Anemia: Given the increased blood volume and demands of pregnancy, anemia is a common condition that can lead to shortness of breath due to reduced oxygen-carrying capacity of the blood.

Asthma: Pre-existing asthma can worsen during pregnancy due to hormonal changes and increased blood volume, leading to bronchospasm and shortness of breath.
Pulmonary Embolism (PE): Although more commonly associated with the postpartum period, PE can occur during pregnancy due to hypercoagulability and venous stasis, causing sudden onset of shortness of breath.
Gestational Hypertension/Preeclampsia: These conditions can lead to pulmonary edema, resulting in shortness of breath.
Respiratory Infections: Such as pneumonia, which can be more severe during pregnancy due to the altered immune state.

Pulmonary Embolism (PE): As mentioned, while also listed under other likely diagnoses, it's crucial to not miss PE due to its high mortality rate if untreated.
Amniotic Fluid Embolism (AFE): A rare but catastrophic condition where amniotic fluid enters the maternal circulation, causing a severe reaction that can lead to respiratory distress.
Cardiac Conditions: Such as peripartum cardiomyopathy or worsening of pre-existing heart disease, which can present with shortness of breath and are critical to diagnose promptly.

Idiopathic Pulmonary Arterial Hypertension (IPAH): A rare condition characterized by elevated pulmonary artery pressure without a clear cause, which can worsen during pregnancy.
Lymphangioleiomyomatosis (LAM): A rare lung disease that can cause shortness of breath and is more commonly diagnosed in women of childbearing age.
Cystic Fibrosis: A genetic disorder that can lead to respiratory complications, including shortness of breath, and may first be diagnosed or worsen during pregnancy.