Maternal Respiratory Adaptation Failure during Pregnancy: A Proposed Conceptual Model Integrating Pulmonary Function, Biomarkers, and Maternal–Fetal Outcomes – A Systematic Narrative Review

Pregnancy imposes a usually well-tolerated respiratory load; difficulty arises when pulmonary or vascular reserve is limited and normal compensation no longer meets maternal and fetal demands. This systematic narrative review, reported in accordance with Preferred Reporting Items for Systematic reviews and Meta-Analyses 2020, examined respiratory physiology, pulmonary disease, vascular and biomarker evidence, and maternal–fetal outcomes across PubMed/MEDLINE, PubMed Central, Embase, Scopus, Web of Science, and the Cochrane Library. Thirty-two studies met the eligibility criteria and were synthesized narratively because their populations, designs, exposures, and outcomes were too heterogeneous for quantitative pooling. The evidence base included observational and interventional studies alongside mechanistic, systematic, clinical, and narrative reviews. Normal pregnancy showed increases in respiratory drive, tidal volume, minute ventilation, and oxygen consumption, with reduced functional residual capacity and compensated respiratory alkalosis. Respiratory vulnerability was more apparent with asthma exacerbation, severe infection, acute respiratory failure, pulmonary vascular disease, and hypertensive disorders. Pulmonary hypertension was particularly relevant as a model of restricted cardiopulmonary reserve. Angiogenic and endothelial markers, notably soluble fms-like tyrosine kinase-1 and placental growth factor, were reported mainly in preeclampsia; therefore, their relationship with respiratory compromise remains indirect and should not be interpreted as validated respiratory biomarkers. On this basis, we propose Maternal Respiratory Adaptation Failure as a preliminary, hypothesis-generating conceptual model, not a recognized diagnosis or validated syndrome. This review represents an initial evidence-mapping step in our work to assemble data across pulmonology and obstetrics. Prospective primary studies are now needed to test the model, define measurable thresholds, and determine whether integrated physiologic, pulmonary vascular, and biomarker assessment can predict maternal–fetal outcomes.