Headache in the fourth month of pregnancy may be related to poor rest, emotional changes, cold, fever, hormonal fluctuations in the body and pregnancy complications: 1. Poor rest: if a pregnant woman does not rest well and does not get enough sleep, her brain will be in a state of fatigue and she is prone to plant nerve dysfunction, thus inducing headache. Generally, the headache will be relieved naturally after sufficient rest. 2. Emotional changes: when you are emotionally excited or too nervous, it is easy to induce cerebral vascular spasm, increase cerebral blood flow and headache. In this case, first of all, we should pay attention to adjusting emotions and relaxing, and we can help relieve the headache with cold compresses or hot compresses; 3. Cold: some pregnant women are prone to headache after blowing wind and getting cold. This is because the cold air stimulates vasoconstriction, blood flow when the pressure is high, blood flow is slow, there may be a lack of blood supply to the brain, thus appearing headache. In this case, attention should be paid to good warmth measures to reduce the onset of headache; 4. Cold and fever: After cold and fever, many harmful metabolites such as lactic acid, carbon dioxide and potassium ions will be produced inside the body, which will stimulate the nervous system and thus induce headache. At this time, we should pay attention to more rest and actively treat the cold; 5. Hormonal fluctuations in the body: the rise of estrogen in the body of pregnant women may cause headache, which is normal and will recover on its own without treatment; 6. Pregnancy complications: for example, pregnancy combined with anemia and pregnancy combined with hypertension may cause headache, when pregnant women are anemic, the whole body is in a state of ischemia and hypoxia, the nervous system ischemia and hypoxia will manifest as headache. When a pregnant woman is anemic, the whole body is in a state of ischemia and hypoxia, and the nervous system is deprived of blood and oxygen. When the blood pressure rises, it may induce cerebral vascular spasm, resulting in increased intracranial pressure and thus headache. In this case, the first thing to do is to actively treat the original disease, correct the anemia and control the blood pressure.