The hardening and tightening of the stomach in the middle of the night during late pregnancy may be caused by false contractions, clinical signs, placental abruption and other reasons. 1. False contractions: In late pregnancy, when the fetus moves more in the uterine cavity, it may stimulate the uterine wall, which may cause the stomach to be tight and hard in the middle of the night, but there is usually no pain, which belongs to false contractions. 2. Clinical signs: If the stomach becomes hard and tight in the middle of the night during late pregnancy, accompanied by redness, pain and regular contractions, it may be a sign of labor. 3. Placental abruption: Placental abruption refers to the partial or total detachment of the placenta from the uterine wall before the delivery of the fetus in its normal position, which is a serious complication during pregnancy and may be manifested as a hard and tight stomach in the middle of the night during late pregnancy. Pregnant women who feel that their stomachs are hard and tight and have no relief from rest should go to the obstetrics department of a regular hospital in time, and be given targeted treatment under the guidance of a professional doctor.