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Amniotic fluid

4-minute read

What is amniotic fluid?

Amniotic fluid is the liquid that surrounds your baby in the uterus during pregnancy. It is contained in the amniotic sac.

How is amniotic fluid produced?

Amniotic fluid starts to form in the first few weeks of pregnancy.

Your baby produces most of this fluid themselves through their urine and lung secretions. The amount of amniotic fluid around your baby usually increases throughout pregnancy and is thought to reach its highest amount (volume) early in the third trimester.

Why is amniotic fluid important during pregnancy?

Amniotic fluid has a few important functions that help to support your baby’s growth and development.

The amniotic fluid helps:

  • your baby to move around in your uterus
  • your baby’s lungs, digestive system and muscles to develop
  • maintain a normal temperature around your baby
  • cushion and protect your baby and their umbilical cord from pressure or outside injury

How is amniotic fluid assessed?

Amniotic fluid can be assessed and measured using ultrasound. The ultrasound probe will be placed on your tummy and the healthcare professional will look for pockets of amniotic fluid around your baby.

Once these pockets of fluid are found, the depth of the fluid is measured to give an indication of the overall fluid volume. The amount of fluid is usually described in centimetres.

What do the results of this test mean?

The amount of amniotic fluid around your baby provides some information about your baby’s wellbeing. Too much or too little fluid can be associated with pregnancy complications and can sometimes signal that there is a problem.

For this reason, the amount of amniotic fluid is often measured during your routine pregnancy ultrasounds.

How much fluid is normal?

The amount of amniotic fluid that you can expect in pregnancy depends on how many weeks pregnant you. The amount will vary from person to person and in each pregnancy.

How much amniotic fluid is considered normal varies a lot, and the reference range used to determine this depends on how your healthcare provider does the assessment.

For this reason, it’s best to speak with your midwife or doctor to understand the assessment and results.

What if the amount of fluid is not normal?

In a small number of pregnancies, the amount of fluid around the baby may be higher or lower than expected. This may be because of a pregnancy complication and can sometimes indicate that there is a problem, although in some cases a cause may not always be found.

  • Oligohydramnios is the medical term used to describe having low or not enough amniotic fluid.
  • Anhydramnios is the medical term used to describe when there is no amniotic fluid seen on an ultrasound.
  • Polyhydramnios is the medical term used to describe having too much or more fluid than expected.

What a high or low fluid volume means for you and your baby depends on a number of factors, including the cause (if known), the severity of the finding and how far along you are in your pregnancy.

If you have an amniotic fluid volume that is considered too high or too low, your doctor or midwife will explain what this means for you, including the likely causes and how to manage this.

If the amniotic fluid volume is not within the expected range, it is very likely that you have not done anything to cause this. However, keeping healthy and active in pregnancy will help both you and your baby.

Speak to a maternal child health nurse

Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: November 2022


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