Common Disorders of the Amniotic Fluid

Pregnant woman getting ultrasound scan in doctor's office
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Of all the miracles of the human body, amniotic fluid deserves a special place. Essential for fetal growth, development, and safety prior to birth, amniotic fluid is made from the parent's plasma beginning about the twelfth day after conception.

By the eighth week of gestation, the baby's kidneys begin to make urine. Amniotic fluid is composed of less parental plasma and more fetal urine until birth.

For the fluid to properly serve all its functions, there must be a certain volume present throughout gestation. Either too much or too little amniotic fluid will cause problems for the baby's growth and development.

Ultrasound is commonly used to determine the amniotic fluid volume by one of two measurements: amniotic fluid index (AFI) or single deepest pocket (SDP), also known as maximum vertical pocket (MVP). Studies have shown conflicting results about which method is more accurate for diagnosing adverse pregnancy outcomes.

One review summarized the research in this area by stating that while neither method is superior, AFI tends to overestimate amniotic fluid abnormalities. The authors recommend the use of SDP a second check when problems are suspected.

However, a 2015 study of 950 pregnancies found that both measurements were highly correlated with the actual amount of amniotic fluid. Research is ongoing in this area, and many doctors use both methods for a clear picture of the amniotic fluid volume.

There are three categories of amniotic fluid volume:

  1. Oligohydramnios: Less than 200 mL of amniotic fluid at term
  2. Adequate fluid: AFI between 5 and 25 cm
  3. Polyhydramnios: 2000 mL of fluid or greater

Oligohydramnios

When a person has too little amniotic fluid, they are diagnosed with oligohydramnios. This is defined as having less than 200 ml of amniotic fluid at term or an AFI of less than 5 cm.

It is clinically very hard to prove prior to delivery. After the birth, examining the placenta for the presence of amnion nodosum can detect oligohydramnios.

Depending on when a person is diagnosed, there are different complications to look for. Keep in mind that the majority of people with this conditions will not have problems with their pregnancy, especially if it occurs in the last two trimesters.

Oligohydramnios in early pregnancy generally has a poor prognosis, especially when pulmonary hypoplasia (poor fetal lung development) or fetal limb deformities are present. Amniotic adhesions can also cause deformities or constriction of the umbilical cord.

Even with oligohydramnios, ultrasound resolution and screening for anomalies is very adequate. So ultrasound is still an effective way to screen for deformities both associated and non-associated with oligohydramnios.

Later in pregnancy, oligohydramnios is one of the signs of fetal distress. This occurrence can cause compression of the cord, which can lead to fetal hypoxia, meaning that the baby is not getting enough oxygen.

Meconium, if passed, cannot be diluted in cases of true oligohydramnios. A 2017 meta-analysis of over 35,000 pregnancies found that babies born to mothers with oligohydramnios had a higher incidence of meconium aspiration syndrome, c-section delivery, and NICU admission.

Other concerns with oligohydramnios include:

Diabetes is commonly thought of as a reason for oligohydramnios, but it does not have to cause a problem with the pregnancy with proper treatment.

What treatment options are available for people with oligohydramnios? Replacing the fluid through amnioinfusion (adding saline solution through the cervix) is sometimes used to improve conditions for the baby until delivery.

Induction is not always the best option when oligohydramnios is present. There are many factors that need to be taken into consideration.

In the absence of IUGR and fetal anomalies, women diagnosed with oligohydramnios can have an appropriately sized baby with no health problems.

Polyhydramnios

Polyhydramnios, or too much fluid, is defined as more than 2000 ml of fluid at birth or an AFI of more than 24 cm. This condition occurs in approximately 1% of pregnancies.

When the fetus cannot swallow amniotic fluid in normal amounts, it may accumulate in the uterus and reach abnormally high levels. This often happens in babies with gastrointestinal problems or neural tube defects.

Polyhydramnios can also occur when too much fluid is produced. In about 50 percent of cases, however, the cause is unknown.

Polyhydramnios can be caused by a wide range of maternal and fetal conditions, but it is most commonly seen with the following issues:

There are varying degrees of polyhydramnios; some doctors classify it as mild, moderate, or severe. While the degree of polyhydramnios does not appear to influence the baby's weight, it can carry the risk of complications, including:

  • Fetal malpresentation (a baby not presenting head-first at delivery)
  • Postpartum hemorrhage
  • Premature rupture of membranes (PROM)
  • Preterm labor
  • Umbilical cord prolapse

Treatment options vary, depending on the cause and severity of each case. In mild cases, treatment may not even be necessary.

Controlling any underlying conditions (such as gestational diabetes) can help reduce the amount of extra fluid. Your doctor may also suggest medication and/or selective use of amniocentesis to reduce the fluid volume.

A Word From Verywell

Considering that the current testing is not beneficial in all aspects of prediction, we need to address how to find a manner that is non-invasive to treat these disorders of amniotic fluid. So the question becomes how often do we test, who do we test, and what do we do with the results? Right now, the answers are not clear and should be taken on a case by case basis.

The majority of women diagnosed with either of these problems, will not give birth to a baby with a problem, but the concern is there and does need to be appropriately addressed by her care provider.

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9 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Lim ES, Rodriguez C, Holtz LR. Amniotic fluid from healthy term pregnancies does not harbor a detectable microbial communityMicrobiome. 2018;6. doi:10.1186/s40168-018-0475-7

  2. Coombe-Patterson J. Amniotic fluid assessment: amniotic fluid index versus maximum vertical pocket. J Diag Med Sonography. 2017;33(4):280-283. doi:10.1177/8756479316687269

  3. Magann EF, Ounpraseuth S, Chauhan SP, et al. Correlation of ultrasound estimated with dye-determined or directly measured amniotic fluid volume revisited. Gynecol Obstet Invest. 2015;79(1):46-49. doi:10.1159/000365088

  4. Stanek J. (2019) Amniochorial Membrane Nodules. In: Khong T, Mooney E, Nikkels P, et al. (eds) Pathology of the Placenta. Springer, Cham. doi:10.1007/978-3-319-97214-5_38

  5. March of Dimes. Oligohydramnios. Updated June 2013.

  6. Children's Minnesota. Oligohydramnios treatment at Midwest Fetal Care Center.

  7. Rabie N, Magann E, Steelman S, Ounpraseuth S. Oligohydramnios in complicated and uncomplicated pregnancy: a systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2017;49(4):442-449. doi:10.1002/uog.15929

  8. March of Dimes. Polyhydramnios. Updated June 2013.

  9. U.S. National Library of Medicine. Polyhydramnios. Updated May 17, 2019.

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