Carpal tunnel syndrome is a condition that often occurs in pregnant mothers. It is caused by the involvement of the median nerve in the arm in the carpal tunnel in an inflamed and swollen muscle, causing pain and numbness in the fingers. The pain starts as a tingling pain, often waking up during sleep, and then disappears quickly with movement of the finger. If the condition is severe and prolonged, the hand may also feel inflexible or weak. If left untreated, muscle atrophy of the inner and outer palms of the hand may also occur after several months. Carpal tunnel syndrome usually occurs in both hands and can occur at any time during pregnancy, and is more likely to occur or worsen in the second half of pregnancy, when the pregnant mother begins to retain more and more fluid in her body. Carpal tunnel syndrome usually goes away after the birth of the baby as the swelling subsides. However, this syndrome can continue into the postpartum period if daily life is not taken care of or treated promptly. So which are the culprits of carpal tunnel syndrome in pregnant women? 1, edema Pregnancy edema can increase intertissue fluid by 2.5 liters and plasma fluid by 1.3 liters. Due to systemic edema, tendons, tendon sheaths and connective tissues around nerves are swollen and the median nerve, which is confined in the carpal tunnel, is compressed. The peripheral vessels are dilated during pregnancy and the vascular flow in the hand is 7 times higher than during non-pregnancy. The volume of the carpal tunnel is fixed and there are 9 tendons and the median nerve passing through the carpal tunnel, so when the systemic edema and tissue pressure increase in late pregnancy, it will inevitably affect the carpal tunnel. When the pressure in the carpal tunnel increases, the symptoms and signs of the median nerve distribution area will appear because the volume remains unchanged and the nerve is compressed. 2. Hormones Especially the increase of estrogen, which causes retention edema, plays an important role in the development of this disease. At the end of pregnancy, the concentration of estrogen in the blood reaches its peak. Those who gain more weight during pregnancy are at increased risk of developing carpal tunnel syndrome. Most patients with carpal tunnel syndrome are diagnosed in late pregnancy when symptoms first appear and often involve both hands. At 6 and 9 months postpartum, the remission rate of carpal tunnel syndrome is 89.1% and 95.7%, respectively. 3. Prolactin Prolactin can cause water retention. The blood concentration of prolactin is often elevated at night, which may be the reason why the patient’s pain worsens at night. In addition, relaxin in the body near the time of delivery causes relaxation of the pubic symphysis, etc. It also relaxes the transverse carpal ligament and flattens the carpal arch, causing compression of the median nerve.