What are the causes and symptoms of excessive amniotic fluid?

Amniotic fluid is a watery liquid that can provide a constant temperature environment for the fetus. When the amount of amniotic fluid exceeds the normal amount, this condition is clinically called polyhydramnios. People should also have an understanding of the causes and manifestations of polyhydramnios. Excessive amniotic fluid cannot be ruled out as the cause of fetal malformation.

1. Among pregnant women with polyhydramnios, about 20% to 50% have fetal malformations, among which central nervous system and upper gastrointestinal tract malformations are the most common. In fetuses with anencephaly, encephalocele and spina bifida, the meninges are exposed, the choroidal tissue proliferates, and the exudate increases, leading to polyhydramnios.

2. The incidence of polyhydramnios in multiple pregnancies is 10 times that of single pregnancies, especially in monozygotic twins, and often occurs when one of the fetuses is heavier. This is because the blood circulation between the monozygotic twins is mutually communicated, and the dominant fetus has more circulating blood and increased urine volume, resulting in polyhydramnios.

3. Various diseases of pregnant women and fetuses, such as diabetes, ABO or Rh blood type incompatibility, severe fetal edema, pregnancy-induced hypertension, acute hepatitis, and severe anemia in pregnant women. The blood sugar level of the fetus of a diabetic pregnant woman will also increase, causing polyuria and being discharged into the amniotic fluid. When the blood types of mother and fetus are incompatible, the placenta is heavier. It has been reported that when the placenta weight exceeds 800g, 40% of them are combined with polyhydramnios, and the pathological basis is chorionic edema affecting fluid exchange.

4. Acute polyhydramnios: It mostly occurs during the 20th to 24th week of pregnancy. Due to the sharp increase in amniotic fluid, the uterus rapidly enlarges within a few days, similar to the size of a full-term pregnancy or a twin pregnancy. In a short period of time, the uterus is extremely enlarged, the diaphragm rises, and breathing difficulties occur. The pregnant woman cannot lie flat, and may even develop cyanosis. The pregnant woman looks painful, has excessive abdominal tension, feels painful, and has a reduced appetite, resulting in constipation. The enlarged uterus compresses the inferior vena cava, affecting venous return, causing edema and varicose veins in the lower limbs and vulva. Pregnant women have difficulty walking and can only lie on their side.

5. Chronic polyhydramnios: It accounts for about 98% and mostly occurs between 28 and 32 weeks of pregnancy. The amniotic fluid can gradually increase within a few weeks. It is a moderate and slow increase. Most pregnant women can adapt to it. During prenatal examinations, it is often found that the uterine height and abdominal circumference are greater than those of pregnant women of the same period. During physical examination, pregnant women with excessive amniotic fluid are found to have a swollen abdomen that is larger than the gestational month. The pregnancy chart shows that the uterine height curve exceeds the normal percentile. The skin of the abdominal wall is shiny and thin. When palpated, the skin feels tense and there is a sense of fluid vibration. The fetal position is unclear, and sometimes the fetal part can be felt to float or sink. The fetal heartbeat is distant or inaudible. Pregnant women with excessive amniotic fluid are prone to complications such as pregnancy-induced hypertension, abnormal fetal position, and premature birth.