Amniotic fluid and pregnancy: everything you need to know

Liquide amniotique et grossesse : tout ce qu’il faut savoir

Amniotic fluid is a sterile substance in which the baby bathes throughout pregnancy. It is essential to the development and growth of the embryo, and later the fetus. This precious fluid not only protects it from temperature variations, external shocks and infections, but also enables it to move and develop its lungs and muscles. But what is amniotic fluid? What role does it play? And what to do if the quantity is too low or too high? Here's everything you need to know.

What is amniotic fluid?

Amniotic fluid is the biological fluid surrounding the fetus in the uterine cavity. It is contained in the amniotic sac, also known as the "sac of waters", which is made up of two membranes: the amnion and the chorion.

Throughout pregnancyThroughout pregnancy, this fluid, 97% of which is water, enables the baby to develop normally, while being protected from external aggressions (blows, sudden movements, noises, temperature changes, bacteria, etc.).

How is amniotic fluid formed during pregnancy?

Amniotic fluid appears rapidly after fertilization, during the creation of the amniotic sac, which begins around the 7th day of pregnancy.

During the first few weeks, most amniotic fluid is produced by the embryo as a result of extracellular expansion. It is then secreted by transudation through the membranes and epidermis of the fetus until the 4th month of gestation. Between 20 and 25 weeks of amenorrhea (SA), the baby's skin becomes keratinized and no longer allows water to pass through. This fluid is then formed from urine, pulmonary secretions and cells from the amniotic cavity. The fetus constantly swallows and expels it, contributing to its circulation and renewal.

The composition of amniotic fluid remains fairly complex. It consists mainly of water and electrolytes (99%), but also contains minerals (calcium, sodium, potassium, trace elements, etc.), amino acids and fetal epithelial cells.

What role does this fluid play during pregnancy?

Amniotic fluid plays a vital role during pregnancy. It is essential to the healthy development of the fetus, and is a valuable indicator of the baby's health.

From fetus to baby

To help the fetus develop into a baby, amniotic fluid maintains an ideal temperature of 37.5 degrees, while protecting it from external shocks. This fluid also enables the fetus to make active movements in the womb, thus stimulating its motor skills.

By swallowing and expectorating it, the fetus develops its lungs while absorbing the water and nutrients it needs. It also experiences flavour, a sensation produced by the smell and taste of food consumed by pregnant women during pregnancy.

Finally, the antibacterial properties of amniotic fluid protect the child from most infections, with the exception of toxoplasmosis and cytomegalovirus (CMV). cytomegalovirus (CMV) which can cross the placental barrier.

An indication of fetal health

The quantity of amniotic fluid is a valuable indicator of fetal well-being. By means of an ultrasound scan, a gynecologist or midwife can determine whether the volume is normal, insufficient (oligohydramnios) or too great (hydramnios). Two methods can be used to do this:

  • Chamberlain's method, involving the large vertical cistern (LVC);
  • the Phelan method, which uses an amniotic index (ILA).

Large vertical cistern (LVC)

Chamberlain's assessment is an ultrasound examination designed to explore the entire amniotic sac in order to calculate the depth of the largest vertical cistern (LVC). A diagnosis can be made from the measurement obtained:

  • a value of less than 2 cm may indicate oligohydramnios;
  • a value between 2 and 8 cm indicates a normal volume;
  • a value greater than 8 cm suggests hydramnios.

Amniotic index (ILA)

The Phelan method is based on evaluation of the amniotic index (ILA). During this examination, the sonographer virtually divides the uterus into four parts (quadrants) intersecting at the umbilicus. He then measures and adds up the depth (vertical diameter) of the fluid cisterns identified:

  • if less than 5 cm, there's a risk of oligohydramnios;
  • if between 5 and 18 cm, the amount of fluid is normal;
  • if it's over 18 cm, the pregnant woman may be suffering from hydramnios.

How much amniotic fluid is in the uterine cavity?

The amount of amniotic fluid in the uterine cavity varies throughout pregnancy. However, it can sometimes be too little (oligohydramnios) or too much (hydramnios). Find out more!

Normal amniotic fluid volume

As the weeks go by, amniotic fluid adapts to the weight and development of the fetus, following a precise cycle:

  • Before 20 weeks' amenorrhea, its volume increases progressively in the uterine cavity (from 20 ml to around 200 ml between 7 and 16 SA).
  • It then stabilizes at around 980 ml between 20 and 34 SA.
  • Finally, from 34 SA onwards, the quantity of amniotic fluid decreases, reaching around 800 ml at term.

However, this quantity varies from one pregnant woman to another. It is generally between 250 ml and 2 liters for a normal pregnancy.

Insufficient fluid: oligohydramnios

Oligohydramnios refers to an insufficiency of amniotic fluid. This is the most common anomaly, affecting between 0.4% and 4% of pregnancies. Pregnant women suffering from oligohydramnios have an amniotic fluid volume of less than 200 ml. Oligohydramnios can be caused by a fissure in the water sac, or by a placental, maternal or fetal anomaly.

Oligohydramnios can occur at any stage of gestation, and can lead to complications of varying severity, depending on the child's stage of development: pulmonary hypoplasia, musculoskeletal anomalies, and so on. For this reason, it must be promptly treated and monitored by a doctor or gynecologist. Treatment obviously depends on the cause and degree of severity.

If you're suffering from temporary oligohydramnios, you'll need to rest and probably be confined to bed. If, on the other hand, the oligohydramnios is early and occurs before the 5th month, due torupture of the amniotic sac, the medical profession will be obliged to propose termination of the pregnancy. After the 5th month, however, antibiotic treatment may be prescribed. Finally, if the rupture occurs at the end of the pregnancy or shortly afterwards, delivery will be induced.

Too much: hydramnios

Hydramnios or polyhydramnios refers to an excess of amniotic fluid in the uterine cavity (more than 2 liters). This anomaly has a variety of causes: gestational diabetes, preeclampsia and infection in the mother-to-be, or anemia and congenital malformations in the fetus.

Two types of hydramnios have been identified by doctors:

  1. Chronic hydramnios (which develops slowly around the 3rd trimester of pregnancy and remains fairly controllable);
  2. Acute hydramnios (which appears abruptly as early as the 2nd trimester of pregnancy and leads to a variety of symptoms that are difficult to tolerate: contractions, uterine pain, respiratory discomfort, etc.).

Like oligohydramnios, it carries many risks: premature delivery, rupture of the water sac, procidence of the cord, developmental abnormalities, and so on. Hydramnios therefore requires rapid treatment, which varies from case to case. For example, medical treatment may be recommended to reduce the baby's urine output. Sometimes, punctures are also necessary to prevent premature birth.

How can I control the amount of fluid in a pregnant woman's pouch?

The amount of amniotic fluid in a pregnant woman's pouch can be checked by clinical examination or ultrasound. In the first case, the doctor or gynaecologist may suspect that the volume is too large or too small, if the mother-to-be 's uterus is too large or too small for the stage of pregnancy.

In the second case, the sonographer observes on screen the distribution of the liquid around the baby and measures the cisterns thus formed. An amniotic index is then obtained to determine whether the quantity is normal, too low or too high.

What is the usual color of amniotic fluid?

The color of amniotic fluid should be clear. This means it is still sterile and free of bacteria. Amniotic fluid can, however, take on other hues.

A greenish or cloudy appearance is generally due to the emission of meconium (the baby's first stool), revealing that the fetus is suffering. The medical profession can then induce delivery.

A red color often indicates the presence of a retroplacental hematoma, requiring an emergency Caesarean section.

What are the problems associated with fetal fluid?

Problems related to amniotic fluid include infections of the fluid, membranes and placenta (intra-amniotic infection), as well as partial loss of fluid as the pregnancy nears term.

Fetal infection

Intra-amniotic infection occurs when bacteria from the vagina enter the uterine cavity and contaminate the fluid, amniotic sac or placenta. These germs can cause serious harm to the child and severe complications for the mother.

Once the water has broken, creating a sterile environment for the fetus, bacteria can more easily enter the uterus. The risk of infection therefore increases with duration. Gynaecologists and doctors therefore do their utmost to ensure that delivery takes place within 24 hours of rupture of the membranes.

Partial fluid loss

In some cases, the membranes making up the amniotic cavity rupture in part, and the fluid drips out continuously. This is most often seen towards the end of pregnancy, but can occur well before term.

Partial loss of amniotic fluid can increase the risk of fetal infection. So, if in doubt, go to the maternity hospital. If fissuring is confirmed, it will be treated according to the stage of pregnancy. Before 22 weeks' amenorrhea, the volume of the liquid will be measured, and antibiotics and an infectious work-up will be prescribed. Between 22 and 35 weeks' gestation, the pregnant woman will be hospitalized and cared for until delivery.

Why amniotic fluid testing?

Amniocentesis is a medical examination in which a small quantity of amniotic fluid (between 10 and 20 ml) is taken. It is performed by a doctor during an ultrasound scan. A very fine needle connected to a syringe is gently inserted into the womb of the mother-to-be.

The test is performed to detect chromosomal abnormalities (such as trisomy 21), toidentify genetic diseases (such as cystic fibrosis) and to diagnose parasitic (toxoplasmosis) or viral (cytomegalovirus) infections.

Amniocentesis is not compulsory, but is recommended for women over 38 or with a Down's syndrome child. It may also be prescribed when the prenatal screening blood test for trisomy 21 proves positive.

A relatively rare procedure,amnioscopy is performed at the end of pregnancy, when the term has passed. A lighted tube is inserted into the cervix to check the appearance and color of the fluid passing through the amniotic sac.

When does the amniotic fluid drain from the uterine cavity?

Amniotic fluid is evacuated from the uterine cavity at the moment of rupture of the water sac, also known as "water breaking". The two membranes (amnion and chorion) rupture, releasing the fluid.

When it occurs around term, it indicates that the baby is ready to be born and that delivery is imminent. Labour usually begins a few hours later.

If the amniotic sac ruptures prematurely (before 22 weeks of amenorrhea), the pregnant woman is placed under close surveillance in hospital, where she undergoes a number of tests and treatments to delay delivery as long as possible.

Amniotic fluid FAQs

How does the amniotic fluid test work?

The amniotic fluid test is performed during an ultrasound scan. The pregnant woman lies on her back, and the doctor places the probe on her belly to calculate the volume of fluid, which will appear in black on the screen. He will use either the Phelan method (using the amniotic index) or the Chamberlain method (measuring the large vertical cistern).

Can the baby swallow amniotic fluid?

Yes, and this is completely normal! From the 4th month of gestation, the baby even swallows large quantities to irrigate its pulmonary system and keep its kidneys working. Some of the amniotic fluid ingested is filtered, then transformed into urine.

Does drinking lots of water increase fluid intake?

To date, no scientific study has succeeded in proving beyond doubt that a pregnant woman's state of hydration can influence the quantity of amniotic fluid. Drinking plenty of water does not increase the volume of amniotic fluid. Good maternal hydration does, however, help limit the risk of urinary tract infections, a source of bacteria that can contaminate this sterile substance.

Does a pregnant woman's food pass into the amniotic fluid?

Yes, the nutrients from a pregnant woman's food pass through the membranes, giving the amniotic fluid its taste and smell. Your baby will absorb the flavors of the foods you eat during pregnancy.

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The information contained in the articles on is general information only. Although reviewed by health professionals, this information is not error-free, does not constitute health advice or consultation, and is not intended to provide a diagnosis or suggest a course of treatment. Under no circumstances may this information be used as a substitute for medical advice or consultation with a healthcare professional. If you have any questions, please consult your doctor.