Eligibility Criteria:
1. Inclusion criteria: pregnant women presented with physiological dyspnea.
2. Exclusion criteria:
1. Non physiological causes of dyspnea in pregnancy
* Cardiac: arrhythmia, constrictive pericarditis , pericardial effusion , coronary heart disease , congestive heart failure , intracardiac shunt , cardiomyopathy , valvular heart disease.
* Chest wall, pleura, lungs: bronchial asthma, bronchiectasis ,bronchiolitis ,chronic obstructive pulmonary disease, pulmonary emphysema, interstitial lung disease, sarcoidosis ,lung tumor narrowing or compressing the airways , pleural effusion , pulmonary right-to-left shunt , pulmonary hypertension ,elevated hemi diaphragm, phrenic nerve palsy, kyphoscoliosis
* CNS and neuromuscular: amyotrophic lateral sclerosis , mitochondrial disease polymyositis/ dermatomyositis
* Metabolic: renal failure , thyroid disease
* Head and neck : laryngeal tumor ,vocal cord paralysis , vocal cord dysfunction , tumor compressing the upper airways , tracheal stenosis , goiter
* Others: anemia , anxiety disorder, panic attacks, , ascites , obesity, abdominal wall hernia
2. Refusal to participate