Many women report that their headaches are worse with their periods. However a true menstrual migraine is a headache that occurs only in association with the menstrual cycle. This may turn out to be an artificial distinction. Fluctuations in estrogen levels remain one of the most consistent triggers for migraine. For this reason, migraineurs often do better when they are on constant hormone replacement. Often, women with regular cycles and predictable headaches will "pulse prophylax" by taking a preventative medication only during the time during which they are at risk for the headache.