Breathlessness, or dyspnea, is a common and often distressing symptom experienced by many women during pregnancy. The multifaceted causes of breathlessness in this context can be attributed to a combination of physiological changes and pathological conditions. During pregnancy, significant alterations in the maternal body occur, including increased blood volume, shifts in hormonal levels, and mechanical compression from the enlarging uterus, all of which can affect respiratory function and lead to feelings of breathlessness (Muzaffar et al., 2022; Lee et al., 2017).

Physiological adaptations of the respiratory system begin early in pregnancy and usually manifest as increased tidal volume and respiratory rate. These adjustments serve to meet the augmented oxygen demands of both the mother and the developing fetus. However, by the third trimester, the displacement of the diaphragm by the expanding uterus can hinder normal lung expansion, resulting in increased work of breathing and potentially exacerbating dyspnea (Muzaffar et al., 2022; Lapinsky, 2017). Studies suggest that nearly 75% of pregnant women report some degree of exertional dyspnea, particularly within the first 30 weeks of gestation (Muzaffar et al., 2022), underscoring how prevalent this symptom is during pregnancy.

System / Parameter	Typical Change / Mechanism	Clinical Relevance
Blood Volume	↑ 30–50%	Can lead to “physiologic anemia” (dilutional ↓ Hb).
Cardiac Output	↑ 30–50% (due to ↑ stroke volume & heart rate)	May cause benign systolic murmur; can exacerbate underlying heart disease.
Heart Rate	↑ ~10–20 bpm	Mild tachycardia is common.
Systemic Vascular Resistance	↓ (progesterone-induced vasodilation)	Accommodates ↑ blood volume; may cause mild hypotension (especially supine).
Venous Return	↑ venous pressure in lower extremities (mechanical + hormonal factors)	Predisposes to varicose veins & edema.
Coagulation Factors	Overall ↑ (estrogen + progesterone effect)	Hypercoagulable state raises risk of thromboembolism (DVT, PE).
Tidal Volume	↑ 30–40%	Increases oxygenation for both mother and fetus.
Respiratory Rate / Drive	Alveolar ventilation ↑ via progesterone-induced ↑ CO₂ sensitivity (rate may be slightly ↑ or unchanged)	Mild respiratory alkalosis is common (↓ PaCO₂), often perceived as dyspnea.
Diaphragmatic Elevation	Uterus pushes diaphragm upward in later pregnancy	Decreases lung capacity, contributing to the sensation of breathlessness.
Oxygen Consumption	↑ 15–20%	Reflects higher metabolic demands of pregnancy.
Airway Resistance	↓ (smooth muscle relaxation by progesterone)	May benefit airflow; individual response varies in conditions like asthma.

Beyond these physiological changes, a variety of pathological conditions contribute to the incidence of dyspnea in pregnancy. Anemia, which is common among pregnant women, can diminish oxygen-carrying capacity and intensify breathlessness (Lee et al., 2017). Pregnancy also increases the risk of thromboembolic events, including pulmonary embolism, which can present with sudden-onset dyspnea and carries significant morbidity (Pawar et al., 2023). Additional complications, such as preeclampsia and peripartum cardiomyopathy, may manifest with respiratory symptoms due to pulmonary edema or cardiac compromise (Lapinsky, 2017; Hilman et al., 2023).

Category	Potential Causes	Key Points
Pulmonary	Asthma (new onset or exacerbation) Pneumonia (bacterial, viral [COVID-19, influenza], tuberculosis) Bronchitis Interstitial Lung Disease Acute Respiratory Distress Syndrome (ARDS) Pulmonary Edema (cardiogenic or non-cardiogenic) COVID-19	Asthma exacerbations are common due to hormonal changes; monitor peak flow. ICS/LABA are safe in pregnancy. Pneumonia severity (↑ in pregnancy); COVID-19 (↑ risk of hypoxic respiratory failure). Pulmonary edema may arise from preeclampsia, tocolytic therapy (e.g., terbutaline), or fluid overload. Low threshold for CXR/CTPA if infection or ARDS is suspected (radiation risk < diagnostic delay).
Pleural	Pleural Effusion Pneumothorax Hemothorax (rare)	Pneumothorax risk (↑ in pregnancy) due to mechanical diaphragmatic stress. Hemothorax may occur with trauma or coagulopathy (e.g., HELLP syndrome).
Vascular	Pulmonary Embolism (PE) Amniotic Fluid Embolism (AFE) Venous Air Embolism (rare) Pulmonary Hypertension	PE is the #1 cause of sudden dyspnea in pregnancy (risk ↑ fivefold). Use CTPA (not V/Q scan) for diagnosis. AFE: Sudden hypoxia, hypotension, DIC – treat as obstetric emergency. Pulmonary hypertension has high mortality; avoid delays in echocardiography.
Cardiogenic	Peripartum Cardiomyopathy Valvular Heart Disease (e.g., mitral stenosis) Congenital Heart Disease Arrhythmias (e.g., SVT, atrial fibrillation) Acute Coronary Syndrome (rare but ↑ with older maternal age)	Peripartum cardiomyopathy peaks in the last month/postpartum. Echocardiography is diagnostic (LVEF ↓ <45%). Valvular disease (e.g., mitral stenosis) may decompensate due to pregnancy’s ↑ hemodynamic demands. Arrhythmias: Palpitations + dyspnea warrant ECG.
Non-Cardiogenic	Anemia (iron deficiency, B12/folate deficiency) Thyroid Disorders (hyperthyroidism > hypothyroidism) Sepsis (e.g., pyelonephritis, chorioamnionitis) Anxiety/Panic Disorders Diabetic Ketoacidosis (DKA) Anaphylaxis (drug allergy, insect stings)	Anemia: Hb ↓ 11 g/dL in 1st/3rd trimesters; fatigue + exertional dyspnea. DKA: May occur in pre-existing or gestational diabetes (check ketones if hyperglycemic). Anaphylaxis: Treat with epinephrine (safe in pregnancy).
Other	Physiologic Dyspnea (progesterone-driven hyperventilation, diaphragm elevation) Obesity (BMI ≥30 worsens dyspnea) Musculoskeletal (rib cage expansion, costochondritis) Gastroesophageal Reflux Disease (GERD) Deconditioning	Physiologic dyspnea affects 60–70% of pregnancies; peaks in 3rd trimester (reassure if no red flags). GERD: Acid reflux may mimic dyspnea; trial antacids (e.g., omeprazole). Deconditioning: Common in sedentary individuals; encourage safe exercise.

In sum, the causes of breathlessness during pregnancy span a wide spectrum—from normal physiological changes to serious pathological conditions. Recognizing these diverse etiologies is essential to differentiate benign from concerning presentations of dyspnea, guide clinical evaluation, and ensure timely management. Consequently, healthcare providers must maintain a high index of suspicion for significant pathologies when assessing pregnant individuals who report breathlessness, particularly if there is a sudden change in symptoms or additional warning signs (Fakehi et al., 2021).

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