What is Polyhydramnios?

Polyhydramnios, or hydramnios, is a condition affecting a very small percentage pregnancies where the womb holds excessive amniotic fluid. Amniotic fluid surrounds your unborn baby and is essential for her healthy development. The fluid cushions her from external impacts, protects her from changes in temperature and infections, gives her an environment to move around in to develop her muscles and helps her to develop her digestive and respiratory organs through swallowing, digesting and recycling the fluid. Amniotic fluid is also plays a role in processing waste products from your baby.


The level of amniotic fluid usually gradually increases during pregnancy until the final few weeks. Polyhydramnios is most common in the third trimester of pregnancy and occurs when the amniotic fluid increases more quickly than usual, in acute cases very quickly and up to three times the usual volume.

What causes polyhydramnios?
In many cases it's difficult to say what causes polyhydramnios but there are a few circumstances that make the condition more likely:

  • Multiple / twin pregnancies - you're more likely to have abnormal amniotic fluid levels if you're carrying twins or other multiples. The cause of this is often twin-to-twin transfusion syndrome, where one twin has too little amniotic fluid and the other has too much.
  • Maternal diabetes - greatly increases the likelihood of polyhydramnios. Around one in ten pregnant women with diabetes will develop some degree of excess amniotic fluid.
  • Infection - certain infections such as rubella, toxoplasmosis and syphilis may lead to polyhydramnios. These can be checked for with blood tests.
  • Fetal abnormalities - in about a fifth of cases, excess amniotic fluid may build up when the baby has difficulties swallowing or digesting the amniotic fluid, preventing the fluid from being recycled. This could be caused by an obstruction in the baby's throat (such as cleft lip or palate) or gastrointestinal tract, or by a neurological problem. Polyhydramnios is also associated with problems with the baby's heart, kidneys and with chromosomal abnormalities. But, while there is an association between polyhydramnios and fetal abnormailities, do keep in mind that most women diagnosed with the condition deliver healthy babies.

How is the condition diagnosed?
Polyhydramnios is frequently picked up at a routine check. If you seem to be growing very fast for your stage of pregnancy, or if you are suffering some pregnancy discomforts particularly strongly (such as heartburn, indigestion, abdominal discomfort, shortness of breath and back pain), then your doctor may arrange an ultrasound to check the level of amniotic fluid in the womb, and to check whether there are any problems with the baby. If a problem with the baby is the cause of polyhydramnios this detailed ultrasound scan is very likely to detect it.

The ultrasound technician will measure the amount of fluid in different pockets of the womb to find your Amniotic Fluid Index (AFI), polyhydramnios is diagnosed where you have an AFI of over 24cm.

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How will polyhyhydramnios affect myself and my baby?


In milder cases polyhydramnios may present no problems at all to mother or baby, but a significant excess of amniotic fluid can cause a few temporary problems to mum although most cases don't affect the baby's health. These maternal problems relate to the extra weight of amniotic fluid you carry around that can worsen pregnancy discomforts such as