How much amniotic fluid is normal in pregnancy?

During your antenatal appointments, one of the things your obstetrician will measure is the level of your amniotic fluid. Expectant mothers already have a lot on their plate to know, but the most common questions about amniotic fluid include what role does it play in pregnancy and is it potentially dangerous if my amniotic fluid is low? 

The short answer is that there are many levels of low amniotic fluid during pregnancy and the gestation of the baby determines what the concerns may be.

Hulda Thorey, Midwife, Former Principal of Annerley

We’ve consolidated some information that hopefully will answer your questions. Low levels of amniotic fluid generally cause no problems; however, it’s definitely something to keep an eye on when pregnant. 

What is amniotic fluid?

The amniotic fluid is the liquid surrounding the baby contained inside the amniotic sac. The fluid is clear and colourless, and early in pregnancy, it’s mostly made up of water from the mother’s body. 

As the baby develops, most of the fluid is gradually produced from the baby’s kidneys as they urinate. The baby then swallows the fluid and absorbs its contents into their bloodstream. Essentially, the pool of liquid is like an internal sea that is constantly replenishing, and the entire amount is recirculated every four to six hours. By the end of pregnancy, there may be as much as 1,500 ml of amniotic fluid. 

The function of amniotic fluid

The purpose of amniotic fluid is to provide an environment for the baby to exercise and freely move without experiencing the effects of gravity. It also helps maintain a constant temperature, provides nutrients for growth and protects the baby from external harm. 

How low is considered too low for amniotic fluid levels?

When a low level of amniotic fluid is detected, the condition is known as oligohydramnios. Generally, the amniotic fluid level is acceptable if at least one measurement is determined to be greater than 5 mm. About 8% of pregnant women are diagnosed with oligohydramnios, and it can cause complications in about 12% of the 8% detected. 

Possible causes of low amniotic fluid levels

There are some possible causes for low levels of amniotic fluid; here are just a few: 

1. Birth defects

Birth defects are one possible cause for low levels – these are generally associated with developmental issues involving the urinary tract that could cause little urine production, and therefore low levels of amniotic fluid. An ultrasonographer will have assessed the bladder and kidneys during a scan, and any concerns will be raised in the appointment. 

2. Placenta problems 

Another common cause is maternal dehydration or the placenta not providing enough nutrition to the baby. As a result, the baby stops recycling fluid, similar to when we become dehydrated and retain excess fluid.  

3. Abruption and complications

A small hole may have developed in the membranes causing the liquid to leak out. Maternal complications such as dehydration, high blood pressure, pre-eclampsia, diabetes and long-term health problems can affect the amniotic fluid levels.  

4. Due date proximity

The most common cause for a reduced amniotic fluid level is a pregnancy that is nearing or beyond its estimated due date. This occurs as a result of the declining placental function as your body prepares for delivery and birth. 

It’s important to know that the risks of oligohydramnios depend on the gestation of the baby. If the complication has occurred early in pregnancy, the concerns are more significant than towards the end. In later pregnancy, significant concerns are growth restriction, preterm birth, and labour complications.

Treatment options

The treatment for oligohydramnios depends on the age of the baby. If it’s detected early and at a significant level, there are options of care such as close monitoring to assess fetal well-being by a specialist through pregnancy ultrasounds and maternal rehydration (so drink more water). 

If low levels are detected later in pregnancy, options range from drinking more liquids to using medical interventions to increase the level of fluid in the uterus before birth. 

If amniotic fluid levels are significantly low, the method of birth will be a primary consideration. If you’re planning for a vaginal birth and your baby is showing no signs of distress or complications, before labour, it’s worth having a trial of labour with close monitoring. However, there is an increased chance with oligohydramnios that you will require a caesarian section (CS), but it’s not essential to elect immediately for your baby’s birth to be by C-section.

Help at Annerley

If you’re looking for further antenatal education, pregnancy information and support, our midwives at Annerley are here to help. You can browse our extensive maternity packages, or get in contact with us to learn more about our classes, workshops and consultations.