What Is Polyhydramnios?

Overview

Polyhydramnios is a condition where too much amniotic fluid surrounds the unborn baby during pregnancy. Whilst having too much amniotic fluid surrounding your unborn child may not seem serious at first, this can be fatal, and very sadly increase the risk of death for your unborn child. This is due to polyhydramnios being a risk factor for other conditions such preterm labour, a premature rupture of membranes and umbilical cord prolapse.¹

Which pregnancies are affected by polyhydramnios?

Approximately 20% of cases of polyhydramnios occur due to your unborn baby having congenital anomalies. However, a large proportion of pregnancies (between 60 to 70%) have no underlying cause.¹

What are the causes of polyhydramnios?

Maternal factors: gestational diabetes, obesity and Rh incompatibility

Maternal factors include poorly managed gestational diabetes, which is where, as a mother, you develop high blood sugar during your pregnancy. This can result in too much amniotic fluid surrounding your baby.²

If you are pregnant and clinically obese this can increase your risk of both gestational diabetes and polyhydramnios.³

Incompatible blood groups is another reason for polyhydramnios, which is a condition known as Rhesus (Rh) incompatibility. This can occur if you, as the mother, have the blood group Rh positive, whereas your baby has the blood group Rh negative. In turn, this causes foetal anaemia, and too much amniotic fluid surrounding your baby.

Foetal factors: foetal anomalies, twin or multiple pregnancies

Having twin or multiple pregnancies can increase your risk of having excess amniotic fluid. This is due to there being a risk of twin-to-twin transfusion syndrome. This occurs when multiple babies share a placenta, and one baby receives more blood flow via the umbilical cord than the other. This syndrome has been linked to an increase in the amount of amniotic fluid in the womb.

If your unborn baby has genetic anomalies or malformations this may increase the chance of polyhydramnios developing. Malformations include the following:²

• Myotonic dystrophy
• Oesophageal atresia
• Duodenal atresia

Clinical presentation and symptoms

Symptoms of polyhydramnios

Polyhydramnios is a condition that develops throughout your pregnancy, and it is important to note that there may not be any noticeable symptoms to keep an eye out for.

However, some of the symptoms of polyhydramnios include the following:

• Having swollen ankles or feet
• Having constipation
• Having heartburn
• Feeling breathlessness

Diagnostic methods

The most effective way of diagnosing polyhydramnios is by conducting an ultrasound and measuring the amount of amniotic fluid in your womb. The amniotic fluid index (AFI) is used to categorise the polyhydramnios as follows:

• Mild polyhydramnios: where the vertical measurement of the amniotic fluid pocket is 25-30 cm, and the deepest amniotic fluid pocket is 8 cm
• Moderate polyhydramnios: where the vertical measurement is 30.1-35cm, and the deepest pocket is 12-15cm
• Severe polyhydramnios: where the vertical measurement is greater than 35 cm and the deepest pocket is greater than 16cm

Complications and risks

Are there any complications that can occur for mother and baby if there is a polyhydramnios diagnosis?

Yes, there are complications for mother and baby, which are listed below:²

• You may go into preterm labour- before 37 weeks gestation
• You may develop maternal dyspnea
• You may have a premature rupture of membranes
• You may have an umbilical cord prolapse
• You may have a postpartum haemorrhage
• The baby may be lying abnormally, such as in a transverse lie or breech position, as opposed to head first ready for birth
• The baby may develop foetal macrosomia
• You may develop urinary tract infections

What are the implications for delivery?

Sadly, if you have been diagnosed with polyhydramnios this may affect how you give birth to your baby, and you may have to swap out plans of a natural birth or a water birth for a caesarean section (C-section).

When giving birth you would normally expect the baby to be in a head-down position ready for birth. However, due to having polyhydramnios, your baby’s position may change to a transverse lie or breech position, meaning that a C-section is needed to deliver the baby.

Polyhydramnios may cause you to have an umbilical cord prolapse, which may mean that you can’t give birth to your baby naturally. An umbilical cord prolapse is when the umbilical cord, providing blood for the baby, and nutrients such as oxygen, comes out of your vagina before your baby. Sadly, this means that the baby’s umbilical cord may become compressed, and they may receive a smaller amount of blood and oxygen than needed. A midwife or doctor may have to very gently insert a hand into your vagina to lift the baby’s head so it does not compress its cord. An umbilical cord prolapse may also result in an emergency C-section being performed to deliver the baby as quickly as possible. You may also need general anaesthetic to ensure that the baby is born quickly.

In addition, if you have a premature rupture of membranes, you may also need to have an emergency C-section to deliver the baby.⁵

Diagnosis and evaluation of the severity of polyhydramnios

How is an ultrasound used to diagnose polyhydramnios?

Diagnosis of polyhydramnios is typically done by ultrasound, as mentioned earlier, where the free pockets of amniotic fluid (where there is no foetus) are measured vertically, and their depth is also measured. The ultrasound diagnosis will allow the severity of the polyhydramnios to be categorised as mild, moderate or severe.

What is the amniotic fluid index and how is this used in diagnosis?

The amniotic fluid index helps healthcare professionals to estimate how much amniotic fluid is surrounding your baby. The amniotic fluid that surrounds your baby is known as the pocket/pockets. If your total amniotic fluid index is 25 cm or greater you will be diagnosed with polyhydramnios. Depending on both the vertical length and depth of the amniotic fluid pocket, the condition will be categorised on a scale from mild to moderate to severe.

What are the other diagnostic tests other than an ultrasound?

Other diagnostic tests include the following:

• Non-stress test: this procedure is non-invasive (it will not cut your skin or enter your body), and will measure how your baby’s heart responds when they move. A non-stress test can also be used to measure the strength of your contractions during birth. This test will help a doctor or midwife see if your baby is in distress due to receiving a low amount of oxygen.
• Biophysical test: this procedure is non-invasive and uses the non-stress test, with an ultrasound, to estimate your amniotic fluid level, and the baby’s muscle tone and breathing.
• Growth scan: this is non - invasive, and involves an ultrasound to help estimate how big your baby is. Polyhydramnios can lead to poorer outcomes if your baby is too big or too small, so early detection can help with the prognosis for your baby.

The above are standard tests, however, additional tests to diagnose polyhydramnios include the following:

• Foetal echocardiogram
• Maternal blood grouping
• Whole exome sequencing
• Maternal ToRCH screening

Management and treatment

Underlying cause treatment

If the underlying cause of your polyhydramnios is gestational diabetes, managing your blood sugar levels can help prevent the risk of polyhydramnios. Your healthcare provider should provide you with a glucose test kit to detect your blood sugar levels. This will involve pricking your finger for a drop of blood to measure your blood sugar levels. You will be advised what glucose level you should be aiming for when measuring your blood sugar levels.

If your underlying cause for polyhydramnios is rhesus incompatibility with your baby, the baby may need a blood transfusion prior to birth to treat this.

Amnioreduction

Amnioreduction involves draining a large amount of amniotic fluid from your womb, so that less amniotic fluid surrounds the baby. This procedure also restores normal amniotic pressure.⁶

Monitoring and follow-up

If you are diagnosed with mild polyhydramnios you will be asked to arrange going to an antenatal clinic, and book appointments for serial growth scans every 3 weeks. Ultimately the plan of care will be individually catered to you and your baby, depending on your needs. If you have moderate or severe polyhydramnios you will be referred to the foetal medicine unit for follow-up and monitoring. A foetal medicine consultant will arrange a plan of delivery with you.

Prognosis and outcomes

If you are diagnosed with mild polyhydramnios, and there is no known cause, your prognosis for both you and your baby is very good, and you can rest knowing that medical intervention is unlikely. However, as the severity of the polyhydramnios increases so does the prognosis for both mother and baby. Sadly, babies who have a smaller weight than what is expected do have the poorest prognosis and outcomes.¹

What is the chance of having polyhydramnios in a future pregnancy?

If you have had polyhydramnios in your first pregnancy, you are seven times more likely to develop polyhydramnios in your second pregnancy.²

Summary

• Polyhydramnios is when there is too much amniotic fluid surrounding your baby
• Known causes for polyhydramnios include when the mother has gestational diabetes, is obese or has Rh incompatibility with the baby
• Polyhydramnios may occur if your baby has foetal anomalies, or you are carrying more than one baby
• Symptoms of polyhydramnios include heartburn, constipation and breathlessness
• Depending on the amniotic fluid index, polyhydramnios is categorised as mild, moderate or severe
• Complications due to polyhydramnios include umbilical cord prolapse, premature rupture of membranes, and foetal macrosomia
• Polyhydramnios is usually diagnosed via ultrasound
• Complications with delivery may include an emergency C-section
• When you are diagnosed with polyhydramnios your pregnancy will be monitored by midwives and doctors
• The prognosis of polyhydramnios depends on the cause, and the severity of the polyhydramnios