What is low amniotic fluid (oligohydramnios)?
Low amniotic fluid is a medical condition in pregnancy in which there is a deficiency of amniotic fluid in the amniotic sac. This can lead to complications for both mother and child, such as fetal malnourishment, cramping and premature labor.
Amniotic fluid helps protect a developing baby and aids fetal muscle, limb, lung and digestive system development. The baby tumbles and moves in the amniotic fluid, and as the pregnancy progresses, the baby takes in and puts out amniotic fluid. The fetus swallows the fluid and "breathes" it into the lungs, then excretes fetal urine and "exhales" the fluid. After the 20th week of pregnancy, amniotic fluid is made up primarily of fetal urine.
In some cases, women may have lower than normal levels of amniotic fluid, which is called oligohydramnios. When the level of amniotic fluid is too low, babies cannot develop properly and may suffer fetal deformation, umbilical cord compression (limiting blood supply with nutrients and oxygen to the fetus) or even death. Low amniotic fluid can be diagnosed at any point in the pregnancy. Doctors routinely check fluid levels at regular checkups; the condition is found with an ultrasound.
Low amniotic fluid is most serious in the first trimester. The baby is vulnerable to malnourishment and developmental problems from a lack of support provided by the fluid. There is also increased risk prior to labor - low fluid levels can pinch the umbilical cord.
What causes low amniotic fluid?
In many cases, doctors do not understand what causes low amniotic fluid. However, there are a few commonly identified causes of oligohydramnios early in pregnancy.
These causes include:
- Certain birth defects in the baby - Problems with the developing fetus's kidneys and urinary tract can cause babies with these birth defects to produce less urine, which is a critical component of amniotic fluid. Also, if the placenta is not providing enough blood and nutrients to the baby, then the baby's growth slows and it may take in and produce less fluid.
- Leaking amniotic fluid - Premature rupture of the membranes (PROM) - tears in the sac that holds the amniotic fluid - and invasive tests such as amniocentesis or chorionic villus sampling (CVS) may cause a woman's amniotic sac to lose fluid. Women with ruptured membranes (i.e., your water breaks) may notice a gush or a slow constant trickle of fluid from the vagina. You may also notice constant wetness in your underwear if your water breaks or if you are leaking fluid after an invasive test. ,
- High blood pressure, which constricts the flow of nutrients to the baby, may cause the baby to stop recycling fluids.
- Diabetes (gestational or type 2) can lead to an imbalance of electrolytes and blood sugar, which leads to dehydration of mother and lack of fluid in the amniotic sac.
- Placenta problems - If you have placenta problems such as placental abruption, the baby's blood supply may be limited, which restricts the baby's growth. If the baby is not developing well, it takes in and puts out less amniotic fluid than expected for its gestational age.
- Lupus can cause kidney problems, which effects amniotic levels
How common is low amniotic fluid?
Oligohydramnios occurs in 8%-11% of pregnancies. It most commonly appears in the last trimester of pregnancy, but it can develop at any time. About one of eight women whose pregnancies continue two weeks past the due date develops oligohydramnios. This happens as amniotic fluid levels naturally decline.
What are the signs or symptoms of low amniotic fluid?
Many women do not know that they have low amniotic fluid because they don't have symptoms. Some women whose membranes have ruptured may notice amniotic fluid rushing or slowly leaking from their vagina. Call your doctor immediately if you think your water may have broken or if you have had an invasive test (such as amniocentesis or chorionic villus sampling) and you notice leaking amniotic fluid.
However, most cases of low amniotic fluid are discovered in a routine ultrasound exam at a regular prenatal appointment. If your doctor diagnoses oligohydramnios, he or she will investigate possible causes and take appropriate action.
What are the treatment options for low amniotic fluid?
Recent studies suggest that women with otherwise normal pregnancies who develop oligohydramnios probably need no treatment. Their babies are likely to be born healthy. Even so, your health care provider may want to watch you closely.
There is no long-term treatment for oligohydramnios, but doctors may recommend one of these short-term solutions:
- Amnioinfusion - If it is warranted, an artificial saline solution may be added to existing amniotic fluid. This procedure is called amnioinfusion. Your doctor may recommend amnioinfusion if he or she cannot detect a suspected fetal problem; additional fluid can help provide better visualization during an ultrasound. Some doctors use amnioinfusion to make it easier to turn a baby that is not in an optimal delivery position (the process of turning a baby is called version).
- Maternal hydration can provide a less invasive alternative to amnioinfusion. When a woman drinks water, the fetus's water levels increase. Hydration can lead to increased placental blood flow volume and fetal urine output
- Fetal membrane sealants can successfully stop leakage from ruptured membranes. However, the safety and overall benefit of sealants is still being researched.
Your doctor will recommend the best course of action depending on your unique situation, but you can minimize the risk of oligohydramnios complications by attending regular prenatal checkups. Your health care provider can monitor the size of your belly and how much amniotic fluid is in your womb. If you have a problem, your physician can take steps to help prevent complications in you and your baby.
Women with high blood pressure, diabetes, lupus and placental problems are at increased risk for oligohydramnios. If you have any of these conditions, be sure to let your health care provider know.
What is the short- or long-term impact of low amniotic fluid?
The risks associated with oligohydramnios often depend on the stage of pregnancy in which it occurs. Amniotic fluid is essential for the development of muscles, limbs, lungs, and the digestive system. The amniotic fluid helps the baby develop muscles and limbs by providing plenty of room to move around. In the first half of pregnancy, too little amniotic fluid can cause the fetus's organs to become compressed, resulting in birth defects of the lungs and limbs. During this period, oligohydramnios increases the risk of miscarriage, preterm birth and stillbirth.
In the second trimester, the baby begins to breathe and swallow the fluid to help their lungs grow and mature. When oligohydramnios occurs in the second half of pregnancy, it can be linked to poor fetal growth. Other complications can include intrauterine growth restriction (IUGR), a condition in which the fetus is smaller than expected for the number of weeks of pregnancy, or preterm birth.
In addition, oligohydramnios can increase the risk of complications during labor, including umbilical cord compression (a situation that can limit the baby's supply of oxygen and nutrients), uteroplacental insufficiency (insufficient blood flow from the placenta to the baby) or inhalation of meconium-stained fluid (feces-contaminated amniotic fluid).
Your doctor will monitor your levels of amniotic fluid throughout pregnancy. If he or she diagnoses oligohydramnios, you and your baby will be treated if appropriate. Causes and severity of the condition differ, and your doctor can work with you to best manage the risks associated with oligohydramnios.
Questions to Ask Your Doctor
- What causes low amniotic fluid during pregnancy?
- How is the level of amniotic fluid measured?
- How accurately can this condition be diagnosed?
- What are the signs or symptoms of low amniotic fluid?
- When am I most likely to get low amniotic fluid? Can the condition improve or change during the pregnancy? When?
- What are the risks to me or my baby as a result of this condition?
- What can I do to prevent or treat low amniotic fluid?
- What are possible complications or side effects of treatments for this condition?
- What should I expect before, during and after treatment?
- Are there activities or daily habits I should change due to this condition?
Our Medical Advisory Board
Wiser Pregnancy's physician advisors review all information on the site to ensure its accuracy, relevance, and consistency with medical best practices.
Michele R. Lauria, MD
Professor of obstetrics and gynecology and attending staff at the Dartmouth University Hitchcock Medical Center in New Hampshire
Linda Burke-Galloway, MD
Senior obstetrics and gynecology physician with the Florida Department of Health and medical malpractice consultant with the U.S. Department of Health and Human Services