Polyhydramnios: Causes, Signs and Treatment

In this article, I shall discuss abnormality of amniotic fluids such as polyhydramnios, oligohydramnios, causes and treatment. But before then, let us consider amniotic fluid and its function for better understanding.

What is amniotic fluid?

Amniotic fluid is the fluid that surrounds and cushions the fetus in-utero, protecting and maintaining the optimal body temperature of the fetus. It is a clear alkaline and slightly yellowish liquid contained within the amniotic sac. This fluid is derived from maternal circulation across the placental membrane as well as exudates from fetal surface. The urine produced during fetal metabolism and fluid from the fetal lungs contributes to amount of the amniotic fluid.

Amniotic fluid is made up of 99% water and the remaining 1% constitutes dissolved solid substances including food particles and waste products, worn-out skin cells, vernix caseosa and lanugo, and sometime it contains meconium especially in fetal compromise or distress. The volume of amniotic fluid is about 800—1200ml at term.

Functions of amniotic fluid

  • It shields the fetus against pressure or a blow to the mother’s abdomen
  • Amniotic fluid aids in muscular development because it allows the fetus freedom to move.
  • It protects the umbilical cord from pressure thereby protecting the fetal oxygen supply.
  • It also protects the fetus from changes in temperature since liquid changes temperature more slowly than air.
  • It helps to ease the labour pain because uterine contractions are usually more painful in woman with oligohydramnios.
  • Amniotic fluid is slightly alkaline — having a pH of about 7.2.  Checking (Nitran test) the pH of the fluid at the time of rupture with litmus paper enables the midwife to differentiate it from urine, which is acidic (pH 5.0–5.5). If it’s urine, it turns litmus paper to red, indicating its acidic pH while that of amniotic fluid turns blue —showing alkalinity.

However abnormality does occur in amniotic fluid which includes polyhydramnios (hydramnios) and oligohydramnios.  And let’s consider hydramnios today.

What is Polyhydramnios?

Polyhydramnios (hydramnios) occurs when there is excess amount of amniotic fluid in the amniotic sac.   It is the amount of amniotic fluid that exceeds 1500ml but it may not be clinically apparent until it gets to 3000ml (that is, 95% above the amniotic fluid index).

How common is hydramnios?

Polyhydramnios is considered to be more common in multiparous than in nulliparous women. And it occurs one in every 250 pregnancy.

What are causes of Polyhydramnios?

 The aetiology of polyhydramnios is not known but has been attributed to:

  • Fetus-to-fetus transfusion syndrome
  • Multiple pregnancy, especially in the monozygotic twins(uniovular twins)
  • Maternal diabetes mellitus (gestational diabetes mellitus) because hyperglycaemia causes excessive fluid shifts into the amniotic space.
  • Congenital fetal anomalies especially of CNS e.g. anencephaly, encephalomeningocele, open neutral tube defects/spinal bifida. Normal foetus swallows liquor amnii but anencephalic foetus is incapable of swallowing liquor amnii and thus, the hydramnios.
  • Oesophageal atresia, (oesophageal atresia means fetal inability to swallow liquor amnii.)
  • Fetal anaemia and severe erythroblastosis fetalis
  • Severe pre-eclampsia
  • Congestive cardiac failure
  • Infections(e.g. syphilis or parovirus infection)
  • Maternal alloimmunization
  • Vascular abnormality of the chorion e.g. Chorioangioma, a rare tumour of the placenta
  • Fetal and placental tumor (rare)
  • Rarely, Rhesus iso-immunization
  • Hydrocephalus, club-foot and hare-lip are rare causes of hydramnios
  • Idiopathic

Note: Chorioangioma is a small tumor growing from a chorionic villus and consist of enlargement of the blood vessels and connective tissue

Classification of hydramnios

Polyhydramnios is classified based on:

Time of its onset

  • Acute hydramnios
  • Chronic hydramnios

Its degree or severity

  • Mild hydramnios
  • Moderate hydramnios
  • Severe hydramnios

 Acute hydramnios:

This is a rare form of polyhydramnios that develops suddenly, usually around 20 week’s gestation. It is characterised by rapid increment of uterine size reaching the level of xiphisterneum within 3 to 4days and the woman’s complaint of severe abdominal ache. Fetal anomalies and monozygotic twins are the commonest risk factors or causes of acute polyhydramnios

What are signs and symptoms of acute hydramnios?

Acute high liquor amnii is associated with the following:

  • Rapid enlargement of the abdomen at the fourth month
  • Abdominal girth is in excess of 100cm
  • Often associated with gross congenital abnormalities and occasionally with uniovular twins
  • Severe abdominal discomfort and breathless (dyspnoea)
  • Oedema of the ankles and legs
  • If varicose veins are present, they become more troublesome
  • Digestive discomfort and Vomiting
  • Very tense abdomen, difficult to palpate
  • Difficult to feel the fetal part.
  • Abdomen may be woody hard. This finding coupled with severe abdominal pain may make the midwife to suspect concealed abruptio placentae.

Chronic polyhydramnios:

This is a gradual accumulation of amniotic fluid, often noticed in the third trimesters (about 30 weeks’ gestation). It is most common type of amniotic fluid abnormality.

What are signs and symptoms of chronic hydramnios?

  • Abdominal girth increases but gradual
  • No acute symptoms of dyspnoea, pain, and discomforts
  • Dyspnoea, abdominal discomfort and oedema of the legs may be present in severe cases
  • Varicose veins if present may be painful.
  • Difficulty to palpate fetus or hear the fetal sounds
  • Abdominal girth is in excess of 100cm
  • And fluid thrill may be elicited.

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Polyhydramnios

How to diagnose Hydramnios

Maternal history: The woman may complain of abdominal discomfort, over-distension or excessive fetal movements.  In an acute polyhydramnios, she may complain of vomiting, abdominal pain, heartburn, indigestion, constipation and difficulty in breathing —which are all exacerbated by symptoms associated with pregnancy.

Abdominal examination:

 On inspection: the fundal height is obviously exceeds the expected gestational age. The uterus is globular in shape instead of normal ovoid shape.

On palpation: the midwife feels tense uterus and may find it hard to palpate the fetal part.

On auscultation: the fetal heart sounds may be hard to hear due to the excessive liquor amnii.

Differential diagnosis for hydramnios

Multifetal pregnancy, even full bladder and other related causes of large for dates pregnancy like co-existing fibroids, or ovarian cyst should be looked into it. The midwife should also consider hydatidiform mole, fetal macrosomia and wrong dates for their absolute exclusions.

Ultrasound screening:  a non-invasive procedure will confirm the diagnosis hydramnios by ruling out or revealing the presence of multiple pregnancy, fetal abnormalities, fetal macrosomia, ovarian cyst, hydatidiform mole and uterine fibroids. The ultrasound scan usually shows that the sum of the liquor depth in each of the four quadrants of the uterus (Amniotic fluid Index, AFI) greater than the 95th centile for gestational age, which is a diagnostic confirmation of hydramnios.

Abdominal x-ray: This may reveal skeletal fetal anomalies and exclude multiple pregnancies. However, it must only be used in where ultrasound scan is not available because of the risk factors associated with x-ray radiations.

How to manage hydramnios

This depends on the condition of the woman and fetus, including the cause and degree of the hydramnios and the gestational age (GA) of the pregnancy.

Asymptomatic hydramnios especially where there are no associated fetal abnormalities need no treatment.

But when there are gross anomalies of the fetus, the woman has to choose either to electively induced the labour or carry the fetus to term if the fetus has surgicable or operatable deformity like oesophageal atresia which can be managed immediately in neonatal surgical unit.

In symptomatic hydramnios where the gestational age is beyond 37weeks with serious maternal distress, labour can be safely induced. Prior to induction, supportive treatment such as encouraging the woman to adopt upright position which relieves any dyspnea and antacids may be administered to alleviate heartburn and nausea.

In case of hydramnios where there’s serious maternal distress with GA less than 37 weeks of gestation and no fetal malformation, therapeutic abdominal amniocentesis or amnioreduction could be performed.

This may be repeated severally where necessary in order to achieve optimal outcome. The technique is associated with the risks of infections, preterm labour, disseminated intravascular coagulopathy (DIC) and perforation of the fetal vessels with resultant bleeding into the Amniotic sac particularly when performed under poor aseptic techniques and without ultrasound guidance.

What are dangers of sudden rupture of membranes in cases of hydramnios?

  • Prolapse of the cord
  • Placental separation resulting in antepartum haemorrhage

After delivery, the patient may have postpartum haemorrhage because of attendant uterine inertia due to the over-distention of the uterus.

Note; abdominal paracentesis should be carefully performed as frequently as the occasion demands. If the fetus is mature, labour may be induced by a slow, controlled forewater or hindwater rupture of membranes.

Complications of hydramnios

  • Maternal urinary tract infection: This is related to ureteric obstruction by the overweighing uterus. Obstructed ureters bring about urinary stasis –breeding ground for infection.
  • Unstable lie and malpresentation: Related to excessive fetal movements aided by hydramnios
  • Umbilical Cord presentation
  • Umbilical Cord prolapse following the artificial rupture of membranes
  • Placental abruptio accompanying rapid release of the liquor.
  • Preterm labour
  • Postpartum haemorrhage related to uterine atony
  • High incidence of caesarean birth and perinatal mortality rate.

Prevention of hydramnios

No specific way for preventing hydramnios. However, the two methods of prenatal treatment of polyhydramnios are amnioreduction and medical treatment with non-steroidal anti-inflammatory drugs (NSAIDs e.g. ibuprofen).

 Prenatal administration of NSAIDs such as ibuprofen or Diclofenac has been found to reduce amniotic fluid volumes but these are not without side effects. As per Hamza et al., 2013, some experimental therapeutic studies are still trial that would alter fetal diuresis and in turn control polyhydramnios 

The midwife managing woman in labour with hydramnios should anticipate postpartum haemorrhage due to uterine over-distension and get everything handy should emergency arise.

The baby should be thoroughly examined at birth to detect any abnormality and initiate prompt care.

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