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Fluid / cord / growth Call your provider

Oligohydramnios

Also known as Low amniotic fluid, Too little amniotic fluid. Most common in the third trimester and past the due date.

Oligohydramnios is a shortfall of amniotic fluid, less around your baby than there should be. It affects around 4% of pregnancies and grows more common as you approach and pass your due date, when fluid levels naturally drift down. What it means for you turns heavily on when it happens and why. Late in pregnancy it is often handled simply, with closer monitoring and sometimes an early delivery. Earlier in pregnancy it can be more concerning and prompts a search for a cause.

Know the warning signs When to call a provider
How common
About 4%
Of pregnancies; rises to around 12% past the due date, uncommon before term.
When
Third trimester and beyond
Most common late in pregnancy, when fluid naturally declines.
Urgency
Monitored closely
Leaking fluid or reduced fetal movement needs prompt evaluation.
Outlook
Depends on timing
Often manageable near term; more concerning when it starts early.

Understanding it

What is oligohydramnios?

Amniotic fluid does more than cushion. It lets your baby move and build muscle and bone, shields the umbilical cord from being pinched, and fills the developing lungs to help them grow. In the second half of pregnancy, most of it is the baby's urine, in a continuous swallow-and-pass cycle. Oligohydramnios is when the amount falls below normal, diagnosed on ultrasound.

Because the fluid comes mainly from the baby's kidneys later on, low fluid usually points to one of three things: the baby is making less urine, often from reduced placental blood flow; the membranes have ruptured and fluid is leaking; or, less often, a problem with the baby's kidneys or urinary tract. High blood pressure, preeclampsia, diabetes, a growth-restricted baby, going past the due date, and certain medicines (anti-inflammatory painkillers at 20 weeks or later, and some blood pressure drugs) can all contribute.

Timing shapes how worried to be. Low fluid found late, near or past your due date, is common, usually reflects the natural decline, and is managed with closer monitoring and sometimes an earlier delivery. Found early, in the second trimester, it is less common and more concerning, because fluid is vital for lung development then and more often signals an underlying problem.

Most people feel nothing. It surfaces when the uterus measures small, the baby is not growing or moving as expected, or on a routine scan. Two things to report right away: leaking fluid, which can mean ruptured membranes, and your baby moving less. Management ranges from extra hydration and monitoring to planned delivery, depending on how far along you are and the cause.

Symptoms

What are the symptoms?

Oligohydramnios usually causes no symptoms and is found on ultrasound or when the uterus measures small. Two signs are worth reporting promptly: leaking fluid and reduced fetal movement.

Early signs

  • Often none; found on ultrasound or when the belly measures small for dates
  • Leaking fluid from the vagina, which can mean the membranes have ruptured
  • The baby not growing as expected
  • Feeling the baby move less than usual

Emergency signs — call 911

  • Leaking or a gush of fluid from the vagina, which needs prompt evaluation for ruptured membranes
  • Reduced or absent fetal movement
  • Vaginal bleeding
  • Regular contractions or cramping pelvic pain

Why it matters

Risks to you and baby

Umbilical cord compression

Fluid normally keeps the cord floating freely. With too little, it can be pinched, especially during contractions, stressing the baby's heart rate. This is a key reason for close monitoring in labor.

Restricted growth

Low fluid often goes hand in hand with reduced placental blood flow, which can slow the baby's growth. The two are watched together, with growth tracked on serial ultrasounds.

Lung underdevelopment when early

Amniotic fluid is needed for the lungs to grow. When oligohydramnios is severe and starts early, in the second trimester, it can seriously impair lung development, which is the main reason early low fluid is so concerning.

Higher chance of intervention

Oligohydramnios raises the likelihood of induced labor and cesarean birth, both from the monitoring it prompts and because it can reflect a baby not thriving in the womb.

How it's found

How is it diagnosed?

Oligohydramnios is diagnosed on ultrasound by measuring the fluid. Once confirmed, the evaluation looks for a cause, especially ruptured membranes, growth restriction, and, if early, fetal anomalies.

Ultrasound fluid measurement

Ultrasound puts a number on the fluid, either an amniotic fluid index (AFI) or the single deepest pocket. An AFI of 5 centimeters or less, or a deepest pocket under 2 centimeters, defines oligohydramnios.

Checking for ruptured membranes

An exam and tests determine whether the membranes have broken and fluid is leaking, a common and important cause with its own management.

Assessing the baby and placenta

Growth ultrasounds, blood flow (Doppler) studies, and, if found early, a detailed look at the kidneys and urinary tract help identify why the fluid is low.

Most often in the third trimester, at a routine or growth scan, or when the uterus measures small. Followed with repeat scans and fetal monitoring.

Treatment

How is it managed?

Treatment depends on how far along you are and the cause. Near term, monitoring and timely delivery are the mainstays; earlier on, the focus is finding and addressing the cause.

Treatment paths

Before term, the approach is to identify the cause, monitor the baby closely with ultrasounds and non-stress tests, and treat what can be treated, for example stopping a contributing medicine or increasing fluids. Maternal hydration, by mouth or occasionally through an IV, can raise the fluid level, at least temporarily. If the cause is ruptured membranes or reduced placental function, management follows that condition.

Monitoring

Because low fluid can stress the baby, monitoring is stepped up: repeat fluid checks, growth scans, and heart-rate testing.

Can it recur?

Having had oligohydramnios raises the chance of it again, though a specific recurrence rate is not established. Managing any underlying condition, such as high blood pressure, and avoiding contributing medicines lowers the risk next time.

What you can do

Can it be prevented?

  • Avoid contributing medicines

    Do not take anti-inflammatory painkillers (NSAIDs like ibuprofen) at 20 weeks or later unless your provider advises it, and ACE inhibitor blood pressure drugs should be avoided in pregnancy. Both can reduce the baby's urine and the fluid.

  • Stay well hydrated

    Good maternal hydration supports fluid levels and can help, at least temporarily, especially if dehydration is a factor. It is easy and safe to do.

  • Manage underlying conditions

    Keeping high blood pressure and diabetes well controlled supports healthy placental blood flow, which supports the fluid and your baby's growth.

  • Keep your surveillance appointments

    There is no way to prevent oligohydramnios outright, but regular monitoring, especially past your due date, catches it early so it can be managed before it stresses the baby.

Who is more at risk

Risk factors

Going past your due date
Fluid naturally declines near and after term, so being overdue is a leading risk factor.
Low fluid affects about 4% of pregnancies overall but around 12% past the due date.
Reduced placental function
High blood pressure, preeclampsia, and pre-existing diabetes can reduce blood flow through the placenta, lowering the baby's urine output and the fluid.
Ruptured membranes
When the membranes break and fluid leaks out, the amount around the baby drops. This is a common and important cause to identify.
A growth-restricted baby
A baby that is not growing well often has low fluid too, as both can reflect a struggling placenta.
Certain medications
NSAID painkillers taken at 20 weeks or later, and ACE inhibitor blood pressure medicines, can reduce the fluid and should be avoided in pregnancy.

Do not wait

When to call your provider or 911

  • Seek prompt care if you notice fluid leaking or a gush from the vagina, which can mean your membranes have ruptured.
  • Contact your provider right away for reduced or absent fetal movement.
  • Go in for vaginal bleeding, regular contractions, or cramping pelvic pain.
  • Report if your belly seems to be measuring small or your baby feels less active.
  • Ask about monitoring if you are past your due date, when low fluid becomes more common.

Talking to your team

Questions to ask your provider

  • How low is my fluid, and how was it measured?
  • Have you found a cause, such as leaking fluid or reduced placental flow?
  • Is my baby growing well?
  • Given how far along I am, do you recommend delivery or continued monitoring?
  • Are any of my medications contributing, and should I stop them?
  • What signs should make me call or come in right away?

Keep reading

More on oligohydramnios

All pregnancy guides articles

Good to Know

Oligohydramnios FAQs

Common questions about oligohydramnios, answered.

How serious is low amniotic fluid?

It depends heavily on timing and cause. Late in pregnancy, near or past your due date, low fluid is common and often managed with monitoring and timely delivery. Found early, in the second trimester, it is more concerning, because fluid is essential for lung development then and it more often reflects an underlying problem.

What causes it?

Most often the baby is making less urine, usually because blood flow through the placenta is reduced, as in preeclampsia or a growth-restricted baby. Other causes are ruptured membranes, where fluid leaks out, and, less often, a problem with the baby's kidneys. Some medicines, and going past your due date, also contribute.

Can drinking more water help?

It can, at least temporarily. Good hydration, by mouth or sometimes through an IV, has been shown to raise fluid levels, and it is a simple, safe step, especially if you are dehydrated. It is not a cure for every cause, but your provider will often recommend it as part of the plan.

Will I need to deliver early?

Possibly. For isolated low fluid at 36 to 37 weeks or beyond, delivery is often the safest choice. If the fluid drops very low or your baby shows signs of not tolerating the pregnancy, earlier delivery may be advised. Before term, the aim is usually to monitor closely and treat the cause while giving the baby more time.

Does low fluid mean something is wrong with my baby?

Not necessarily, especially late in pregnancy, where it often just reflects the natural decline. When found early or severe, it is more likely to point to an underlying issue, such as reduced placental function or a kidney problem. Late, isolated low fluid with a well-grown, active baby is generally reassuring.

What should I watch for at home?

Two things above all: fluid leaking or gushing from the vagina, which can mean your membranes have ruptured, and your baby moving less than usual. Both warrant a prompt call. Vaginal bleeding, regular contractions, or cramping pain are also reasons to be seen.

Are there medicines I should avoid?

Yes. Anti-inflammatory painkillers like ibuprofen (NSAIDs) should not be taken at 20 weeks or later unless your provider advises it, because they can reduce the baby's urine and the fluid. ACE inhibitor blood pressure medicines should also be avoided in pregnancy. Always check with your provider about what is safe.

Can it be prevented?

There is no reliable way to prevent it outright. What helps is avoiding contributing medicines, staying hydrated, keeping conditions like high blood pressure and diabetes well controlled, and attending your monitoring appointments, especially past your due date, so it is caught and managed early.

Medically Reviewed · Updated

Reviewed by Dr. Grace Lin, MD, FACOG · OB-GYN

Obstetrician-gynecologist focused on reproductive and sexual health for women: pregnancy, BV, yeast, trichomoniasis and HPV/cervical screening. Our editorial guidelines →

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