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Fluid / cord / growth Call your provider

Polyhydramnios

Also known as Too much amniotic fluid, Excess amniotic fluid. Second half of pregnancy, often found in the third trimester.

Polyhydramnios is a buildup of too much amniotic fluid, the water your baby floats in. It is uncommon, affecting about 1% to 2% of pregnancies, and in more than half of cases the fluid is only mildly increased with no cause ever found. When mild, it often needs nothing more than monitoring and frequently settles on its own. When more pronounced, your provider looks for a reason, such as diabetes or something with the baby, and watches more closely, because extra fluid can bring complications.

Know the warning signs When to call a provider
How common
About 1% to 2%
Of pregnancies; most cases are mild and have no identified cause.
When
Second half of pregnancy
Builds gradually, often found on a third-trimester ultrasound.
Urgency
Monitored closely
Mild cases just watched; sudden belly swelling or preterm labor signs need prompt care.
Outlook
Usually good
Mild polyhydramnios often resolves; outcomes depend on any underlying cause.

Understanding it

What is polyhydramnios?

Amniotic fluid is the water your baby floats in. It cushions the baby, lets it move and practice breathing and swallowing, and helps the lungs and gut develop. The amount is normally balanced: the baby swallows fluid and passes it as urine, in a continuous cycle. In polyhydramnios that balance tips toward too much, and it is diagnosed on ultrasound.

In more than half of cases the extra fluid is mild and no cause is found; these idiopathic cases usually do well and often resolve on their own. When a cause turns up, the most common is maternal diabetes, where higher blood sugar leads the baby to make more urine. Other causes involve the baby: harder swallowing from a digestive-tract blockage, an infection, fetal anemia, or, in identical twins sharing a placenta, twin-to-twin transfusion syndrome.

Most people with mild polyhydramnios feel nothing. With a lot of extra fluid, the stretched uterus can bring shortness of breath, belly discomfort or tightness, leg swelling, and a sense of the belly growing fast. That same stretch raises the chance of preterm labor, early water breaking, the baby settling in an awkward position, and heavier bleeding after birth.

Management turns on how much fluid there is and why. Mild cases are usually just monitored. When symptomatic or severe, options include a medicine that reduces the baby's urine output (used only before 32 weeks) and, occasionally, draining some fluid. Your provider also treats any underlying cause and plans delivery timing. For most people, especially with a mild increase, the outlook is reassuring.

Symptoms

What are the symptoms?

Mild polyhydramnios usually causes no symptoms and is found on ultrasound. A more significant buildup stretches the uterus and can bring noticeable discomfort.

Early signs

  • Often none, especially when mild
  • Shortness of breath, from the enlarged uterus pressing upward
  • A belly that feels very full or is growing quickly
  • Swelling in the legs, feet, or vulva
  • Belly discomfort, tightness, or contractions

Emergency signs — call 911

  • Signs of preterm labor: regular tightening, pelvic pressure, a constant low backache, or a change in vaginal discharge before 37 weeks
  • Your water breaking, especially with a gush of fluid
  • A sudden, rapid increase in the size of your belly with breathing difficulty
  • Reduced or absent fetal movement
  • Severe shortness of breath

Why it matters

Risks to you and baby

Preterm labor and early water breaking

The overstretched uterus is more prone to contracting early and to the membranes rupturing before term, one of the main reasons significant polyhydramnios is watched closely.

Malposition and cord prolapse

With extra room, the baby may settle breech or sideways, and when the water breaks the cord can slip down ahead of it (cord prolapse), an emergency. This raises the chance of a cesarean.

An underlying cause

Sometimes the polyhydramnios is the first clue to something else, diabetes, a fetal condition, or an infection, that itself needs attention.

Bleeding after birth

The stretched uterus may not contract down firmly after delivery, raising the risk of postpartum hemorrhage.

How it's found

How is it diagnosed?

Polyhydramnios is diagnosed on ultrasound by measuring the amniotic fluid. Once confirmed, further tests look for a cause.

Ultrasound fluid measurement

The scan reports an amniotic fluid index (AFI) or the deepest single pocket. An AFI of 24 or more, or a deepest pocket of 8 centimeters or more, confirms polyhydramnios, and the numbers grade its severity.

Detailed anatomy scan

A careful look at the baby checks for conditions that affect swallowing or the digestive tract, and, in twins, for twin-to-twin transfusion syndrome.

Maternal and fetal testing

A glucose test checks for diabetes, blood tests check for infection and fetal anemia, and sometimes an amniocentesis tests for genetic conditions or infection.

Usually in the second half of pregnancy, often as an incidental finding on a third-trimester scan, then followed with repeat measurements.

Treatment

How is it managed?

Treatment depends on severity and cause. Mild polyhydramnios is monitored and often resolves; more significant cases are treated for symptoms and any underlying reason.

Treatment paths

Mild cases need nothing beyond monitoring and often settle on their own. When a cause is found, treating it, for example controlling blood sugar in diabetes, is central. For symptomatic or severe buildup, indomethacin can reduce the baby's urine output, but only before 32 weeks because of effects on the baby's heart later. Occasionally, amnioreduction eases severe symptoms, though the fluid often re-accumulates.

Monitoring

Fluid levels, the baby's position and wellbeing, and any underlying cause are followed with repeat ultrasounds and, as needed, fetal monitoring.

Can it recur?

Whether it recurs depends on the cause. If it stemmed from diabetes, controlling blood sugar next time reduces the risk; idiopathic and anomaly-related cases are less predictable.

What you can do

Can it be prevented?

  • Control blood sugar

    Because diabetes is the leading identifiable cause, keeping blood sugar in range is the main modifiable step that can reduce excess fluid.

  • Keep your monitoring appointments

    Regular ultrasounds track the fluid level and your baby's position and growth, so any change is caught early.

  • Know the preterm labor signs

    Because it raises the risk of early labor, learning the warning signs (regular tightening, pelvic pressure, a change in discharge) lets you act quickly.

  • Report sudden changes

    A belly that grows quickly, new breathing difficulty, or your water breaking should prompt a call, as these can signal worsening fluid or the onset of labor.

Who is more at risk

Risk factors

Maternal diabetes
Gestational or pre-existing diabetes, especially when blood sugar runs high, is the most common identifiable cause of extra fluid.
Carrying identical twins
Twins who share a placenta can develop twin-to-twin transfusion syndrome, which causes excess fluid around one twin.
TTTS affects 10% to 15% of shared-placenta twin pregnancies.
A fetal condition
Conditions that make swallowing harder, such as a digestive-tract blockage or a neurological problem, can lead to fluid buildup.
Fetal anemia or infection
Fetal anemia, from causes like parvovirus B19 or blood-group incompatibility, and some infections during pregnancy can increase the fluid.
A large baby
Polyhydramnios is more common alongside fetal macrosomia, a larger-than-average baby.

Do not wait

When to call your provider or 911

  • Call right away for signs of preterm labor before 37 weeks: regular tightening, pelvic pressure, a low backache, or a change in discharge.
  • Seek care if your water breaks, especially with a large gush of fluid.
  • Contact your provider if your belly grows quickly or you develop new shortness of breath.
  • Seek prompt evaluation for reduced or absent fetal movement.
  • Report new belly discomfort, tightness, or a feeling of being overly full.

Talking to your team

Questions to ask your provider

  • How much extra fluid is there, and is it mild, moderate, or severe?
  • Have you found a cause, and do I need a glucose or infection test?
  • Does my baby's anatomy scan look normal?
  • What symptoms should make me call or come in?
  • Will I need any treatment, and when would you plan delivery?
  • Does this raise my risk of preterm labor or a cesarean?

Keep reading

More on polyhydramnios

All pregnancy guides articles

Good to Know

Polyhydramnios FAQs

Common questions about polyhydramnios, answered.

What does too much amniotic fluid mean for my baby?

Often not much, especially when it is mild and no cause is found, the most common situation. When more significantly increased, it can point to an underlying cause worth treating and raises the chance of preterm labor, an awkward fetal position, and heavier bleeding.

Why did I get polyhydramnios?

In more than half of cases there is no identifiable reason and the fluid is only mildly increased. When a cause is found, the most common is diabetes; others involve the baby, such as trouble swallowing, an infection, fetal anemia, or twin-to-twin transfusion syndrome.

Will it go away?

Mild polyhydramnios often resolves on its own with monitoring alone. When there is an underlying cause, the fluid may settle once that is addressed, for example when blood sugar is controlled. More severe cases may need treatment, but the goal is still a safe delivery.

Do I need treatment?

Not usually if it is mild, just monitoring. If it is symptomatic or severe, options include indomethacin to reduce the baby's urine output, used only before 32 weeks, and occasionally draining some fluid. Any underlying cause, like diabetes, is also treated.

Does polyhydramnios mean something is wrong with my baby?

Not necessarily. Most mild cases have no cause and a healthy baby. Because it can occasionally be the first sign of a fetal condition, your provider will do a detailed anatomy scan and other tests. If those are reassuring, the outlook is generally good.

Can it cause early labor?

It can, particularly with a lot of extra fluid, because the overstretched uterus is more prone to contracting early and to the water breaking before term. This is why significant polyhydramnios is monitored closely and knowing the signs of preterm labor matters.

What is amnioreduction?

It is a procedure to drain some of the extra fluid through a needle, similar to an amniocentesis, used for severe polyhydramnios causing symptoms like breathing difficulty. It can give relief, though the fluid often re-accumulates, so it is reserved for cases that warrant it.

Will this happen again next time?

It depends on the cause. If diabetes was responsible, controlling your blood sugar next time reduces the risk. Idiopathic cases and those from a fetal condition are less predictable. Your provider will consider what caused it this time.

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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