Where does amniotic fluid come from? Amniotic fluid is not ordinary water, it is essential for the normal growth and development of the fetus. After the middle of pregnancy, the main source of amniotic fluid is the fetus’ urine, and another secondary source is the fluid secreted by the fetal lungs. In late gestation, the fetus can produce more than 1000mL of urine per day, so this much amniotic fluid must have an outlet, otherwise it will lead to excess amniotic fluid. The main way of amniotic fluid absorption is swallowed by the fetus, to put it bluntly, “how to urinate out, how to drink down”, can not urinate and defecate anywhere is reasonable, right? If the fetus “poops” in the womb, it has to be swallowed together with the urine. But don’t get too hung up, fetal urine and meconium are relatively clean, and amniotic fluid has an anti-bacterial effect. Another secondary absorption route for amniotic fluid is the blood vessels on the surface of the placenta. Amniotic fluid provides a space for the fetus to move around, which is important for the development of the fetus’ musculoskeletal system; it is also important for the fetus to be able to swallow amniotic fluid properly for the development of its gastrointestinal tract. Amniotic fluid also provides a constant temperature to protect the fetus from direct pressure from the uterus, as well as to protect the fetus from injury when the mother’s abdomen is impacted. The amniotic fluid has another special antibacterial function, which reduces the chance of intrauterine infection in the fetus. The amount of amniotic fluid cannot be directly measured clinically. The common method of determining the amount of amniotic fluid is ultrasonography. The most common causes are fetal anomalies, twins and diabetes. The most common fetal anomalies associated with hyperhydramnios include central nervous system anomalies (e.g. anencephaly) and digestive tract anomalies (e.g. esophageal atresia, duodenal atresia). In the presence of excessive amniotic fluid, the most important thing to look for is the cause, including further detailed fetal structure examination by an ultrasonographer, MRI if necessary, and fetal chromosome examination. Even after a thorough and detailed examination, there are still about 70% of cases of excessive amniotic fluid for which no definite cause can be found. Serious complications of excessive amniotic fluid include premature rupture of membranes, preterm labor, placental abruption, and postpartum hemorrhage due to weak contractions. In the absence of other maternal and fetal indications, amniotic fluid overload does not require intervention in most cases. If the amount of amniotic fluid increases significantly in a short period of time, causing severe discomfort and respiratory distress to the mother, amniocentesis may be considered to release the amniotic fluid. For most mothers-to-be with excessive amniotic fluid, there is no need to be overly concerned because the prognosis for babies with unexplained excessive amniotic fluid, mild amniotic fluid, and excessive amniotic fluid without detectable fetal abnormalities is mostly better. Hypohydramnios If a single maximum amniotic fluid volume is used as the standard, ≤2 cm is considered as hypohydramnios; if the Amniotic Fluid Index AFI is used, ≤5 is considered as hypohydramnios. The prevalence of amniotic fluid is 1-2%, and the most common causes are fetal malformations (mainly abnormal kidney development) and reduced fetal urine output due to placental dysplasia (often accompanied by fetal growth and developmental delay). The incidence of adverse perinatal fetal prognosis associated with hypohydramnios is higher than that of hyperhydramnios, including fetal malformations, preterm delivery, stillbirth, and fetal lung dysplasia. In terms of management, the main focus is to find the cause, strengthen monitoring, and terminate the pregnancy if necessary. Some foreign medical institutions will do amniotic fluid perfusion to prolong the gestational week and reduce complications, while less is done in China.