What is... Polyhydramnios


Polyhydramnios is when there is too much amniotic fluid in the womb during pregnancy. It’s relatively rare – about one in every 100 pregnancies – and for most women with this condition, it’s mild and needs no treatment. For an unfortunate few, especially when polyhydramnios is sudden and severe in early pregnancy, it could indicate more serious problems.

Amniotic fluid is the “sea” where babies begin life. It provides a warm, comfortable, safe environment for them to “swim” in and move with ease while protecting them from the outside world. At twelve weeks, this fluid is made with secretions from the umbilical cord and membranes covering the placenta, but when the baby’s kidneys start making urine at about sixteen weeks, amniotic fluid is mostly urine after that. The amount of amniotic fluid in the womb is balanced when the baby starts swallowing it around this time. Throughout the pregnancy, amniotic fluid gradually increases until there is between 500ml (two cups) and one litre at term.

How is polyhydramnios disgnosed?

Polyhydramnios is diagnosed by symptoms and on examination. Women with mild polyhydramnios may have minimal symptoms, but understandably, severe polyhydramnios can be very uncomfortable, as the woman’s belly swells beyond what it should for that stage of her pregnancy. Overstretched skin looks tight and shiny and there may be more stretch marks than usual. Other symptoms include severe heartburn, breathlessness and swollen ankles. Daily and even mundane tasks become difficult to do.

On examination, the womb is bigger than it should be for the baby’s gestational age and it may be difficult to “feel” the baby or hear the baby’s heartbeat. Excess amniotic fluid causes a “tremor” on the opposite side of the abdomen against the doctor’s hand when he flicks one side. In the final month of pregnancy, the baby’s head may not begin to descend into the pelvis as it should or the baby may not lie in the normal head-down delivery position. A sonar will confirm the diagnosis.

Why does it happen?

Amniotic fluid is renewed every five to six hours, and the amount varies according to the stage of the pregnancy. At about ten weeks when the baby starts urinating and swallowing, the amount of amniotic fluid increases from 25ml (five teaspoons) to about 400ml by 20 weeks. At 28 weeks, this amount has increased to 800ml. Amniotic fluid continues to increase until about 36 weeks after which time the amount gradually decreases to about 400ml by 42 weeks.

When babies are not swallowing properly or passing too much urine, this can cause a build-up of amniotic fluid. Polyhydramnios can also be caused by abnormalities in the baby’s oesophagus or if the baby has kidney problems. The diagnosis could also indicate asyndrome such as Down Syndrome (47chromosomes instead of the usual 46) or Edwards Syndrome (caused by an extra 18th chromosome).

More severe causes can be undetected and untreated Rh blood-group incompatibility in previous pregnancies resulting in fatal hydrops fetal is in the baby, or severe brain and spinal cord abnormalities in extreme cases.

In the mother, polyhydramnios can be triggered by diabetes mellitus, when high sugar levels cause the baby to pass too much urine. Women carrying identical twins risk a condition called twin-totwin transfer with polyhydramnios as one of the symptoms.

Women with heart and kidney conditions or infections of the womb –namely parvovirus toxoplasmosis – can cause an over-production of amniotic fluid as can choriangioma (non cancerous tumour) of the placenta.

What does it mean if you have it?

During pregnancy, women with polyhydramnios, whether acute (sudden– over a few days) or chronic (over about two weeks) should be seen more often by her caregiver to prevent complications. Mild polyhydramnios in later pregnancy (from seven months) usually resolves on its own without treatment. Acute polyhydramnios in early pregnancy however, must be thoroughly investigated as early as possible to  find the cause so that it can be treated in time.

Knowing what to expect can help the couple prepare for labour and birth. If the risks of having a natural birth are too high, the woman can prepare for a caesarean birth. She will also need to understand that if her baby is born prematurely, there may be associated risks. If severe birth defects are suspected, the mother/couple can prepare to deliver a baby with special needs and accommodate for that ahead of time.

How does it affect the mother?

It is important for her to talk to her doctor or healthcare providerabout this condition. During pregnancy, the mother/couple will understandably be anxious. They need to understand the expected prognosis so that they know what to expect, and should be advised who they can to turn to for help should the need arise.

The amount of amniotic ­fluid can be reduced by treating the cause – such as when the mother is a known diabetic. Efforts to drain excess ­fluid abdominally usually don’t work because the­ fluid is quickly replaced, and there are associated risks such as introducing infections, early labour or damaging the placenta. When polyhydramnios is mild, the woman will be carefully monitored before labour begins as well as throughout labour. If there are no problems, she can have a vaginal birth.

Women with severe polyhydramnios risk more complications such as early breaking of her waters and prolapsed cord through the vagina. Her baby may also be lying in the wrong birthing position. To avoid complications, labour may be induced or she may have a planned c-section.

After the birth, the overstretched womb can struggle to contract suf ciently to prevent haemorrhaging where the placenta comes away. When this is anticipated, precautions such as having blood on stand by should a transfusion become necessary will be taken.

How does it affect the baby?

Sixty percent of babies who survive polyhydramnios are perfectly normal. For the remaining forty percent, most babies survive their challenges in early life thanks to modern technology in high care units– sometimes even with surgical interventions before the birth. The newborn may have to be admitted into the neonatal intensive care unit (NICU), so parents should be prepared for this, especially to make sure that their medical aid covers such treatment.

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