When the amount of amniotic fluid is <300ml, it is called oligohydramnios, which is a traditional concept, but it is difficult to accurately estimate the total amount of amniotic fluid in both vaginal delivery and cesarean section. In recent years, due to the application of imaging, especially the application of obstetric ultrasound, the diagnosis of oligohydramnios has become more accurate, and the diagnostic criteria have been unified, and has been gradually used in clinical practice.The criteria for diagnosis of oligohydramnios by ultrasound are amniotic fluid index (AFI) <5cm or maximum depth of amniotic fluid pool <2cm.Symptoms and SignsPregnant women often feel pain due to fetal movement, abdominal circumference and height of the uterine fundus are smaller than the month of gestation, and the activity of the fetus is limited. Fetal activity is limited and natural reversal is not easy, so breech presentation is common. The duration of pregnancy is prolonged, often exceeding the expected date of delivery by 2 to 3 weeks. Primary contraction weakness or uncoordinated contraction often occurs during labor, and the mouth of the uterus is dilated slowly, which makes it easy for the first stage of labor to be prolonged. Amniotic fluid is very small, sticky and yellowish-green, resulting in fetal hypoxia. The lack of amniotic fluid causes various developmental abnormalities. If the amniotic fluid occurs in early pregnancy, part of the fetal body surface can be adhered to the amniotic membrane, or the formation of amniotic bands so that the fingers or limbs are severed. If amniotic fluid is low in late pregnancy, the fetus will have dry skin like parchment. Because of low amniotic fluid, the fetus is in a mandatory position in the uterus, which is easy to be compressed and cause special musculoskeletal deformities, such as hand and foot deformities, dorsal curvature, slanting neck, and bending of upper and lower limbs. There is also often fetal lung hypoplasia, which may be caused by: ① developmental defects within the lungs cannot excrete the fluid that maintains the amniotic fluid volume; ② due to low amniotic fluid, the uterus compresses the fetal chest, which affects the chest wall and lung expansion; ③ lack of fluid inhalation into the terminal alveoli, which hinders lung development. In normal pregnancy, the inhalation of appropriate amniotic fluid volume is important for fetal lung expansion and development. Amniotic fluid in early and middle gestation is often terminated by abortion due to fetal anomalies. Pathogenesis 1, fetal malformations Many congenital malformations, especially urinary malformations, are associated with amniotic fluid insufficiency, such as congenital renal agenesis, renal hypoplasia, polycystic kidneys and urethral stenosis or atresia, etc. The above malformations lead to the production of urine. The above malformations lead to the decrease or inability to produce urine, the urine produced can not be discharged or discharged less, no urine or less urine, resulting in the decline of amniotic fluid production, normal absorption of amniotic fluid, and finally, the occurrence of amniotic fluid is too small. 2, placental insufficiency The placenta is the organ of material exchange between the fetus and the mother, and a decrease in placental function can lead to a decrease in fetal blood volume, a decrease in the blood supply to the fetal kidneys, and finally a decrease in fetal urine production. Placental function is determined by the placental blood supply, the maternal barrier of the placenta, and the effective working area of the placenta.Decreased placental function usually includes a decrease in placental blood supply, a decrease in placental maternal barrier permeability, and a decrease in the effective area of the placenta. Decrease in placental blood supply theoretically includes decrease in blood volume of pregnant women, decrease in blood pressure of pregnant women, and abnormalities in the supply vessels of the placenta, etc. However, at present, it is believed that the decrease in blood volume of pregnant women is the main reason for the decrease in placental blood supply. 3, the role of drugs Many drugs can cause amniotic fluid, common non-steroidal antipyretic analgesics and angiotensin converting enzyme inhibitors, non-steroidal antipyretic analgesics in the most researched is indomethacin. Examination methods 1, ultrasound is the main method of diagnosing amniotic fluid, including qualitative diagnosis and semi-quantitative diagnosis. ultrasound found that the amount of amniotic fluid is obviously reduced, amniotic fluid and fetal interface is unclear, fetal limbs are obviously gathered and overlapped, that is, the qualitative diagnosis of amniotic fluid can be made. After qualitative diagnosis, the depth of the amniotic fluid pool is measured to make a semi-quantitative diagnosis of amniotic fluid insufficiency. During 28-40 weeks of gestation, the maximum amniotic fluid pool diameter measured by B-mode ultrasound is stable in the range of 5,1cm±2,0cm; if the maximum amniotic fluid pool vertical depth (AFV) is ≤2cm, it is considered to be oligohydramnios, and if it is ≤1cm, it is considered to be severe oligohydramnios. Currently, the amniotic fluid index (AFI) method is used to diagnose amniotic fluid, which is more accurate and reliable than AFV. AFI ≤ 8cm is the critical value for diagnosing amniotic fluid, and if AFI ≤ 5cm, it is diagnosed as amniotic fluid hypospadias. 2.Magnetic resonance technology is a new imaging technology developed in recent years which can be applied in obstetrics. In addition to accurately determining the depth of the amniotic fluid pool, magnetic resonance technology can also estimate the total amount of amniotic fluid by using three-dimensional imaging technology and volume calculation technology, which is an important method of diagnosing amniotic fluid hyponatremia. For patients with oligohydramnios, while it is important to determine the amount of amniotic fluid through imaging techniques, a greater role of imaging techniques is the diagnosis of fetal malformations, and clarifying the presence or absence of fetal malformations is the key to formulating a treatment plan. Ultrasound has been a milestone in the intrauterine diagnosis of fetal malformations, and the emerging magnetic resonance technology has even greater advantages over ultrasound. Prognosis of amniocentesis and its effects on the mother and child: Early-onset amniocentesis refers to the occurrence of amniocentesis in the middle of pregnancy and before the middle of pregnancy, which is relatively rare, and the common causes are fetal malformations and fetal growth restriction, with a very poor outcome of the pregnancy. Common causes of late-onset oligohydramnios are overdue pregnancy, premature rupture of membranes, fetal growth restriction, fetal distress, maternal hypovolemia, maternal use of indomethacin for fetal preservation and use of captopril (Kapton) to treat hypertensive syndromes of pregnancy, among other conditions. Fetal malformations usually occur during pregnancy with low amniotic fluid, which refers to fetal malformations secondary to low amniotic fluid, known as tetralogy of amniotic fluid. As a result of low amniotic fluid, the uterus tightly wraps around the fetus, resulting in restricted fetal growth and movement, which in turn leads to abnormal organ growth and function, and ultimately to the classic condition of oligohydramnios tetralogy of Fallot. Tetralogy of Fallot includes pulmonary hypoplasia, peculiar facial features, limb deformities and growth retardation. During labor and delivery, low amniotic fluid usually results in uncoordinated contractions, slow cervical dilatation, and fetal distress from umbilical cord compression, so the cesarean section rate increases, and even if the baby is delivered vaginally, the vaginal delivery is relatively difficult and prone to birth injuries. After birth, the fetus is prone to neonatal asphyxia and other neonatal diseases, and the neonatal mortality rate increases significantly. Preventive measures Women of childbearing age should strengthen the eugenics publicity and guidance, do a good job of prenatal screening, 3 months pregnant card regular systematic health checks; after 37 weeks of pregnancy to 40 weeks of pregnancy before the planned delivery to reduce the incidence of low amniotic fluid. Can affect the amount of amniotic fluid of the drug at present there are mainly anti-inflammatory pain, can reduce the amount of amniotic fluid used to treat excessive amniotic fluid with attention to the detection of the amount of amniotic fluid in time to reduce the amount of or stop the drug, to avoid the cause of amniotic fluid is not suitable for use in the 34th week of pregnancy, because it can cause premature closure of the fetal ductus arteriosus. 1, from the 37th week of pregnancy, often do ultrasound, such as found that the amniotic fluid is too small can be appropriate early admission. Oxygen therapy can be performed twice a day for 3 minutes each time during the waiting period for labor, and listen to the fetal heart sounds diligently and pay attention to the changes in the fetal heart. Teach the pregnant women to monitor themselves, pay attention to the changes of fetal movement, and perform left lateral position more often. At the same time, the amount of water can be increased appropriately to improve the circulating blood volume and relatively increase the amniotic fluid volume. Repeat the fetal heart monitoring every 1~3 days, or repeat the ultrasound examination, in order to facilitate timely grasp of the intrauterine fetal situation. 3.During labor and delivery, we should listen to the fetal heartbeat diligently, and use the fetal heartbeat monitor to monitor continuously, report to the doctor at any time when there is any situation, and inhale oxygen first, and inject 40ml of 5% glucose with vitamin C1g. If the situation does not improve, especially when the membranes are broken with amniotic fluid turbid, the labor should be terminated as soon as possible, and those who cannot deliver in a short time should have a cesarean section in a timely manner. 4.Delivery should be ready for all the rescue items, when there is amniotic fluid fecal infection, timely clean up the mouth, nose, throat secretions, suction out mucus and amniotic fluid containing fetal feces. 5.After delivery, dry the baby in time, pay attention to keep warm, observe the newborn's general condition, report any abnormality to the doctor in time and deal with it accordingly. Treatment with medication 1. If amniotic fluid is found to be too small during pregnancy, the pregnancy should be terminated immediately if there is a clear combination of fetal abnormality. 2.Diagnosis of amniotic fluid during pregnancy If it is clear that there is no fetal abnormality and the fetus is already mature, termination of pregnancy can be considered, and the way of termination of pregnancy can be considered cesarean section. 3.Amniocentesis Decrease in amniotic fluid volume is the main reason why amniotic fluid adversely affects the mother and child during pregnancy and delivery, and increasing amniotic fluid volume through amniocentesis is a targeted treatment measure.