What Is Amniotic Fluid and What Are Its Functions?

Amniotic fluid is an essential substance for normal gestation. It's very important to keep up with prenatal check-ups in order to detect any abnormalities.
What Is Amniotic Fluid and What Are Its Functions?

Last update: 14 August, 2021

Amniotic fluid is the substance that surrounds the fetus inside the amniotic sac. This is the sac in which the baby forms and develops until the moment of birth.

Amniotic fluid plays a vital role in development. Most importantly, it protects the baby’s body as well as the mother’s organs. It also helps maintain biological balance.

Because of its important role, amniotic fluid can be used by doctors to obtain information about the health and development of the fetus. Among other things, this allows some diseases to be addressed early.

What is amniotic fluid?

Amniotic fluid is a clear, almost transparent fluid, although with a yellowish tint. It’s normal for it to also have some slight blood spots. It’s usually odorless.

As pregnancy progresses, it may fill with lumps that are flakes of the baby’s skin. After the due date–after 40 weeks–it becomes milky in color. It consists of water, electrolytes, proteins, carbohydrates, lipids, minerals, urea and fetal cells.

The mother begins producing this substance at 12 days of gestation. It then increases progressively until around the 34th week. Then it decreases slightly and the membranes rupture when labor begins, with what’s known as the water breaking.

A fetus in the womb.
The fetus contributes flaked skin cells, which accumulate as the weeks of gestation pass, to the fluid.

What’s its function?

Amniotic fluid plays a key role during gestation. The fetus floats within this substance; if it didn’t exist, development would be impossible.

Although there are still gaps in the science on this subject, we know that the main functions of the amniotic fluid are the following:

  • It facilitates bone growth: The substance allows the fetus to move freely, without the membranes of the amniotic sac sticking to its body. This means it can grow without difficulties.
  • Promotes muscle development: It allows the fetus to move itself into different positions. This contributes to muscle development.
  • Protects the fetus: Amniotic fluid serves as a shock absorber in case of external bumps or sudden movements. It also reduces the impact of uterine contractions.
  • Protects the mother: The fluid also serves as a cushion for the mother against the movements of the fetus. It also prevents damage to nearby organs and prevents compression of the umbilical cord.
  • Creates a favorable environment: By maintaining the proper temperature inside the uterus. It also provides a sterile, i.e. germ-free environment.
  • Allows the exchange of biochemical substances and regulates pH.
  • It promotes lung development: From the second trimester, the fetus inhales and swallows amniotic fluid. This helps its lungs to develop, as well as its gastrointestinal system.
  • Helps movement into the birth canal: The fluid helps the fetus settle into the birth canal. It then lubricates the area to facilitate birth.

Main problems associated with amniotic fluid

The main problems associated with amniotic fluid have to do with volume. The fetus needs a sufficient amount to develop normally. From this point of view, we’ll analyze 3 abnormal situations.

1. Insufficient amniotic fluid

This condition is also known as oligohydramnios and it increases the risk of accidents involving the umbilical cord. The lack of fluid means that the fetus has less room to move freely.

If this situation continues for some time, it’s also possible that lung development will be affected, since the fetus inhales and exhales this substance. Premature labor is also more probable.

The problem may be caused by the mother being dehydrated, changes to the placenta, or premature rupture of membranes. If it’s serious, the doctor will probably decide to bring the delivery forward to avoid greater risks.

2. An excess of amniotic fluid

This case is also known as polyhydramnios. The biggest risk involved is preterm labor, so it requires close medical monitoring. Doctors may treat it with medication or by eliminating the excess. If it occurs late in pregnancy there may be no need for an intensive approach.

Excess amniotic fluid is often caused by gestational diabetes or abnormalities in the fetus. It’s more common in the case of multiple pregnancies.



  • Rincón, D., Foguet, A., Rojas, M., Segarra, E., Sacristán, E., Teixidor, R., & Ortega, A. (2014, September). Tiempo de pinzamiento del cordón umbilical y complicaciones neonatales, un estudio prospectivo. In Anales de Pediatría (Vol. 81, No. 3, pp. 142-148). Elsevier Doyma.
  • Vila BMA, Surí SY, Alfonso ÁB, et al. El desarrollo pulmonar en embriones humanos de ocho semanas: un acercamiento cuantitativo. Medicentro. 2016;20(1):46-55.
  • Madar, H., Brun, S., Coatleven, F., Chabanier, P., Gomer, H., Nithart, A., … & Sentilhes, L. (2016). Fisiología y regulación del líquido amniótico. EMC-Ginecología-Obstetricia, 52(4), 1-10.
  • Faneite, Pedro, et al. “Patologías del líquido amniótico: I: Polihidramnios: incidencia y repercusión perinatal.” Rev. obstet. ginecol. Venezuela (1999): 159-62.
  • Vigil de Gracia, Paulino et al. “Ruptura prematura de membranas.” Guía clínica de la Federación Latino Americana de Sociedades de Ginecología y Obstetricia 2 (2011).
  • Amador de Varona, Caridad Irene, et al. “Oligohidramnios: medidor de salud fetal.” Revista Archivo Médico de Camagüey 17.6 (2013): 121-128.