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Polyhydramnios: Excessive Amniotic Fluid

She was breathless when she shuffled her way slowly into the consultation room. Her feet were swollen from ankles up to the legs. After climbing up the examination couch with some difficulty and pointing at her huge tummy, she asked, “Doc, can I deliver my baby soon?”

N,32 and a first-time mum was at her 36 weeks of gestation. There was no history suggesting viral infection during her antenatal period. She was not a carrier of thalassemia and her blood group was O Rh+ve. Glucose tolerance test was normal and blood tests for rubella( German Measle), syphilis and toxoplasma were negative

Non-invasive prenatal test (NIPT) was normal. Ultrasound scan for foetal anomalies at 22 weeks gestation did not reveal any obvious structural defects. Foetal weight was average and the amniotic fluid index (AFI) was normal. However, during the growth scan at 32 weeks of gestation, the amniotic fluid was noted to be excessive with an AFI of 28.

N was suffering from a condition called polyhydramnios.

What is polyhydramnios?

Amniotic fluid is a clear liquid that surrounds the foetus inside the womb. It promotes foetal growth, helps develop its lungs, keeps a constant temperature around the baby and acts as a protective cushion for the baby.

The amount of amniotic fluid is greatest at about 34 weeks of gestation when it averages 800ml. At 40 weeks of gestation, the level drops down to about 600ml.

Polyhydramnios occurs when the volume of amniotic fluid exceeds normal levels. It is present in about 1 to 2 percent of pregnancies. Most cases are usually mild and result from a gradual buildup of amniotic fluid during the second half of pregnancy. But in severe cases, major complications to the mother and baby can appear.

What are the causes of polyhydramnios?

In 50-60% of severe cases, the cause is unclear. Some of the known causes include:

· A birth defect that affects the baby's digestive or central nervous system

· Maternal diabetes before or during pregnancy

· Big baby

· Twin pregnancy

· Foetal anaemia: A lack of red blood cells in the baby

· Blood incompatibilities between mother and baby

· Infection during pregnancy

What are the symptoms of polyhydramnios?

Mild polyhydramnios is generally innocuous. In severe case, the symptoms include

· Shortness of breath or discomfort in breathing

· Swelling in the lower extremities and abdominal wall

· Uterine discomfort or contractions

· Difficulties or discomfort in urination

· Swollen vulva

How is polyhydramnios diagnosed?

Polyhydramnios is diagnosed by ultrasound examination. There are two ways of measuring amniotic fluid: amniotic fluid index (AFI) or maximum pool depth (MPD). They have fairly similar diagnostic accuracy. However, AFI is more commonly used.

AFI is calculated by measuring the maximum vertical pocket of fluid in four quadrants of the uterus and adding them together. An AFI of 25 cm or more indicates polyhydramnios.

Complications of polyhydramnios

Polyhydramnios is associated with the following complications:

  • Prematurity: excess amniotic fluid can trigger preterm labour or premature rupture of membranes and increase the chances of a baby being born prematurely.

  • Big baby: Polyhydramnios is commonly associated with big babies. This may lead to increased incidence of caesarean section and /or birth trauma during vaginal delivery.

  • Placental Abruption: The placenta prematurely separates from the wall of the uterus before delivery resulting in foetal asphyxia

  • Foetal Malposition: With too much fluid in the womb the baby may assume various positions instead of the normal head-down position during delivery.

  • Umbilical Cord Prolapse: This is the most dangerous complication when the umbilical cord drops into the vagina ahead of the baby.

  • Postpartum haemorrhage: Heavy bleeding can occur from lack of uterine muscle tone after delivery

How is polyhydramnios managed?

In the majority of cases, no medical intervention is required.

If the mother feels breathless, drainage of the amniotic fluid or amnioreduction can be considered. However, this may cause infection and placental abruption.

Medications like indomethacin may be used to reduce foetal urine output. But due to the risk of foetal heart problems, it is not recommended after 32 weeks of gestation.

Timing and mode of delivery will depend on the stage of pregnancy, foetal position and presence of complications.

As the foetus was lying horizontally across the mother’s abdomen (transverse lie) N was advised to have a caesarean section. A healthy baby boy weighing 3 kg was delivered. A nasogastric tube was passed down the baby's food passage to ensure there was no blockage before feeding. Both the mother and child were discharged well 3 days after the operation.

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