < 0.001, and the Odds of assisted delivery were 46% more likely (aOR = 1.46; 95% CI: 1.20–1.78) at mid-altitudes compared to low-altitudes.
Delivery at mid-altitudes was not independently associated with postpartum blood loss, but generally exhibited more favorable prenatal maternal health indicators and more intrapartum interventions than those delivering at low-altitudes.
Introduction
High altitude has been associated with negative pregnancy outcomes [1–4]. A systematic review and meta-analysis by Grant et al. analyzed 59 studies involving 1,604,770 pregnancies at altitudes of 2500 meters or higher and found increased odds of low birth weight, small for gestational age, and preterm birth [1]. Another review focusing on maternal blood pressure at high altitudes (above 2500m) found that blood pressure, including gestational hypertension (but not preeclampsia), was higher compared to lower altitudes [3]. Many studies link these adverse outcomes to the body’s adaptation to chronic hypoxia and low barometric pressure at high elevations [4–8]. While fewer studies have explored the effects on maternal health specifically, some report increased maternal morbidity and mortality above 2500m, including hypertensive disorders of pregnancy, obstetric hemorrhage, and sepsis [3,7]. Other complications include polycythemia and related heart and lung issues, along with higher mortality [6,8–10].
Reading this evidence
Use the full paper to check the study design, participant selection, comparator and outcome definitions before drawing a practical conclusion. An association does not by itself show cause and effect. A reported performance measure needs its denominator and uncertainty. A finding from a particular facility, sample or time period should retain that scope when it is discussed elsewhere.
This briefing makes the source accessible within the wider hospital systems desk. It does not assess an individual patient or certify a product. When considering relevance to another health system, examine the original authors’ account of context and limitations, then seek local implementation evidence. The related reporting below provides other studies to read alongside this one; it is a topic connection, rather than a claim that their results are directly comparable.
© 2026 Projestine Muganyizi, Amy Brenner, Aasia Kayani, Eni Balogun, Folasade Adenike Bello, Gibson Kagaruki, Haleema Shakur-Still, Ian Roberts, Kiran Javaid, Mwansa Ketty Lubeya, Oladapo Olayemi, Rizwana Chaudhri, Raoul Mansukhani, Vwalika Bellington, Gizachew Tiruneh. Excerpts reproduced under CC BY. Selection, formatting and contextual notes by Health Signal. The researchers are the authors of the source study, not members of Health Signal’s staff.
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