Polyhydramnios

What is polyhydramnios?

Polyhydramnios is a condition where the water around your baby, also called amniotic fluid, is increased during pregnancy. Amniotic fluid mostly comes from your baby’s urine. It helps to protect, cushion and support your baby as they grow and develop.

Your baby also swallows some of this fluid, which is then absorbed and passed out again as urine. This helps keep the amount of fluid in balance. Sometimes this balance changes, leading to too much or too little fluid. When there is too much fluid, this is called polyhydramnios.

Polyhydramnios affects about 1–4% of pregnancies. It usually develops in the second or third trimester and is diagnosed by measuring the amount of amniotic fluid during an ultrasound scan.

Polyhydramnios can be classed as mild, moderate or severe depending on the amount of amniotic fluid seen during your ultrasound scan.

Causes of polyhydramnios

In most cases, polyhydramnios is mild and the cause is unknown. This is called idiopathic polyhydramnios. It may simply be a normal variation or a temporary finding.

Sometimes, polyhydramnios can be associated with conditions affecting the mother, birthing person or baby. Severe polyhydramnios is more likely to have an underlying cause.

If your healthcare team suspects polyhydramnios, they will offer detailed ultrasound scans and may suggest additional tests to check for a cause and monitor you and your baby’s wellbeing.

Polyhydramnios can develop in two main ways

  • Your baby swallows less fluid than usual.
  • Your baby produces more urine than usual.

Possible causes include

  • A problem with your baby’s swallowing or digestion, especially affecting the brain, stomach or bowel.
  • Your baby having a chromosomal abnormality, such as Down’s syndrome, Edwards’ syndrome or Patau’s syndrome, or another genetic condition.
  • Fetal anaemia, when your baby has too few red blood cells.
  • Infections during pregnancy.
  • Being pregnant with more than one baby.
  • Gestational diabetes or other maternal medical conditions and medications.

Complications associated with polyhydramnios

Most people with polyhydramnios have healthy pregnancies and babies. However, having more amniotic fluid can occasionally increase the risk of certain complications.

These may include:

  • Discomfort or shortness of breath caused by the womb being more stretched than usual.
  • Early rupture of the membranes, which can lead to premature birth before 37 weeks of pregnancy.
  • Your baby changing position frequently inside the womb, known as unstable lie.
  • Umbilical cord prolapse, when the cord slips into the birth canal after the waters have gone and before the baby.
  • Placental abruption, when the placenta separates from the womb before birth. This is rare.
  • Increased bleeding after birth, known as postpartum haemorrhage.

Can polyhydramnios be treated?

The aim is to monitor you and your baby, ease any discomfort and manage the underlying cause if one is found. Treatment depends on the severity of the condition.

  • Mild cases usually do not need treatment beyond regular monitoring of your baby’s wellbeing, including ultrasound scans.
  • Severe cases may need treatment to reduce the amount of amniotic fluid and help prevent early birth.
  • If there is a chance your baby might be born early, steroid injections may be offered to help your baby’s lungs mature before birth.

Amnioreduction

One treatment for severe polyhydramnios is called amnioreduction. This involves using a thin needle to remove some fluid from the womb, guided by an ultrasound scan.

Amnioreduction can help ease discomfort and reduce the risk of complications, but it may also trigger labour. Sometimes, the procedure may need to be repeated.

Outlook for polyhydramnios

When polyhydramnios is mild and happens on its own, the outlook is very good and most pregnancies result in healthy babies.

When polyhydramnios is linked to another condition affecting the mother, birthing person or baby, the outlook will depend on the underlying cause.

Your healthcare team will discuss your individual situation with you and provide ongoing support and recommendations about the timing of birth.

When to contact your midwife or maternity unit

You should contact your midwife or maternity unit straight away if you experience any of the following:

  • Signs or symptoms of preterm labour, such as regular contractions or back pain.
  • Vaginal bleeding.
  • A gush of fluid from the vagina or a popping sensation, which could mean your waters have broken.
  • Abdominal pain.
  • A sudden increase in the size of your abdomen.
  • Breathlessness.
  • Any concerns about your baby’s movements.

We understand that this can be a worrying time. Please contact the hospital for assessment if you have any concerns.

The Maternity Assessment Suite provides 24/7 care from 20 weeks at Chelsea and Westminster Hospital and from 18 weeks at West Middlesex University Hospital. Please call the unit to discuss any concerns and we will advise you if you need to attend one of our units.

Maternity Assessment Suite contact numbers

  • Chelsea and Westminster Hospital: 020 3315 6000, option 1
  • West Middlesex University Hospital: 020 8321 5839

Further information

Contact information

Chelsea and Westminster Hospital

Antenatal Clinic
369 Fulham Road
London
SW10 9NH

T: 020 3315 6000

West Middlesex University Hospital

Queen Mary Maternity Unit
Twickenham Road
Isleworth
Middlesex
TW7 6AF

T: 020 8560 2121