What Does Low Amniotic Fluid Mean During Pregnancy?
While low amniotic fluid during pregnancy, or oligohydramnios, may seem worrisome, the condition is usually treatable. Learn about symptoms, causes, diagnosis, and more.
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Medically reviewed by Lulu Zhao, M.D.
Low amniotic fluid, or oligohydramnios, is a condition that involves too little amniotic fluid around the fetus. Being diagnosed with oligohydramnios, or having symptoms of it like decreased fetal movement, will likely raise some concerns. You're probably wondering what this means for you and your unborn baby, how the condition is treated, and whether it will affect your delivery in any way.
The good news is oligohydramnios doesn't usually cause complications, and infants generally have favorable outcomes. We reached out to OB-GYNs to help us understand everything about low amniotic fluid levels, including symptoms, causes, treatment, and more.
What Is Oligohydramnios?
Oligohydramnios is characterized by low amniotic fluid, which is the liquid surrounding your unborn baby in the womb. It's also the liquid that releases when your water breaks during labor.
Why is oligohydramniosis cause for concern? Too-low levels might prevent amniotic fluid from fulfilling its purposes, which include:
Protecting the fetus from infections
Cushioning the fetus from external pressures and blows
Helping your unborn baby's respiratory and digestive system develop
Regulating body temperature of the fetus
Preventing umbilical cord compression
Note that the amount of amniotic fluid in the womb changes over time. It increases steadily as your baby grows, reaching a peak volume at about 34 to 36 weeks gestation. At that point, it starts to level off, slowly decreasing as delivery approaches. As such, the amount of amniotic fluid you have toward the end of pregnancy is naturally in the lower range of normal.
Related: Is Having Too Much Amniotic Fluid a Cause for Concern?
What Causes Low Amniotic Fluid or Oligohydramnios?
In early pregnancy, low amniotic fluid is usually related to a health problem in the pregnant parent or the fetus. This includes fetal kidney abnormalities, placental problems, certain medications, and fetal growth restriction, says Adi Davidov, MD, associate chair and director of obstetrics and gynecology at Staten Island University Hospital.
Toward the end of pregnancy, when low amniotic fluid is more common, the decreased levels may be related to a pregnant person's water breaking early. A pregnancy that's past term could also cause low amniotic fluid levels, explains Dr. Davidov.
Whatever the cause of low amniotic fluid, it should be taken seriously. "Basically, if noted, this requires additional work up, close monitoring, and possibly delivery," says Priyanka Venkataraman, MD, board-certified OB-GYN.
How Common Is Oligohydramnios?
Low amniotic fluid impacts about 4.4% of pregnancies, though it's less common in preterm pregnancies, impacting only 1% of these. Oligohydramnios is also more likely in post-term pregnancies (after 42 weeks), as amniotic fluid levels naturally decrease after your due date.
This is comparable to what Dr. Venkataraman sees in her practice. "I have noticed this in two to three out of 20 pregnancies, usually in the third trimester," she shares. "It's very rarely noted earlier in the pregnancy, in which case it could mean a structural abnormality with the fetus," she adds.
Related: Worried About Your Water Breaking? Here's What to Know
Symptoms of Low Amniotic Fluid
One symptom of low amniotic fluid is decreased fetal movement, says Dr. Davidov. "The parent may feel their unborn baby move less than usual," he says.
Dr. Venkataraman agrees that decreased fetal movement is a possible symptom of oligohydramnios, and it's usually the first sign that's noticed. "When there is less fluid, it restricts the space the fetus can move in," she explains.
Another possible sign of low amniotic fluid is that your uterus will measure smaller than expected according to how far along you are, says Dr. Venkataraman. You might also leak fluid from the vagina.
However, it's important to note that, in some cases, expectant parents don't experience any clear symptoms. This means that you could have low amniotic fluid without realizing it.
Related: Do Babies Poop and Fart in the Womb?
Oligohydramnios Symptoms
If you have signs of oligohydramnios, or low amniotic fluid, they may include the following:
Decreased fetal movement
Uterus measuring small for your baby's gestational age
Leaking fluids from the vagina
Not gaining enough weight during pregnancy
How Is Low Amniotic Fluid Diagnosed?
Of course, symptoms like decreased fetal movement don't always indicate that you have low amniotic fluid. To find this out for sure, your health care provider will need to do some diagnostic testing.
According to the American College of Obstetricians and Gynecologists (ACOG), the only test that measures amniotic fluid is an ultrasound (including biophysical profiles, an ultrasound-based test). While non-stress tests can suggest low fluid by the presence of what's called variable decelerations, they don't actually measure amniotic fluid.
Ultrasounds are used to diagnose low amniotic fluid by "either measuring the greatest vertical pocket of amniotic fluid or calculating an amniotic fluid index," describes Dr. Davidov. In other words, ultrasounds are able to assess and quantify the amount of amniotic fluid surrounding the fetus.
In high-risk pregnancies, you're usually getting serial growth scans by ultrasound, and that's when low fluid is commonly found. Biophysical profiles can then be done in between these every 3- to 4-week growth scans if something pathological is found (low fluid, low growth, etc). Dr. Venkataraman says that "if an abnormal result is noted, it may require additional testing, closer monitoring, or even delivery depending on how far along the pregnancy is."
Related: Top 13 Pregnancy Fears (and Why You Shouldn't Worry)
Treatment for Low Amniotic Fluid
Treatment for low amniotic fluid will depend on the cause, as well as how far along you are in your pregnancy. "In most cases, when the patient is close to their due date, we deliver the baby," says Dr. Davidov. "In instances earlier in the pregnancy, we monitor the unborn child's health and deliver if there are any worrisome findings."
However, there are no specific ways to increase amniotic fluid, adds Dr. Venkataraman. "This is most likely an indicator of stress to the pregnancy, requiring additional work up, monitoring, intervention for the underlying stressor, including possibility of delivery," she describes.
Some research indicates that drinking extra fluids can increase amniotic fluid—especially during the third trimester—but it's unclear how much this may help. Your provider might also encourage rest.
Complications of Low Amniotic Fluid
Having too little amniotic fluid can lead to complications, especially in the first two trimesters. These can include:
Birth defects
Miscarriage
Stillbirth
Infection
Third trimester oligohydramnios may lead to slow growth, umbilical cord compression, and a higher chance of labor problems or C-section delivery.
When to Contact Your Health Care Provider
The good news is that low amniotic fluid is a relatively rare diagnosis, and it usually happens during the third trimester when your unborn baby can be safely delivered. If you think you might be dealing with a case of low amniotic fluid, you should contact your health care provider.
Importantly, one of the main signs of low amniotic fluid—decreased fetal movement—is something you should take seriously regardless of the cause. Contact your health care provider right away if you notice less movement.
Related: 3 Questions About Labor You've Been Too Embarrassed to Ask
You should also contact your provider immediately if you develop a fever above 100.4°F, have sudden and intense cramping or contractions, experience a severe headache, have blurred vision, or experience any type of fluid leaking from your vagina.
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