Differential Diagnosis of Migraine in the Third Trimester

Single Most Likely Diagnosis

• Tension Headache: This is often considered due to the physical and emotional stress associated with the third trimester of pregnancy. However, the presentation of migraine itself, if the patient has a history of migraines, remains a strong candidate for the single most likely diagnosis, especially if the headache characteristics align with the patient's previous migraine episodes.

Other Likely Diagnoses

• Preeclampsia: A condition characterized by high blood pressure and often accompanied by protein in the urine, occurring after the 20th week of pregnancy. Headache can be a symptom, and it's crucial in the differential due to its implications for both mother and fetus.
• Sinusitis: Inflammation of the sinuses can cause headaches that might mimic migraines, especially if the patient experiences facial pain or pressure.
• Cervicogenic Headache: Referral of pain from the cervical spine to the head, which can be exacerbated by the postural changes and strain associated with late pregnancy.

Do Not Miss Diagnoses

• Pituitary Apoplexy: A rare but potentially life-threatening condition where a pituitary tumor suddenly hemorrhages or becomes infarcted, leading to severe headache, visual disturbances, and potentially acute hypopituitarism.
• Subarachnoid Hemorrhage: Bleeding into the space surrounding the brain, which can present with a sudden, severe headache (often described as "the worst headache of my life") and is a medical emergency.
• Stroke: Although less common in young pregnant women, stroke can occur and may present with headache among other neurological deficits.
• Venous Sinus Thrombosis: A condition where a blood clot forms in the brain's venous sinuses, which can cause headache, among other symptoms, and is associated with a high risk of complications if not promptly treated.

Rare Diagnoses

• Idiopathic Intracranial Hypertension (IIH): Also known as pseudotumor cerebri, characterized by increased intracranial pressure without a detectable cause, leading to headache and visual disturbances.
• Arteriovenous Malformation (AVM): An abnormal connection between arteries and veins, which can rupture and cause bleeding in the brain, presenting with sudden onset of a severe headache.
• Temporal Arteritis: Inflammation of the blood vessels in the temples, which can cause headache but is less common in younger individuals and more typically seen in those over 50 years old.