Low Amniotic Fluid Levels – Oligohydramnios

Have you been told your baby has low amniotic fluid levels?

This article has been written in simple terms, to help you understand what that means for you and your baby.

Let’s start from the beginning.

Around day 12 after conception, the amniotic sac begins to form inside the uterus.

The amniotic sac will hold the baby and the amniotic fluid for the duration of your pregnancy.

During the first trimester, the amniotic fluid is mostly made up of fluid passed from the mother.

In the second trimester, the baby swallows and excretes the amniotic fluid.

Over time, most of the amniotic fluid will be urine created by the baby.

The lungs are also filled with amniotic fluid, and the baby will practice breathing toward the end of pregnancy.

Low Amniotic Fluid Levels

Approximately 4% of women will be diagnosed with low amniotic fluid levels (oligohydramnios) during pregnancy.

So, what causes this and how does it affect labour and birth?

Why Does The Amniotic Fluid Level Matter?

The amniotic fluid has quite a few roles and these are either for development or protection. They include:

• Acts as a cushion and protects the baby from any trauma or injury that might occur (for example, if the mother slips or experiences a sudden sharp movement, such as falling over or a car accident).
• Allows the baby to move, allowing muscles and bones to develop and grow and protecting from infection.
• Floating in the fluid also prevents compression on the umbilical cord, which would deprive the baby of oxygen.
• Keeps the baby warm and the temperature at a constant 37.6C (99.7F).
• Allows the baby to practice breathing later in pregnancy, helping the development of lung and respiratory structures.
• Swallowing and excreting the fluid encourages the development and use of the digestive system.

What Causes Low Amniotic Fluid Levels?

The most common factors causing low amniotic fluid levels are:

• Kidney or urinary tract defects in the baby
• Ruptured membranes
• Placental problems, such as placenta abruption, causing the baby to reduce urine output
• Being pregnant with twins
• High blood pressure and pre-eclampsia
• Maternal diabetes
• Maternal dehydration
• Post dates (during late term pregnancy amniotic levels naturally decrease).

What Are The Risks With Low Amniotic Fluid?

Oligohydramnios occuring in the first half of pregnancy is rare but can cause the following complications:

• Compression of the baby’s organs and limbs, resulting in birth defects (hip dysplasia, club foot)
• Premature birth (read about the signs of premature labour)
• Miscarriage
• Stillbirth

When oligohydramnios occurs in the second half of pregnancy, the following complications can happen:

• Premature birth
• Intrauterine Growth Restriction (IUGR)
• Problems with lung development
• Cord compression during labour

How Is Oligohydramnios Diagnosed?

Today, diagnosis is done by ultrasound and estimates the amount of fluid in the uterus surrounding the baby. You can read more about amniotic fluid levels here.

The amount of fluid can be measured using two methods:

• Amniotic fluid index (AFI) evaluation: four ‘pockets’ of fluid are measured by ultrasound and added up, resulting in an Amniotic Fluid Index (AFI)
• Deep pocket measurements: the single deepest vertical pocket of fluid is identified by ultrasound and measured in centimetres

When the AFI shows a fluid level of less than 5 centimetres, the absence of a fluid pocket 2-3 cm in depth, or a fluid volume of less than 500mL at 32-36 weeks gestation, then oligohydramnios is suspected. There is no current standard as to what is considered high or low amniotic fluid, and most cases are isolated – meaning there is no underlying issue causing the fluid levels to decrease.

Management Of Oligohydramnios

Induction of labour is the usual management for low amniotic fluids, regardless of whether there is a complication putting the baby at risk or not. However this may not always be the best option.

Often women who are post dates will be sent for a routine scan and a low fluid result is not surprising, given that amniotic fluid levels normally begin to decline from around 37 weeks of pregnancy.

If the pregnancy is low risk and there are no complications, there is no evidence to support induction for women with oligohydramnios.

Research shows a diagnosis of oligohydramnios in a healthy full term pregnancy isn’t linked to complications but does increase the risk of intervention.

Maternal hydration can improve amniotic fluid levels.

If you have a diagnosis of oligohydramnios in an otherwise healthy pregnancy, you might decide to have another test after 24 hours of oral or IV hydration.

Drinking electrolytes during pregnancy is valuable, no matter if you have low fluid levels or not.

In Australia, there’s an electrolyte powder (mixed into water) called Endura, which can be beneficial during and after pregnancy.

Avoid sports drinks like Powerade and Gatorade which are full of sugar.

If there is a known complication causing the low amniotic fluid, then it may be safer for your baby to be born earlier than take a wait and see approach.

Discuss your options with your care provider.

If there are low levels of amniotic fluid, your baby is not as protected against contractions during labour, especially during a medical induction.

This can result in the cord being compressed and the baby showing signs of distress due to lack of oxygen, leading to an emergency c-section.

Amniotic fluid plays a very important role in the health and development of your growing baby.

If your care provider believes you have low amniotic fluid levels, it’s essential to know if there is an underlying cause before agreeing to management.

Induction for low fluid at full term in a healthy pregnancy is associated with higher levels of interventions and possible adverse outcomes for mothers and babies. It’s important you are provided with all the necessary information to make an informed decision about your care.

Recommended Reading: Induction of Labour – The Risks of Inducing Labour