Suddenly less amniotic fluid at 40 weeks of pregnancy can be dealt with by vaginal trial of labor, cesarean section to terminate the pregnancy, the specific need to comply with medical advice. If the amniotic fluid suddenly becomes less than 40 weeks pregnant, you should go to the hospital in time for checkups. If the mother’s physical condition is good, cervical ripeness is good, there are no serious cardiopulmonary diseases, hyperemesis gravidarum, pre-eclampsia and other complications, fetal heartbeat response is good, fetal reserve function is still good, and there is no obvious intrauterine hypoxia, then it is feasible to go to the delivery of the fetus by trial of labor in a vaginal way. If the amniotic fluid suddenly becomes less at 40 weeks of pregnancy, accompanied by gestational hypertension syndrome, gestational diabetes mellitus, heart disease, insufficient cervical ripeness, obvious intrauterine hypoxia, fetal malposition, etc., it is necessary to terminate the pregnancy by Caesarean section as soon as possible. Sudden decrease of amniotic fluid at 40 weeks of pregnancy may be caused by aging of the placenta, premature rupture of membranes, and serious pregnancy complications.