What causes headaches in early pregnancy?

Pregnancy-related headaches during the first trimester are a common and usually benign symptom, often attributed to significant hormonal fluctuations—particularly rising levels of estrogen and progesterone—which can affect cerebral blood flow and vascular tone. Additionally, physiological adaptations such as increased blood volume (beginning as early as week 5–6), changes in blood pressure, heightened sensitivity to stress or fatigue, and alterations in sleep patterns or caffeine intake may contribute. Dehydration, low blood sugar from nausea or irregular eating, and tension-type headaches related to musculoskeletal adjustments (e.g., posture changes or neck strain) are also frequent contributors. While most early-pregnancy headaches are primary (e.g., migraine or tension-type) and not indicative of serious pathology, clinicians must remain vigilant for red-flag features—including sudden-onset severe headache (“thunderclap” pain), headache with fever, visual disturbances, focal neurologic deficits, or worsening with lying flat—as these may signal secondary causes such as preeclampsia (though rare in the first trimester), intracranial hemorrhage, or venous sinus thrombosis. Evaluation should include a thorough history, blood pressure measurement, and neurological examination; imaging is reserved for cases with atypical features or clinical concern. Conservative management—adequate hydration, regular meals, sleep hygiene, stress reduction, and nonpharmacologic therapies like thermal therapy or acupuncture—is typically first-line. Acetaminophen remains the preferred analgesic when medication is necessary, used at the lowest effective dose and shortest duration possible.