Causes of polyhydramnios in late pregnancy

Excessive amniotic fluid in late pregnancy is a very unfavorable situation and has great harm. It is generally difficult to give birth naturally in this situation, and the possibility of natural birth will become lower. There are many reasons for excessive amniotic fluid, which are related to fetal malformations and pregnancy complications. In addition, if there are chromosomal abnormalities or twins, it may lead to excessive amniotic fluid. Let's take a look at this aspect.

Causes of polyhydramnios in late pregnancy

The cause of about 1/3 of polyhydramnios is unknown, but most severe polyhydramnios may be related to fetal malformations and pregnancy complications.

1. Fetal malformation: Among pregnant women with polyhydramnios, 18%-40% have fetal malformation. Neural tube defects are the most common, accounting for about 50%, of which open neural tube defects are the main ones. When the baby is anencephaly or has spina bifida, the meninges are exposed, the choroidal tissue proliferates, the exudation increases, and central swallowing disorders and antidiuretic hormone deficiency occur, which lead to excessive amniotic fluid formation and reduced reflux. Fetal esophageal and duodenal atresia can cause difficulty in the fetus swallowing amniotic fluid, causing polyhydramnios.

2. Chromosomal abnormalities: Trisomy 18, trisomy 21, and trisomy 13 fetuses may have difficulty swallowing amniotic fluid, causing polyhydramnios.

3. Twin pregnancy: About 12% of twin pregnancies are complicated by polyhydramnios, which is more than 10 times that of single pregnancy. In the case of monozygotic, monochorionic and diamniotic sacs, the two placentas have arteriovenous anastomosis, which can easily lead to twin-twin transfusion syndrome. The recipient fetus's circulating blood volume increases, the fetal urine volume increases, and polyhydramnios occurs.

4. Pregnancy complicated by diabetes: The mother's high blood sugar level leads to increased blood sugar in the fetus, producing osmotic diuresis, and increased placental and fetal membrane exudation leading to polyhydramnios.

5. Fetal edema: Polyhydramnios is related to fetal immune edema (such as hemolysis due to maternal-fetal blood type incompatibility) and non-immune edema (mostly caused by intrauterine infection).

6. Placental and umbilical cord lesions: Giant placenta and velamentous attachment of the umbilical cord can lead to polyhydramnios. When the diameter of placental chorioangioma is greater than 1 cm, 15%-30% may be accompanied by polyhydramnios.

7. Idiopathic polyhydramnios: accounts for about 30%, without abnormalities of the pregnant woman, fetus or placenta. Unknown cause

Symptoms of polyhydramnios

1. Chronic polyhydramnios: more common. It usually occurs between 28 and 32 weeks of gestation. The specific manifestations are that the amniotic fluid slowly increases over several weeks, with mild compression symptoms or no symptoms. Most pregnant women can gradually adapt, and they only feel that their abdomen is growing faster. Examination showed that the uterus was under tension, the uterine height and abdominal circumference were greater than those of the same pregnancy, there was an obvious sensation of fluid tremor, the fetal position was clear or unclear, and the fetal heart rate was distant or unclear.

2. Acute polyhydramnios: less common. The disease usually occurs during the 20th to 24th week of pregnancy, with a sudden increase in amniotic fluid and a significant enlargement of the uterus within a few days. The patient feels abdominal pain, back pain, difficulty in movement, tight and shiny skin, and difficulty breathing and even cyanosis due to the elevated diaphragm, and cannot lie flat. Examination may reveal a highly distended abdomen, tense and thin skin, dilated inferior epigastric veins, and varicose veins and edema of the vulva; the uterus is larger than the gestational month and tense, the fetus cannot be examined clearly, and the fetal heartbeat is distant or unclear.