What is the cause of numbness in the hands of pregnant women while sleeping?

Pregnant women are at high risk of carpal tunnel syndrome, especially in late pregnancy when they gain weight and retain water and sodium, so the pressure in the narrow lumen of the carpal tunnel increases, making them prone to symptoms of carpal tunnel syndrome, numbness, swelling and stiffness in the hands at night or in the morning, pain and weakness in the fingers in severe cases, which may improve with activity, or in severe cases, numbness may persist during the day, in most cases gradually improving after a few weeks of labour, with a few requiring treatment.