What Is Amniotic Fluid?

A fetus in amniotic fluid

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What Is Amniotic Fluid?

Amniotic fluid surrounds the fetus in the womb during pregnancy. It is made up of water, electrolytes, proteins, carbohydrates, lipids, minerals, urea, and fetal cells. The composition is also influenced by the parent's nutrition and their exposure to any toxic substances.

Amniotic fluid is the "water" people refer to when they say their "water broke." The membrane that holds the amniotic fluid is also commonly called the amniotic sac or "bag of waters."

During pregnancy, the fetus is cushioned by amniotic fluid in the womb, and in the past doctors thought that protecting the baby was the fluid's only significant function. However, medical research has now shown that amniotic fluid plays many other roles that are essential for fetal development.

The parent's plasma begins producing amniotic fluid by the 12th day of gestation. By the eighth week, the baby's kidneys begin to make urine. Their urine production is responsible for an increasing percentage of the amniotic fluid as pregnancy progresses.

In the womb, the fetus swallows and inhales the fluid, then passes it out. While this does mean the fetus is swallowing its own urine, this is not as unpleasant as it sounds (because amniotic fluid is actually sterile.)

The fluid volume increases throughout pregnancy until about 34 weeks, when it measures approximately 800 ml (27 ounces). It then decreases slightly until the membranes rupture just before labor begins.

Why Amniotic Fluid Is Important

Amniotic fluid plays critical roles in fetal development, and some have only recently been discovered through medical studies and analysis.

The functions of amniotic fluid include allowing room for the baby to move and develop, cushioning the baby from jostling or impact, filling the lungs during breath-type movements to encourage lung development, protecting against infection, and providing a consistent temperature for the baby.

Because of its primary role in your baby's prenatal growth, amniotic fluid is used as a marker for fetal health and development. The volume can be checked by ultrasound, and your doctor may conduct an amniocentesis to analyze its composition if they suspect any problems with your growing baby.

Analyzing amniotic fluid can give your doctor valuable information about the health of your infant before birth.

This is good news, because certain health issues can be addressed while your baby is still in the womb.

What Color Is Amniotic Fluid?

Amniotic fluid is usually clear to pale yellow in color, although slight streaks of blood are also normal.

Amniotic fluid should be odorless or have a slightly sweet odor. Give your doctor a call if you notice that it smells bad, as this could be a sign of an infection in your uterus.

Amniotic fluid is clearer than urine and not cloudy or thick like vaginal discharge. Also, it typically smells sweeter than other types of discharge.

If you think you are leaking amniotic fluid, call your doctor. Pay attention to the color of the fluid, and be sure to tell your doctor if you notice either of the following:

  • Brown- or green-tinged fluid: may indicate that the baby has passed meconium (its first bowel movement) in the womb. This can cause problems if the baby inhales or swallows it.
  • Red fluid: may indicate problems with the placenta

Common Problems With Amniotic Fluid 

Because amniotic fluid is vital to the well-being of your growing baby, your healthcare team will routinely check it by ultrasound. The volume of fluid must be within a certain range for proper fetal development. The most common issues that arise with amniotic fluid are levels that are too high or too low.

Oligohydramnios (Not Enough Amniotic Fluid)

Oligohydramnios can be caused by late-term pregnancies, dehydration in the parent, placental problems, or ruptured membranes (causing fluid loss). It may also occur if the fetus has kidney problems resulting in decreased urine output and lower production of amniotic fluid.

This condition places fetuses at increased risk of umbilical cord accidents since they do not have as much room to move around unobstructed in the womb.

If oligohydramnios continues long enough, infants may also suffer from impaired lung development, as one of the functions of amniotic fluid is to encourage expansion of the lungs as the baby "breathes" the fluid in and out.

Treatment options depend on the severity of the decreased fluid level, your baby's gestational age, and information about their condition. Labor may need to be induced if your doctor decides it's not safe for the baby to stay in the womb any longer.

This results in a higher number of preterm births among parents with oligohydramnios compared to parents with normal amniotic fluid.

Polyhydramnios (Too Much Amniotic Fluid)

Polyhydramnios can be caused by fetal abnormalities or gestational diabetes. It is also more common in multiple pregnancies (twins or triplets). In some cases, the cause is simply unknown.

Consequences of polyhydramnios include preterm labor, so your doctor will monitor your pregnancy more closely if they detect this condition.

In mild cases occurring late in pregnancy, treatment may not be necessary. In more serious cases, however, the extra fluid may need to be removed or your doctor may recommend medication.

Leaking Amniotic Fluid

As your delivery date approaches, be watching for signs that you are leaking amniotic fluid. If you believe that you are losing fluid (either by a slow leak or a sudden flood), call your doctor. They will determine how much fluid you're losing and how close you are to delivery when deciding on the right course of action.

Rupture of membranes at 37 weeks or later is called premature rupture of membranes (PROM) and may not require treatment. However, your doctor might recommend induction of labor if you have not gone into labor on your own by 24 hours after your water breaks.

Complications can arise for both the mother and the fetus if the amniotic sac breaks too early in pregnancy. When this happens before 37 weeks of gestation, it is called preterm premature rupture of membranes (PPROM).

Infections, smoking, multiple pregnancy, polyhydramnios, cervical surgery, and PPROM in a previous pregnancy all increase a parent's risk of this condition.

Complications from PPROM include infection, impaired fetal development, and early labor and delivery. Typically the goal is to delay labor as long as safely possible for the parent and infant.

This may require hospitalization, bed rest, IV antibiotics, or corticosteroids to speed fetal lung maturity, which can increase the baby's chances of survival if they are born early.

A Word From Verywell

The vast majority of pregnancies progress with no amniotic fluid abnormalities. Even when issues do arise, there are a variety of treatment options to ensure the health and safety of you and your baby.

If you are concerned about the color, smell, or leakage of amniotic fluid during your pregnancy, be sure to check with your doctor or midwife.

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  1. Suliburska J, Kocyłowski R, Komorowicz I, Grzesiak M, Bogdański P, Barałkiewicz D. Concentrations of mineral in amniotic fluid and their relations to selected maternal and fetal parameters. Biol Trace Elem Res. 2016;172:37-45. doi:10.1007/s12011-015-0557-3

  2. Lim ES, Rodriguez C, Holtz LR. Amniotic fluid from healthy term pregnancies does not harbor a detectable microbial community. Microbiome. 2018;6. doi:10.1186/s40168-018-0475-7

  3. U.S. National Library of Medicine, MedlinePlus. Amniotic fluid. Updated April 2, 2021.

  4. Dubil EA, Magann EF. Amniotic fluid as a vital sign for fetal wellbeing. Australas J Ultrasound Med. 2013;16(2):62-70. doi:10.1002/j.2205-0140.2013.tb00167.x

  5. Michigan Medicine, University of Michigan. Rupture of the membranes. Updated October 8, 2020.

  6. U.S. National Library of Medicine, MedlinePlus. Premature rupture of membranes. Updated April 19, 2018.

  7. Dashe JS, Pressman EK, Hibbard JU. SMFM Consult Series #46: evaluation and management of polyhydramnios. Am J Obstet Gynecol. 2018;219(4):B2-B8. doi:10.1016/j.ajog.2018.07.016

  8. U.S. National Library of Medicine, MedlinePlus. Polyhydramnios. Updated April 2, 2021.