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Polyhydramnios or Hydramnios refers to too much amniotic fluid occurring in Pregnancy. There are different causes to this high amniotic fluid level during pregnancy. When left without treatment, the excess amniotic fluid has different complications on the Fetus.
Polyhydramnios is the excessive amniotic fluid level of more than 2000 ml. It has an incidence of 1:200 worldwide and usually caused by increased production of amniotic fluid or decreased consumption of amniotic fluid.
Normal Amniotic fluid levels
The average volume of amniotic fluid at term is about 800 ml, with a range of 400 to 1500 ml. Any amniotic fluid level above the upper limit of the normal is described as excessive. Clinically, volumes above 2000 ml are palpably obvious as cases of Polyhydramnios.
Normal range of Amniotic fluid according to Weeks of Pregnancy
The range of normal volumes of amniotic fluid present is wide and varies with the duration of pregnancy.
- 12 weeks gestation: Normal amniotic fluid level is 50ml
- 24 weeks gestation: Normal amniotic fluid level is 500ml
- 36 weeks gestation: Normal amniotic fluid level is 1000ml
The normal range of amniotic fluid at term in a singleton pregnancy is about 500 to 1500ml.
- Abdominal discomfort and pain: this occurs in acute hydramnios
- Excessive fetal movement
- Difficulty in breathing
- Edema and varicosities of the lower limbs
Signs of Polyhydramnios on Abdominal examination
- Over distended and shiny abdomen
- Fundal height of the uterus is higher than gestational age
- The uterus is tense and cystic
- The fetal parts are difficult to feel on palpation
- Fluid thrill can be elicited
- Fetal heart sound may be faint
- There may be mal-presentation and non-engagement of the head, these are common.
Causes of Polyhydramnios (Fetal causes)
- Increased production of amniotic fluid from high urine output in the fetus as a result of Fetal macrosomia, diabetes, recipient of twin-twin transfusion, or hydrops fetalis
- Gastrointestinal obstruction in the fetus: This may be due to esophageal atresia, duodenal atresia, small intestine or colonic obstruction or Hirschsprung’s disease
- Poor swallowing because of neuromuscular disorders or mechanical obstruction caused by Congenital anomalies such as anencephaly, myotonic dystrophy, maternal myasthenia, facial tumor, macroglossia or micrognathia. Fetal anencephaly accounts for 30-50% of the cases of Polyhydramnios as a result transudation of the cerebrospinal fluid from the exposed meninges, absence of swallowing of the liquor or fetal polyuria resulting from lack of antidiuretic hormone or irritation of the exposed centers.
- Uniovular twins could cause Polyhydramnios because of the interconnecting vascularity in the placenta, one fetus obtains more circulation so that its heart and kidneys hypertrophy leading to increased urine production. So one amniotic sac only is affected.
- Increased placental mass this could be due to: (a) edema of the placenta (arising from hydrops fetalis, severe anemia, hemoglobinopathies particularly thalassemia major and cytomegalovirus infection). Other causes of edema of the placenta are true knot of the cord (this causes obstruction of venous return with placental congestion) and Fetal liver cirrhosis as in syphilis; (b) Chorio-angioma and large placenta.
Maternal Causes of Polyhydramnios
- Diabetes mellitus due to increased osmotic pressure of the liquor amnii due to its high sugar content or fetal polyuria resulting from hyperglycemia.
- Pregnancy induced hypertension leads to edema of the placenta
- Severe generalized edema that could be caused by Cardiac, hepatic or renal disorders
Classification of Polyhydramnios
- Acute hydramnios: this type of Polyhydramnios is very rare; there is usually rapid accumulation of liquor. It occurs before 20 weeks of gestation and the commonest cause is uniovular twins, another common cause is fetal anomaly. The prognosis of acute hydramnios is poor if the patient goes into labour because the baby is invariably premature. Monochorionic twins are frequently associated with acute hydramnios.
- Chronic hydraminos: in this type, the accumulation of liquor is gradual and this occurs in late pregnancy and may end with preterm labour. When excessive amniotic fluid accumulates gradually and is noticed in the third trimester, this is referred to as Chronic hydramnios.
Diagnosis of Polyhydramnios with Ultrasound
Ultrasonography can reveal the presence of excessive amount of liquor, Multiple pregnancy, malpresentation, congenital anomalies or Intrauterine fetal death.
Treatment of Polyhydramnios depends on whether it is acute or chronic.
Management of Acute Polyhydramnios
- Place on bed rest
- Do Ultrasound to rule out twin gestation or fetal congenital anomalies
- Release amniotic fluid from uterus: (a) If the fetus is normal: release the amniotic fluid through abdominal wall with narrow-bore needle; drain fluid off slowly until the woman is comfortable drain about 500 to 1000ml fluid over 48 hours. (b) If fetus abnormal and viable consider induction of labor. If the fetus is not viable, then do Paracentesis.
Management of Chronic Polyhydramnios
- Place on bed rest
- Do Ultrasound to rule out twins and fetal abnormality.
- Do Glucose tolerance test
- Sedation if very painful
- Treat underlying maternal condition
- If fetus is normal, induce labour when indicated by fetal state not because of the Polyhydramnios
- Watch for uterine dysfunction ansd postpartum hemorrhage (PPH) after labour
Differential diagnosis of Polyhydramnios
- Causes of oversized pregnant uterus such as uterine fibroids and fetal macrosomia
- Ovarian cyst with pregnancy
- Preterm labour
- Pregnancy-induced hypertension (PIH)
- Premature rupture of membranes(PROM)
- Cord prolapse
- Abruptio placentae
- Postpartum haemorrhage (PPH)
Polyhydramnios Complications on the Fetus
- Asphyxia due to cord prolapse or placental separation