The causes of diminishing amniotic fluid vary between early, mid and late pregnancy because the source of amniotic fluid is different. In early and middle pregnancy, amniotic fluid is getting less and less, often combined with fetal malformation, while in late pregnancy, the main consideration is placental hypoplasia. The specific reasons are as follows: 1, fetal malformations: abnormal fetal kidney development, Potter syndrome, chromosomal structure abnormalities, such as trisomy 18, trisomy 21, etc., can lead to low amniotic fluid in early and middle pregnancy, it is recommended to carry out prenatal diagnosis to clarify the cause; 2, placental hypofunction: acute placental hypofunction can lead to low amniotic fluid in pregnant women, so it is recommended to check when pregnant women have acute low amniotic fluid Placental function, through fetal heart monitoring, ultrasound to understand the amniotic fluid situation. In conclusion, it is recommended that mid- to late-stage patients consider early termination of pregnancy when the fetus is mature