What is amniotic fluid made of? Introducing components, roles, and related cases【supervised by doctor】

What is amniotic fluid?

Amniotic fluid is the liquid that fills the uterus during pregnancy. It plays a crucial role in maintaining the environment within the uterus, ensuring optimal conditions for the baby to grow and thrive until birth. In the early stages of pregnancy, amniotic fluid is clear and colorless, but as the pregnancy progresses, it may turn milky due to the baby’s urine production from the kidneys and secretion from the lungs. Additionally, the presence of meconium (fetal stool) in the amniotic fluid can cause it to become cloudy.

The Role of Amniotic Fluid

Amniotic fluid serves the role of protecting the baby from various shocks and stimuli. When the uterus is filled with amniotic fluid, contractions of the uterus help evenly distribute impacts and pressures on the fetus. Additionally, it has a mitigating effect on external temperature changes and maternal conditions, ensuring that the baby maintains a constant body temperature. Amniotic fluid also plays a protective role for the mother by easing pain through its function of preventing direct transmission of fetal movements to the maternal body.

Components and Structure of Amniotic Fluid

The components found in amniotic fluid include various electrolytes, glucose, amino acids, proteins, lipids, urea, uric acid, creatinine, bilirubin, various hormones, growth factors, enzymes, and more. Amniotic fluid contains a diverse range of components necessary for the growth of the baby.

Complications Related to Amniotic Fluid

Amniotic fluid is essential for the healthy development of the baby, but various disorders can lead to complications. Here, we provide detailed explanations of conditions such as polyhydramnios, oligohydramnios, and amniotic fluid embolism.

1.Polyhydramnios

Polyhydramnios is the condition where amniotic fluid is excessively produced. Normally, the amniotic fluid volume gradually increases until around the 34th week of pregnancy and then gradually decreases. The constant regulation of amniotic fluid is maintained as it is produced while the fetus swallows and absorbs it through the gastrointestinal tract. Here, we will introduce the symptoms, causes, and treatment methods of polyhydramnios.

Symptoms

Polyhydramnios often has no symptoms, and some pregnant women may not notice it until diagnosed. However, in severe cases of polyhydramnios, it can lead to difficulties in breathing and early uterine contractions accompanied by pain.

Complications of polyhydramnios include primarily:

• Impending preterm birth due to early uterine contractions
• Premature placental separation after premature rupture of membranes
• Abnormal fetal presentation
• Respiratory difficulties in the mother
• Uterine atony
• Prolapsed umbilical cord
• Postpartum hemorrhage
• Fetal death

Causes

The causes of excessive accumulation of amniotic fluid can be attributed to two main factors: “increased production of amniotic fluid” and “reduced absorption of amniotic fluid.”

Key reasons for the increased production of amniotic fluid include:

• Increased urine production due to maternal diabetes, fetal endocrine disorders, or placental vascular tumors.

Key reasons for the reduced absorption of amniotic fluid include:

• Impaired absorption of amniotic fluid due to congenital abnormalities such as upper digestive tract closure, such as esophageal atresia or duodenal atresia, or functional swallowing disorders.

In addition, leakage of fluid components from the fetus, such as anencephaly, meningomyelocele, or abdominal wall rupture, is also considered a possible cause. More than half of cases of polyhydramnios occur spontaneously and may resolve naturally.

Treatment Methods

In cases where severe pain or early uterine contractions occur, it is necessary to reduce the volume of amniotic fluid. Polyhydramnios can occur spontaneously, resolve naturally, or the cause may remain unknown even after delivery. When polyhydramnios occurs, it is essential to conduct a thorough examination of the fetus, be vigilant for signs of preterm labor, and observe the progression.

In some cases, artificial removal of amniotic fluid may be performed. Currently, there are no strict guidelines regarding the specific volume or rate of amniotic fluid removal, but a method of reducing approximately 1 liter over 20 minutes is often recommended.

2.Amniotic Fluid Embolism

Amniotic fluid embolism is a condition characterized by the blockage of pulmonary capillaries due to the entry of amniotic fluid into the mother’s bloodstream, leading to pulmonary hypertension and associated respiratory circulation disorders. It is typically considered more common in the late stages of pregnancy, but there is also a possibility of occurrence during the 13 to 24 weeks of gestation, particularly in cases of miscarriage. Here, we will introduce the symptoms, causes, and treatment methods of amniotic fluid embolism.

Symptoms

Amniotic fluid embolism generally occurs during or immediately after childbirth. The symptoms mainly include:

• Sudden cardiac arrest
• Sudden difficulty in breathing
• Rapid heartbeat
• Rapid breathing
• Low blood pressure
• Cyanosis
• Hypoxia
• Respiratory failure with intermittent crackles in the lungs

Additionally, as initial symptoms, severe abdominal pain and fetal distress may be observed.

Causes

Factors considered to increase the risk of amniotic fluid embolism include the following symptoms:

• Cesarean section
• Multiple pregnancies
• Maternal aging
• Premature placental separation
• Placenta previa
• Uterine rupture
• Polyhydramnios
• Induced labor
• Forceps delivery
• Abdominal trauma
• Cervical laceration

Not all mothers with these risk factors will necessarily develop the condition. The pathophysiological reasons for why it occurs only in some women are not fully understood, and it is important to recognize that the mentioned risk factors are generally considered possibilities.

Treatment Methods

Supportive therapy is employed to alleviate symptoms in cases of amniotic fluid embolism. This may include transfusions of red blood cells, fresh frozen plasma, and coagulation factors. Ventilatory and circulatory support may be provided, and in some cases, inotropic agents may be necessary. Performing forceps or vacuum delivery promptly after onset may improve maternal outcomes.

3.Oligohydramnios

Oligohydramnios is a condition where the volume of amniotic fluid in the uterus is insufficient compared to the normal amount. The confirmation of amniotic fluid levels is done through ultrasound examinations. To manage amniotic fluid levels, meticulous monitoring and continuous ultrasound assessments are essential. Here, we will introduce the symptoms, causes, and treatment methods of oligohydramnios.

Symptoms

Pregnant women may not experience many noticeable symptoms. The most common sensation is a slight decrease in fetal movements.

Complications of oligohydramnios primarily include:

• Intrauterine growth restriction
• Cesarean section
• Fetal death

Complications that may arise if oligohydramnios occurs from early pregnancy include:

• Limb contractures
• Delayed or incomplete lung maturation

Causes

Factors considered as potential causes of oligohydramnios include:

• Placental insufficiency due to various maternal conditions
• Medications
• Post-term pregnancy
• Fetal kidney disorders causing a decrease in urine production (such as renal agenesis, non-functioning kidneys)
• Intrauterine growth restriction
• Fetal death
• Fetal chromosomal abnormalities
• Rupture of membranes

Treatment Methods

To assess fetal growth, ultrasound examinations are recommended at least every four weeks. In cases of growth restriction, examinations every two weeks are desirable. Amniotic Fluid Index (AFI), which represents the amniotic fluid volume, should be measured at least weekly.

If complications are not present, weekly non-stress tests or fetal monitoring through biophysical profiles, along with delivery around 36 to 37 weeks and 6 days, are recommended.

The relationship between NIPT (Non-Invasive Prenatal Testing) and amniocentesis

Tests such as NIPT (Non-Invasive Prenatal Testing) and amniocentesis are conducted for individuals during pregnancy. Both are essential tests to confirm the health of both the mother and the fetus, but many may not be familiar with the specific differences.

Here, we introduce the roles of NIPT and amniocentesis, serving as a reference for understanding the distinctions.

NIPT (Non-Invasive Prenatal Testing) is a screening test for chromosomal abnormalities

NIPT (Non-Invasive Prenatal Testing) is a prenatal genetic test conducted using the blood collected from the pregnant mother. Since the mother’s blood contains the baby’s DNA, it allows for the screening of fetal chromosomal abnormalities without directly impacting the baby.

NIPT can be performed as early as around the 6th week of pregnancy. However, as it is a screening test, a positive result does not provide a definitive diagnosis. In cases of a positive result, it is recommended to undergo confirmatory testing, such as amniocentesis.

Amniocentesis is a definitive test for chromosomal abnormalities

Amniocentesis is a method for testing chromosomal abnormalities by directly inserting a needle into the pregnant woman’s abdomen to collect amniotic fluid. While it is a highly accurate test, there are associated risks such as infection, bleeding, and amniotic fluid leakage due to the needle insertion into the mother.

Moreover, since amniocentesis requires a sufficient amount of amniotic fluid in the uterus, the test is typically performed around 15-16 weeks of pregnancy. It is known for its high accuracy, nearly approaching 100%. Therefore, if NIPT (Non-Invasive Prenatal Testing) results are positive, undergoing amniocentesis for confirmation is advisable.

At Hiro Clinic, NIPT (Non-Invasive Prenatal Testing) is available for screening chromosomal abnormalities

Amniotic fluid plays a role in protecting both the mother and the baby from shocks and pressure. Troubles related to amniotic fluid include conditions like polyhydramnios, amniotic fluid embolism, and oligohydramnios. Additionally, the relationship and details of NIPT (Non-Invasive Prenatal Testing) and amniocentesis were explained.

At Hiro Clinic, NIPT testing is available, and in the case of a positive result, we can refer you to a partnering testing company for amniocentesis. Since NIPT is a screening test, if a positive result occurs, it is recommended to undergo the confirmatory test, amniocentesis. As NIPT can be performed earlier in pregnancy, having this screening first and subsequently opting for amniocentesis provides reassurance.

Article Editorial Supervisor

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Dr Hiroshi Oka

NIPT specialist clinic, MD

Graduated from Keio University, School of Medicine