Oligohydramnios

This leaflet is to help you understand what Oligohydramnios is, what tests you need and the implication of being diagnosed with Oligohydramnios for you, your baby and your family.

What is oligohydramnios?

Oligohydramnios means that there is less amniotic fluid around your baby than expected for your stage of pregnancy. Amniotic fluid is the "water" that surrounds and cushions your baby in the uterus. Early in pregnancy, this fluid is mostly made up of water from the mother. Later, it is mainly made up of fetal urine and fluid from the baby’s lungs. The amount of fluid usually peaks around 32–34 weeks and naturally decreases near the due date.

What is the importance of amniotic fluid?

Amniotic fluid plays a vital role in helping your baby grow and develop. Amniotic fluid:

• Lets your baby move, which helps with muscle and bone development
• Protects the umbilical cord from pressure, allowing steady blood and oxygen flow
• Maintains a warm and stable environment for your baby
• Helps your baby’s lungs and digestive system develop by being swallowed and inhaled
• Acts as a cushion, protecting your baby from physical injury
• Contains fetal cells that can be tested (via amniocentesis) for certain genetic conditions

How is amniotic fluid produced?

In early pregnancy, amniotic fluid comes mainly from the mother. As pregnancy progresses, the baby starts to produce most of the fluid through urine and fluids from the lungs. The amount of amniotic fluid usually increases until about 32–34 weeks of pregnancy and then gradually decreases as the due date approaches.

How does ultrasound help with the diagnosis of oligohydramnios?

Amniotic fluid levels are usually assessed by ultrasound using one or both of these methods:

1. Amniotic Fluid Index (AFI): The uterus is divided into four sections, and the depth of fluid in each is measured. The numbers are added together. An AFI less than 5–6 cm is considered low.

2. Deepest Vertical Pocket (DVP): The largest pocket of fluid is measured. A DVP less than 2 cm suggests oligohydramnios.

Routine scans don’t always measure fluid unless there's a reason to. The best times to assess fluid are around 18–22 weeks (anatomy scan) and in the third trimester (growth scan).

Is there anything else that ultrasound can tell me about oligohydramnios?

Oligihydramnios canbe associatedtofetal anomalies (mainly fromthe urine tract) orfetal growth restriction. So, once olygohydramnios is detected, anomalies should be excluded by a detailed scan and the fetal growth assessed. Sonographic measurement of fetal size and estimations of fetal weight gain that are performed together with Doppler scans (fetal circulation assessment) may suggest the presence of oligohydramnios occurring as a manifestation of fetal growth restriction. Amniotic fluid is included in the biophysical profile which is a tool that takes together parameters as fetal movements to evaluate fetal wellbeing.

What causes oligohydramnios?

There are many reasons why amniotic fluid might be low:

• Rupture of membranes: Fluid leaks due to a tear in the amniotic sac
• Placental problems: When the placenta isn’t working well, the baby may not produce enough urine
• Fetal urinary tract problems: Such as kidney or bladder issues that reduce urine production
• Certain medications taken during pregnancy
• Post-term pregnancy: After 41–42 weeks, fluid levels often drop
• Rarely, it may have no known cause (idiopathic)

Is there anything else ultrasound can show?

Yes. In addition to measuring fluid, an ultrasound can:

• Check for fetal anomalies (especially in the kidneys or urinary tract)
• Assess fetal growth and weight
• Evaluate blood flow to the baby (Doppler scan)
• Monitor movement and overall wellbeing (part of a biophysical profile)

Oligohydramnios is sometimes a sign of fetal growth restriction. If suspected, your care provider will check for slowed growth or problems with blood flow from the placenta.

Are there possible complications?

Amniotic fluid supports your baby’s development and protects them in the womb. When it is low, there may be increased risk of:

• Preterm birth (especially if due to early membrane rupture)
• Infections (if the membranes have ruptured)
• Problems with the baby's position (e.g., breech or transverse)
• Compression of the umbilical cord
• In rare cases, problems with lung or limb development (if fluid is very low early in pregnancy)

However, when oligohydramnios is mild and appears late in pregnancy, the outlook is usually good.

What is the treatment for oligohydramnios?

There is no specific treatment that reliably increases fluid levels. Management depends on the cause and how far along the pregnancy is.

• If near full term and the pregnancy is otherwise healthy, close monitoring may be all that is needed.
• If the membranes have ruptured, your provider may monitor you for signs of infection, consider antibiotics, and watch your baby closely.
• If a urinary tract obstruction is found, fetal surgery might be considered in rare cases.
• Steroids may be given if early delivery is likely, to help your baby’s lungs mature.

Will Irequire any other tests?

Yes. Your provider will likely refer you for:

• Regular ultrasounds to monitor growth and fluid
• Doppler scans to assess blood flow to your baby
• Detailed scans of the baby’s anatomy, especially the kidneys and bladder

 

Last updated: March 2025

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Oligohydramnios

 

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