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This common symptom can arise due to the normal respiratory adaptation to pregnancy, is gradual in onset and is usually noticed by the woman when she is talking or at rest. In normal pregnancy, there is a 40–50% increase in minute ventilation, mostly owing to an increase in tidal volume rather than respiratory rate and this leads to the subjective awareness of breathing. A mild, fully compensated respiratory alkalosis is therefore normal in pregnancy (see Table A5.1 in Appendix 5.1).

However, in any pregnant woman complaining of breathlessness the ‘red flag’ features (Table 5.2) must be sought during history taking and acted upon.

The differential diagnosis of breathlessness in pregnancy includes:

 Anaemia

 Respiratory causes: asthma, pneumonia, pneumothorax, pulmonary embolus, pulmonary oedema

 Cardiac causes: cardiomyopathy, pulmonary hypertension, valvular heart disease

 Amniotic fluid embolus

 Metabolic (e.g. diabetic ketoacidosis)

 Neuromuscular (e.g. myasthenia gravis)

Table 5.2 Red flag symptoms and signs

Source: Adapted from RCP (Royal College of Physicians). Acute Care Toolkit 15: Managing Acute Medical Problems in Pregnancy. London: RCP, 2019. © 2019 Royal College of Physicians

Breathlessness	Especially if:of sudden onsetworse on lying flatif associated with tachycardia, chest pain or syncoperespiratory rate >20SAO2 <94% or falls to <94% on exertion
Headache	Especially if:sudden onset/thunderclap or worst headache everheadache that takes longer than usual to resolve or persists for more than 48 hoursthere are associated fever, seizures, focal neurology, photophobia or diplopiait requires opioids
Chest pain	Especially if:pain severe enough to require opioidsradiates to arm, shoulder, back or jawsudden onset, tearing or exertional chest painassociated with haemoptysis, breathlessness, syncope or abnormal neurologyassociated with abnormal observations
Palpitations	Especially if:the woman has a family history of sudden cardiac deaththere is structural heart disease or previous cardiac surgeryassociated with syncopeassociated with chest painpersistent severe tachycardia
Pyrexia >38°C	Absence of pyrexia does not exclude sepsis, as paracetamol and other antipyretics may temporarily suppress the pyrexia; equally, absence of pyrexia in the presence of sepsis is worrying
Abdominal pain	That requires opioids (excluding contractions)Associated with diarrhoea and/or vomiting
Reduced or absent fetal movements or fetal heart rate
Uterine (excluding contractions) or renal angle pain or tenderness
Generally unwell especially if distressed and anxious	Signs of a deteriorating condition

It is important also to remember that because respiratory rate does not increase in normal pregnancy, a rise in respiratory rate will often be the subtle first sign of impending critical illness in pregnancy and should prompt a systematic ABCDE clinical assessment.