What Is Oligohydramnios 

Overview

Oligohydramnios occurs when there is less amniotic fluid surrounding your baby than expected for their gestational age. Amniotic fluid is the water-like substance that cushions and protects your baby, giving them the best possible environment to develop in. This watery fluid resides in the amniotic sac, helping your baby’s lungs, kidneys, and gastrointestinal tract develop. 

In most pregnancies, the amount of amniotic fluid will continue to increase during gestation, until about 33 weeks when it starts to level off. Pregnant women will normally have approximately 500 ml of amniotic fluid at 32-36 weeks of gestation.¹ Complications can arise if there’s too little amniotic fluid surrounding your baby. Oligohydramnios affects around 4% of pregnant women and is most commonly seen during the last trimester. 

What causes oligohydramnios?

Both maternal and foetal factors can cause oligohydramnios. 

Foetal causes

The foetal causes are most commonly related to your baby’s urinary system. This is the system that filters the body’s substances through the kidneys and produces urine. During gestation, the baby will swallow some of the watery fluid (amniotic fluid) surrounding them, which is processed by the kidneys, and eventually reaches the bladder. The bladder is emptied, pushing this fluid back into the amniotic sac. This cycle then repeats itself.

This process can be disrupted, and this is how oligohydramnios occurs. If the kidneys aren’t functioning properly, or there is a blockage in the tubes connecting the kidneys to the bladder, it will lead to less amniotic fluid being produced. 

Premature rupture of membranes

The sac surrounding your baby may also rupture prematurely. This is more commonly referred to as your water breaking. This will reduce the amniotic fluid surrounding your baby. If you are close enough to term, then your healthcare providers may choose to induce labour early.² 

Placental insufficiency

Placental insufficiency is a condition that occurs when the placenta, the organ responsible for supplying nutrients and oxygen to the developing foetus during pregnancy, doesn't function as well as it should. 

Think of the placenta as a special bridge between a mother and her baby during pregnancy. This 'bridge' is essential because it's the baby's main source of food and oxygen. This can happen for various reasons, such as problems with the blood vessels in the placenta or issues with how the placenta attaches to the uterus.

Placental insufficiency means the placenta isn't providing enough nutrients and oxygen to the growing baby. If the baby isn't getting the right amount of 'building blocks' for proper development, this will start to affect the baby's growth and development. 

Other causes

• The pregnancy going past the due date
• Hypertension or preeclampsia 
• Diabetes 
• Dehydration
• Twin-to-twin transfusion syndrome
• Intrauterine growth restriction

If you’ve had low amniotic fluid in previous pregnancies, then you are at a higher risk of it occurring again. 

Symptoms 

Not all symptoms are the same for all pregnancies, but here are some common symptoms: 

• Fluid leaking out of your vagina
• You aren’t feeling your baby move frequently 
• You haven’t gained weight recently
• Your uterus is small

If you experience any of these symptoms, we recommend you see your healthcare provider. Bear in mind that these symptoms are fairly non-specific, meaning they may be indicative of different conditions too. 

What are the complications?

Intrauterine growth restriction

Oligohydramnios may result in intrauterine growth restriction (IUGR), meaning the baby may not reach the expected size for its gestational age. This is usually due to not having enough space inside the uterus to grow, which can affect the baby's overall development.

Higher risk of birth defects

In severe cases of oligohydramnios, there is a higher risk of birth defects occurring, particularly in mothers diagnosed with oligohydramnios in the first two trimesters of pregnancy. 

Preterm labour

Oligohydramnios is often linked to an increased risk of preterm birth. As mentioned earlier, if your waters break early, labour is likely to occur shortly after. Babies born prematurely may face challenges related to lung development and may require specialised care in a neonatal intensive care unit (NICU).

Risk of cord compression

A reduced amount of amniotic fluid can increase the risk of the umbilical cord becoming compressed. This is the cord that connects your baby to the placenta, which provides them with oxygenated blood and nutrients. If direct pressure is applied to this cord, it may compromise the baby's oxygen and nutrient supply, leading to potentially serious complications.

Umbilical cord compression can sometimes be detected through changes in the foetal heart rate, signalling distress and prompting the need for medical intervention.

How is oligohydramnios diagnosed?

Your healthcare provider will measure the volume of amniotic fluid in your uterus using a device called an ultrasound probe. It’s a simple investigation, where they will apply some jelly to your bump and then use a probe to get a view of your baby and the amniotic fluid around them. 

There are two ways they might measure the amount of amniotic fluid. The amniotic fluid index (AFI) and the maximum pool depth. Both these techniques look at how deep the fluid is around your baby to ensure everything is just right for the baby's safe and healthy development.³

What is the treatment of oligohydramnios?

The treatment you receive will be highly dependent on the cause of your oligohydramnios and how far along you are in your pregnancy. The main aim is to keep you and your baby safe. 

Before term 

Once a diagnosis of oligohydramnios has been made, ongoing checkups are important to assess the severity of the condition. Your healthcare providers will be looking at how your baby is growing, as well as monitoring the volume of amniotic fluid.

There’s also evidence to show that treating maternal dehydration can increase the amniotic fluid volume by 30%.⁴ 

At term

Delivering your baby, provided it is safe to do so, will be the most appropriate management. It may be that your healthcare providers induce labour early if they think your baby may be at risk of further complications. 

Summary 

Oligohydramnios is a condition characterised by lower-than-expected levels of amniotic fluid surrounding the baby in the uterus. Amniotic fluid is crucial for the baby's protection and development, aiding in the growth of the lungs, kidneys, and gastrointestinal tract.

Symptoms of oligohydramnios include fluid leakage, decreased foetal movement, lack of recent weight gain, and a small uterus. Complications may include intrauterine growth restriction (IUGR), an increased risk of birth defects, preterm labour, and the risk of umbilical cord compression.

Diagnosis involves ultrasound measurements, specifically the amniotic fluid index (AFI) and maximum pool depth. Treatment varies based on the cause and gestational age, ranging from close monitoring to early induction of labour. 

Prevention is challenging, but early detection through regular check-ups is crucial. Attending prenatal check-ups is a key factor in ensuring early detection and appropriate management.

FAQs

What is oligohydramnios?

It is a condition that occurs during pregnancy when there is not enough amniotic fluid surrounding the foetus.

What causes oligohydramnios?

There are several factors that can contribute to the development of this condition, including maternal dehydration, foetal abnormalities in the kidneys/urinary tract, placental issues, pregnancies that are post-term, or maternal conditions such as hypertension and preeclampsia.

How is oligohydramnios diagnosed?

Typically via ultrasound examination. This allows healthcare providers to measure the amniotic fluid index where a low AFI indicates oligohydramnios?

How can I prevent oligohydramnios?

Unfortunately, there isn’t much you can do to prevent oligohydramnios. Being honest with your doctors about any symptoms you’re experiencing and attending your checkups will ensure it can be picked up early. 

What symptoms should I be looking out for?

It is important to note that this condition doesn’t have specific symptoms, and if there are symptoms, they tend to not be noticeable, but some things you should look out for and mention to your healthcare provider are decreased foetal movements, contractions or abdominal discomfort, and fluid leaking out of your vagina.

How is oligohydramnios treated?

Underlying causes of the condition are what determine the treatment for oligohydramnios. In some cases treating maternal dehydration can create a considerable improvement to the condition. In most cases, treatment is reliant on regular monitoring of birthing parent and baby, and in severe cases, early delivery may be considered if it is safe for both parent and baby.

Will my baby survive oligohydramnios?

Yes, in most cases babies are born healthy and live normal lives. A reduced amount of amniotic fluid can be severe, but it is highly treatable. Ensure that you attend all your prenatal checkups to make sure any potential issues are detected. 

What are the potential complications for the birthing parent during pregnancy if they have oligohydramnios?

Some complications include umbilical cord compression, increased risk of uterine rupture, and complications during labour and delivery.

Can oligohydramnios resolve on their own?

In some mild cases, yes oligohydramnios can resolve on its own. However, you must still mention any symptoms to your healthcare provider and make sure you attend your regular check ups to ensure the wellbeing of both the baby and the birthing parent.