Why does amniotic fluid embolism occur?

Amniotic fluid embolism usually occurs when women are giving birth. It is a disease with a high mortality rate. Amniotic fluid embolism refers to the entry of amniotic fluid into the human blood during the delivery process of a pregnant woman. The harm of amniotic fluid embolism is very serious. Amniotic fluid embolism can block the blood vessels in the lungs, forming pulmonary embolism and endangering the life of the mother. So why does amniotic fluid embolism occur? The following are the causes of amniotic fluid embolism.

At present, the medical community is still unclear about the cause of amniotic fluid embolism. It may be related to excessive pressure in the amniotic cavity, open blood sinuses, rupture of fetal membranes, etc.:

1. The pressure in the amniotic cavity membrane is too high

After delivery, especially during the second stage of labor, the pressure in the amniotic cavity increases (up to 100-175 mmHg) and significantly exceeds the venous pressure. Therefore, the amniotic fluid may be squeezed into the damaged microvessels and enter the maternal blood circulation.

2. Opening of blood sinuses

Cervical lacerations caused by various reasons during delivery can allow amniotic fluid to enter the maternal blood circulation through damaged blood vessels. When placenta previa, placental abruption, or rupture of the placental marginal sinus occurs, amniotic fluid can also enter the maternal blood circulation through damaged blood vessels or retroplacental sinusoids. During cesarean section or curettage, amniotic fluid can also enter the maternal blood circulation through the blood sinuses at the placenta attachment site, causing amniotic fluid embolism.

3. Rupture of membranes

Most amniotic fluid embolisms occur after rupture of the fetal membranes, and amniotic fluid can enter the maternal blood circulation through damaged small blood vessels in the uterine decidua or cervical canal. During a caesarean section, amniotic fluid can enter the mother's blood circulation through the surgical incision.

In summary, advanced primiparas, multiparas, excessive uterine contractions, premature labor, premature rupture of membranes, placenta previa, uterine rupture, and cesarean section are the predisposing factors of amniotic fluid embolism.

What is amniotic fluid embolism?

Amniotic fluid embolism is a serious complication of labor caused by the sudden entry of amniotic fluid into the maternal blood circulation during delivery, which may lead to acute pulmonary embolism, anaphylactic shock, disseminated intravascular coagulation (DIC), renal failure or sudden death. Amniotic fluid embolism can occur in full-term deliveries and during forceps curettage at 10-14 weeks of pregnancy. Its incidence rate is 1 in 20,000 to 1 in 80,000, and its mortality rate is as high as 80%. It is one of the important causes of maternal mortality.

Embolism is the phenomenon that small solids, liquid droplets or bubbles enter the blood circulation and block blood vessels. The entry of amniotic fluid into the maternal blood circulation is a necessary condition for the occurrence of amniotic fluid embolism. After the amniotic fluid enters the maternal blood circulation, blood tests can reveal tangible substances in the amniotic fluid, such as vellus hair, vernix caseosa, meconium, mucus, keratinized epithelial cells, etc.

Amniotic fluid embolism is very dangerous. First, it may block the blood vessels in the lungs and cause pulmonary embolism. If pulmonary embolism occurs, the body's oxygen supply will be obstructed. What makes amniotic fluid embolism more dangerous than other embolisms such as blood clots is that the components from the fetus in the amniotic fluid are foreign components, which not only block blood vessels but also cause immune reactions and can lead to anaphylactic shock.

Not only that, the blood of pregnant women is in a hypercoagulable state, and the amniotic fluid contains many procoagulant substances. Therefore, disseminated intravascular coagulation (DIC) is likely to occur when the two meet. This will not only produce a large number of microthrombi, but also consume too many coagulation factors at once. The fibrinolytic system is also activated, causing the blood to become unable to coagulate and stop bleeding, causing postpartum hemorrhage or even hemorrhagic shock. When a person is in shock, organ failure may also occur.