What Is Oligohydramnios?

Written by Matt McMillen, Alyssa Anderson
Medically Reviewed by Poonam Sachdev on February 26, 2025
10 min read

Oligohydramnios is a condition during pregnancy when you have too little amniotic fluid around your baby.

It occurs in about 4% of to-term pregnancies, but it becomes more common (increasing to around a 12% chance) if your pregnancy is two weeks overdue.

Low amniotic fluid levels are dangerous for your unborn child. The fluid protects your baby and gives it room for movement — letting their limbs grow and form properly. It also helps with the development of their lungs, gastrointestinal tract, and kidneys. 

You begin making amniotic fluid 12 days after your baby is conceived. A few weeks later, your baby begins to do most of that work.

“Around 16-20 weeks, the fetal kidneys start producing fetal urine, taking over the majority of amniotic fluid production until term,” says Christine Greves, MD, an obstetrics and gynecology specialist at Orlando Health in Orlando, Florida.

The amount steadily increases until it peaks at 36 weeks. Levels remain consistent for the next month and then start to go down. On average, the normal amount of amniotic fluid is about half to one quart. 

Low fluid levels are defined as having too little fluid based on how far you are in your pregnancy. Some cases can be mild, with levels slightly below average. Other cases can be severe, indicating serious complications. 

“Low amniotic fluid can be apparent as early as 16 to 20 weeks,” says Greves.

Normal amniotic fluid index

The amount of amniotic fluid can be measured in more than one way. One common measurement is called the amniotic fluid index (AFI). To obtain this, your doctor will use ultrasound images to measure the level of amniotic fluid in four different areas in your belly.

“You use the linea nigra, which is that darker vertical line in Mom's belly, to divide everything in half, and then the belly button as another half, and that creates four quadrants,” says Jacqueline Hairston, MD, an assistant professor of obstetrics and gynecology with a focus on maternal-fetal medicine at Northwestern University’s Feinberg School of Medicine in Chicago.

Once measured, your doctor adds up the different levels to get your amniotic fluid index. A normal index ranges from 5 to 25 centimeters during weeks 20 to 35 of your pregnancy. About 14 centimeters is the average. If the index falls below 5 cm, you may have oligohydramnios.

However, Hairston says some doctors use a different measurement, particularly starting at week 28, or the beginning of the third trimester. Called the maximum vertical pocket (MVP) or largest vertical pocket (LVP), it’s based on a single measurement rather than four different measurements. In this test, a normal level ranges from 2 to 8 centimeters.

Low levels of amniotic fluid might occur as isolated incidents. They can also be caused by birth defects or genetic conditions. In about 50% of all cases, the cause is unknown — this is called idiopathic oligohydramnios. 

After 16 to 20 weeks, almost all of the amniotic fluid is made of your baby’s pee — so any conditions that affect urine output may cause low fluid levels. 

Possible causes include: 

  • Carrying past your due date. In this case, the fluid loss is normal but can still be problematic.
  • Preterm rupture of the amniotic membrane. This is the cause in 37% of second and third-trimester cases. A tear allows the fluid to leak out. 
  • Placental abruption. This is the cause in 8.6% of cases. It occurs when your placenta detaches from your uterine lining.
  • Fetal birth defects. These tend to involve the kidneys or urinary tract. Your child’s kidneys may not be working correctly, their urinary tract may not have formed properly, or something may be physically blocking their urinary tract. 
  • Chromosomal abnormalities. These are found in 10% of cases detected in the second trimester.
  • Twin-to-twin transfusion syndrome. This is when nutrient distribution from a shared placenta is uneven. One twin gets too little, resulting in less amniotic fluid.
  • Maternal diabetes.
  • Chronic maternal high blood pressure.
  • Certain medications, such as angiotensin-converting enzyme (ACE) inhibitors and nonsteroidal anti-inflammatory drugs (NSAIDs).

B-cell lymphoma in the fetus

B-cell lymphoma is a cancer that starts in B-cells, a type of white blood cell called lymphocytes, which help your immune system fight disease. Though very rare, this cancer can pass through the placenta to your baby and affect their kidneys.

“The fetal kidneys produce urine, which is the leading source of amniotic fluid in the uterus,” says Greves. “The fetal kidneys may be infiltrated by the cancerous cells and can therefore affect fetal urine production.”

This results in too little amniotic fluid because the baby's kidneys don't produce enough pee.

Oligohydramnios is detected with an ultrasound. You may not know that you have the condition until you go in for a scheduled appointment and the technician notices that something is off.

Ultrasound uses sound waves to both detect amniotic fluid and measure its amount in your womb.

If your technician detects low levels, it’s usually followed up with a pelvic exam to check your amniotic sac for punctures or leaks. Other tests may be needed to figure out the cause.

Too little amniotic fluid can be a very severe condition depending on when it begins in your pregnancy. In general, the earlier it happens, the more severe the complications can be. 

When oligohydramnios is detected within the second trimester, there’s only a 10.2% chance that your baby will survive. When it occurs in the third trimester, though, your baby has an 85.3% chance of survival.  

If fluid levels are low within the first six months, possible complications include: 

  • Preterm birth 
  • Miscarriage
  • Stillbirth
  • Developmental issues with the limbs and face from increased pressure in the womb
  • Infections (if the amniotic sac has torn early)

If you get this condition in your third trimester, complications can include: 

  • Umbilical cord compression — cutting off nutrients to your baby
  • Limitations to your baby’s growth
  • Problems with lung development and breathing
  • Increased risk of a C-section
  • Risk of an early delivery

Oligohydramnios sequence

This condition is also known as Potter syndrome or Potter sequence. It occurs when the fetus’s kidneys don't develop properly, which limits how much pee they produce. Too little urine from the fetus leads to low amniotic fluid. This syndrome can affect the fetus in many ways. For example, it can cause distinct facial features, such as:

  • Widely spaced eyes
  • A receding, or set back, chin
  • A flattened bridge of the nose
  • Ears set lower than normal, lacking cartilage
  • Noticeable folds of skin in the inside corners of the eyes
  • A crease beneath the lower lip

Potter syndrome can also cause the baby to have shorter-than-normal arms and legs, joint problems, and a smaller overall size during gestation. Life-threatening complications affecting major organs such as their heart, lungs, and kidneys, can occur as well. The disease is fatal if the kidneys don't develop at all.

The first thing to be aware of is that you can have low amniotic fluid and not know it.

“Many abnormalities associated with oligohydramnios may be asymptomatic,” says maternal-fetal medicine specialist Eran Bornstein, MD, the vice chair of OB/GYN at Northwell Lenox Hill Hospital in New York City.

One key symptom that leads to a diagnosis of low amniotic fluid is fluid leaking from the vagina.

“We would only be able to diagnose it if someone complained of leaking fluid,” says Hairston. “That would prompt us to look at what’s going on with an ultrasound.” 

This can occur when the membranes in the sac that holds the amniotic fluid rupture, often referred to as your water breaking. It normally occurs after you go into labor. However, it can also happen earlier in pregnancy. This is called prelabor rupture of membranes (PROM). Hairston says this doesn’t necessarily lead to the gush of water you may see in movies or TV. “Sometimes, it can just be a slow trickle or stream,” she says. Call your doctor if you notice any such leaking.

Another important symptom that would show up on ultrasound is that your baby is smaller than normal, says Greves. If you have a smaller belly than expected for the stage of pregnancy you’re in, that also could be a symptom. You’ll need an ultrasound to evaluate the size of your baby and your amniotic fluid level, as both can influence the size of your belly, says Dr. Bornstein.

Some symptoms of low amniotic fluid may occur at different times during pregnancy.

Low amniotic fluid at 16 weeks

On an ultrasound, your doctor may see signs of poor lung development, which starts around week 16. “We would be really concerned about that,” says Hairston. You may experience leaking fluid.

Low amniotic fluid at 24 weeks

This continues to be a critical period for lung development, says Hairston, so there may be signs of that at this time. Hairston also says that your baby may show abnormal muscle or bone development and facial abnormalities at this stage.

“Without that fluid to keep the walls of the uterus away from your baby, pressure on the baby can cause developmental abnormalities,” says Hairston. This is also the time when fetal movement typically begins, she says. But you may feel it later if your baby is smaller than normal. There's a chance you may have leaking.

Low amniotic fluid at 32 weeks

Monitoring of your baby's heart may show what are called variable decelerations in the heart rate. According to Hairston, this can occur if low amniotic fluid causes the baby to rest on the umbilical cord or leads to cord compression. This would affect blood flow to your baby, lowering the heart rate. You may not feel much fetal movement, such as kicks, as normal. However, Hairston says your baby can still hiccup, which counts as movement.

“It just might not be the bigger movements that they've expected at this point,” she says. “If low fluid develops, the pattern of movement can change.”

Low amniotic fluid at 40 weeks

If low amniotic fluid develops at this stage of pregnancy, it’s likely a sign that the placenta is getting older, says Hairston, and it won’t really affect your baby or cause noticeable symptoms. However, your doctor may advise delivering your baby at that point if you have not yet gone into labor.

“We’re not going to gain much by keeping people pregnant, so usually if someone has low amniotic fluid at 40 weeks, we would recommend a birthday party,” says Hairston.

The treatment plan for your oligohydramnios depends on how low the fluid levels are and when it occurs during your pregnancy. 

While you’re still pregnant, treatment might include: 

  • Frequent ultrasounds. These could be done weekly to check your fluid levels as well as your baby’s development. 
  • Specialized ultrasounds. A technique called a Doppler ultrasound can help your doctor see your placenta. This may be needed if your baby has stopped growing. 
  • Staying hydrated. Studies indicate that maternal hydration affects amniotic fluid levels later on in the pregnancy. So, make sure you drink plenty of water. 
  • Controlling underlying maternal conditions. If you have diabetes or high blood pressure, you’ll need to take steps to get these conditions under control.  
  • Fetal interventions. These are needed if your baby’s urinary tract is blocked. 
  • Medications. These can help prepare your baby’s lungs for early delivery. 
  • Early delivery. This might be necessary to protect your baby from further complications, though it can cause complications of its own. 

If you’ve been diagnosed with oligohydramnios, you’re advised to give birth in a medical setting. This way, your medical team can prepare for — and immediately begin to treat — any of the complications that could occur. 

The exact steps that your medical team takes during and after the birth will vary from person to person and depend on the underlying cause. 

In the best-case scenario, your medical team will have identified the cause before birth, but this isn’t always possible. This means that you’ll want a variety of resources on hand to deal with any possible developmental issues your baby may have. 

For example, if a birth defect is causing the condition, your baby may need to immediately go to the intensive care unit (ICU) for treatment. Problems with their lung development or small size can also require attention in the ICU, such as intensive breath support, before your baby is allowed to go home.

When you're pregnant, you should always talk to your doctor or midwife if you have questions or concerns about your baby. 

You should get help immediately if you experience: 

  • Fluid leaking from your vagina
  • Bleeding from your vagina
  • Contractions
  • Cramps and pelvic pain
  • A decrease in your baby’s movement

Low amniotic fluid (oligohydramnios) can develop at any point during pregnancy. It is a serious condition that may harm your unborn baby. If you notice fluid leaking from your vagina during pregnancy, call your doctor right away. This could be a sign of low amniotic fluid. If you do have low amniotic fluid, expect more frequent exams and appointments during your pregnancy to monitor the health of your baby.

What is a normal AFI level?

Your AFI, or amniotic fluid index, should measure 5 to 24 or 25 centimeters from weeks 20 to 35 of pregnancy.

What is a low AFI at 36 weeks?

Your AFI is low if it drops below 5 centimeters.

What medication is used to increase amniotic fluid?

There are no medications that increase amniotic fluid.

Can drinking water increase amniotic fluid?

Possibly. Some studies have found that drinking water can boost amniotic fluid levels. IV hydration also may be helpful. However, more research must be done to confirm it’s an effective approach.