What Is Amniotic Fluid? Its Composition And Functions

what is amniotic fluid made of and why is it important

A tiny baby floating in a liquidy womb – and featuring prominently in this mesmerizing image is the amniotic fluid! What role does amniotic fluid play in your pregnancy? Does it affect the baby’s development? We’ll answer these questions and more here.

The amniotic fluid and sac maintain a slightly higher temperature (around 99.7 °F) than the mother to keep the environment cozy and comfortable.1


The light yellow amniotic fluid is a complex substance that surrounds the growing fetus during pregnancy. The amniotic fluid and the growing fetus are both contained in an amniotic sac. This sac is the baby’s safe zone and provides the baby enough room to swim, tumble around, and build muscle tone.2

Composition Of Amniotic Fluid

Fun Fact! Amniotic fluid and the amniotic sac are not unique to human beings or even mammals. Birds and reptiles also lay eggs that have amniotic sacs and fluid within them. As higher animals evolved from reptiles, the pattern of giving birth shifted from laying eggs to producing live offspring, and the system within evolved to produce what can be considered a modified egg, amniotic fluid, umbilical cord, and the placenta.3


Amniotic fluid is essentially a mixture of many things – ions, biological compounds, fetal excretions, and salts. Miraculously, amniotic fluid is swallowed and inhaled by the fetus, and then excreted through the developing digestive and urinary systems. The composition of amniotic fluid changes as pregnancy progresses.4

It contains hormones that stimulate cell differentiation, embryonic development, tissue regeneration, and regulation of the immune system. As pregnancy progresses, the placenta takes on the primary nutritive role, and the amniotic fluid supplements this with additional proteins.5


Amniotic Fluid: Changes Over The Weeks

First 8 Weeks

Amniotic fluid begins to form almost as soon as the embryo implants itself in the uterus wall. Approximately in the first 8 weeks of pregnancy, the volume of amniotic fluid increases faster than the size of the embryo. The water in the amniotic fluid initially passes from the mother’s blood through the fetal membranes to the fetus. With the development of the placenta and the fetal organs, water and solute from the mother’s blood flow through the placenta to the fetus and then to the amniotic fluid. Here’s something to marvel at – the fetal skin has not yet developed a thickened outer layer of skin filled with the protein keratin (or become waterproof in simple terms). So, the fluid passes through the skin both ways. This is why the composition of fetal blood and amniotic fluid is similar. Keratinization of the skin takes place only around weeks 19–25 of pregnancy.

Levels of amniotic fluid fluctuate throughout pregnancy. In the early stages of pregnancy, the volume of amniotic fluid increases from about 25 ml at 10 weeks to about 400 ml at 20 weeks. At about 34 weeks into gestation, the fluid content is the highest at 800 ml. After this, the content begins to fall steadily to 600 ml by the time the baby is ready to be born.6


Week 8 Onward

The fetus begins swallowing the amniotic fluid soon after 8–10 weeks of pregnancy. The quantity swallowed though is not large enough to make a difference in the volume of amniotic fluid at that stage. As the pregnancy progresses, amniotic fluid from around week 20 is largely composed of fetal urine, skin cells shed by the baby, and secretion of fluids from its nose, mouth, lungs, and throat. As the baby breathes, lung fluid leaves the baby in tiny quantities with each breath. Although small, this makes a significant contribution to amniotic fluid volume. Swallowing and transfer across membranes take care of fluid removal. This cycle of addition and removal of amniotic fluid ensures a stable and healthy balance of fluid in the amniotic sac.7

Main Functions Of Amniotic Fluid

Provides Mechanical Protection: One of the main functions of amniotic fluid is to prevent mechanical trauma to the fetus. It keeps the growing fetus encased safely, acting as a shock absorber of sorts. Amniotic fluid provides a well-lubricated environment for the fetus to move around in, thereby helping in bone growth and strengthening.8


Amniotic fluid performs a host of vital functions in pregnancy – it nourishes the growing fetus, helps with growth, and provides antimicrobial and mechanical protection. Besides providing the perfect, sheltered environment for the tiny fetus, amniotic fluid also drives the functioning of sensitive systems that come together in fetal development.

Allows Development of Body Parts: Amniotic fluid circulates freely within the womb, keeping every part of the body lubricated. That allows for the growth of the external body parts such as fingers and toes and stops them from becoming clumped together. It also helps in the development of the lungs and the digestive system.9


Offers A Natural Immune System: Amniotic fluid is a significant player in the baby’s natural immune system. Many of the antimicrobial substances that make up the natural immune system of the baby can be found in amniotic fluid. These antimicrobials protect the baby from various bacteria, fungi, protozoa, and viruses.10

Delivers Nutrition: Amniotic fluid is a perfectly balanced nutrition system that provides the growing fetus with everything it needs. It is rich in carbohydrates, electrolytes, enzymes, hormones, lipids, lactate, proteins and peptides, and pyruvate. Taurine, an important constituent of bile, is found in higher quantities in amniotic fluid when compared to maternal serum. Amniotic fluid thus constitutes a nutrition supplementing mechanism that helps the fetus grow fully.11


Provides A Diagnostic Medium: Amniotic fluid also helps doctors to assess fetal health. Since the 1970s, amniocentesis, a medical procedure that draws amniotic fluid for testing, has been a valuable tool for detecting chromosomal abnormalities, neural tube defects, genetic diseases, and several other inborn problems in blood health and metabolism. 12

Imbalance In Amniotic Fluid Levels

The level of amniotic fluid is closely regulated both by the mother’s body and also by fluid exchange with the fetus in the womb. In the majority of pregnancies, this complex regulating process works flawlessly. There are rare occasions, however, when the level of amniotic fluid can go awry, becoming too high or low. This situation will need medical intervention.


In this condition, there is too little amniotic fluid in the sac. Only 4 percent of pregnant women are likely to develop this condition. Dehydration, late pregnancies, high blood pressure or diabetes in the mother, ruptured membranes around the fetus, development issues with the baby’s kidney or urinary tract, or problems with the placenta can all cause this condition.

Risks Of Oligohydramnios

  • Oligohydramnios can be a serious problem when it is diagnosed in the first half of pregnancy. In this stage, birth defects because of compression of fetal organs or even a miscarriage are quite possible.
  • If detected in the second half of pregnancy, oligohydramnios can cause the baby’s growth rate to be less than average, cause a premature delivery or a cesarean delivery, or labor problems such as meconium in the fluid, or umbilical cord compression.
  • It is most commonly diagnosed in the third trimester when the mother is past her due date by around two weeks.13

When You Should See Your Doctor

Oligohydramnios is not a condition that a pregnant woman can detect herself. It can be detected only during an ultrasound exam.

What Next?

Reassuringly, medical science offers several options to treat this condition. The choice of treatment will depend on the cause of the problem and the stage at which it is detected. Before delivery, oral rehydration fluids can help increase amniotic fluid levels. On other occasions, amniotic fluid may be infused into the womb during labor to improve the chances of a normal delivery. These decisions will be made by your doctor who will be closely monitoring the baby’s progress.

If you are not full term yet, your amniotic fluid levels and you will be monitored closely. Your baby’s activity is likely to be monitored through non-stress and contraction stress tests.14


This condition when amniotic fluid levels are too high is even rarer and is seen only in about 1 percent of pregnancies. Also called amniotic fluid disorder, it can occur if the mother has uncontrolled diabetes or if the baby swallows and absorbs less than normal amounts of amniotic fluid. Problems in the baby’s developing body systems may also be a reason for polyhydramnios. In certain cases, no reason can be detected. Whatever the cause, there is no way to prevent polyhydramnios.15

Risks Of Polyhydramnios

You will be relieved to know that most women diagnosed with polyhydramnios won’t have any problems and will go on to have a healthy baby. Occasionally, complications can set it in, including premature birth (before 37 weeks) or problems in the baby’s position before delivery or the placement of the umbilical cord.16

When You Should See Your Doctor

Polyhydramnios is a gradual condition and you may have no noticeable symptoms at all. It is usually detected during an ultrasound exam during the later stages of pregnancy. However, you should contact your doctor if

  • You think your belly is growing big very fast.
  • If you experience breathlessness, constipation, heartburn, or swollen feet. But then again, all of these symptoms are common to pregnancy, so it is rather difficult to pinpoint when exactly you should consult your doctor.17

What Next?

If you are diagnosed with polyhydramnios, you would probably have to see your doctor and go through ultrasound scans more frequently over the rest of your pregnancy. The doctor will try to find out why you have the condition and treat you accordingly.

  • A mild case of polyhydramnios is resolved by keeping the mother under observation to record changes in fluid level.
  • Severe cases may require amniocentesis to remove excess fluid.
  • Medication may be given that will stop more amniotic fluid being produced.
  • You might be advised plenty of rest.18

Ayurveda’s View On Amniotic Fluid

In Ayurveda, it is understood that all disorders of the body are metabolic in nature. Disorders of the abdomen are often considered to be due to a lack of digestive capacity. Ayurveda believes that the accumulation of fluid is an indication of kapha. Hence, treatments for polyhydramnios must focus on removing excess fluid systemically. Treatment involves the use of specific medicines administered with alkaline carriers and cow urine.19

Chinese Medicine May Treat Oligohydramnios

A traditional Chinese herbal medicine extracted from Salvia miltiorrhiza (red sage) may be able to treat oligohydramnios. In one study of 43 pregnant women, salvia was administered intravenously and the women were monitored for any improvement in blood circulation and better functioning of the placenta. The results showed a success rate of about 70% with no side effects. 20

Can Swallowing Amniotic Fluid Be Dangerous?

During birth, the baby, who has been “breathing” liquid while inside the womb progresses toward breathing in air. At this time, she may inhale some amniotic fluid containing meconium – a baby’s first stools passed into the fluid before or during labor. This could enter the lungs and is called meconium aspiration (“swallowing” the amniotic fluid is the common, layman’s terminology for this condition).

These meconium particles can obstruct tiny airways. The baby’s lungs are not yet developed fully to be able to exchange gases. So, doctors may use artificial resuscitation to take care of this. Alternatively, they may resort to amnioinfusion – diluting the thick meconium with sterile fluid that is transported through a tube inserted into the mother’s uterus. Many such complications are managed on call by neonatologists during delivery.21