Oligo/Polyhydramnios

Oligohydramnios

This is the term used to describe an abnormally low level of amniotic fluid during pregnancy

– It is characterised by having less than <500ml at 32-36 weeks and amniotic fluid index (AFI) <5th percentile

– It can lead to abnormal foetal presentations and underdevelopment of foetal parts

Causes:

– Low production of foetal urine –> Renal agenesis (Potter’s syndrome), dysplastic kidney, obstructive uropathy

– Poor Placental diffusion –> Pre-eclampsia

– Leakage of amniotic fluid –> Premature rupture of membranes

Complications:

– Abnormal lie and development

– Poor respiratory development –> amniotic fluid is needed for maturation of the alveoli, so infants are born with severe respiratory distress

– Foetal muscle contractures (as amniotic fluid allows the fetus to move its limbs in utero)

Diagnosis:

– Ultrasound is investigation of choice (shows level <5th centile)

Management:

– Increase maternal hydration (+ amniofusion during labour to stop cord compression) 

Polyhydramnios

This is the term used to describe an abnormally high level of amniotic fluid during pregnancy

– It is used when the amniotic fluid index is above the 95th centile for gestational age

– It causes over-distension of the uterus which can lead to preterm labour and other complications

Causes:

– It is idiopathic in the majority of cases

– Congenital infection

– Twin-to-twin transfusion syndrome –> leads to oligohydramnios for one and polyhydramnios for the other

– Decreased swallowing of fluid –> foetal oesophageal/duodenal atresia or CNS abnormalities

– Increased production of fluid:

– Macrosomia (big babies produce more urine)

– Maternal lithium ingestion (leads to foetal diabetes insipidus)

– Adenomatoid malformation of the lung which leads to increased foetal lung secretions

Complications:

– Preterm delivery (due to over-distension of the uterus)

– Malpresentation (fetus has more room to move within the uterine cavity) increasing risk of breech delivery

– Post-partum haemorrhage (as the uterus has to contract move to compress the dilated blood vessels)

– Gastro-oesophageal reflux for the mother

Diagnosis:

– Ultrasound is investigation of choice (shows level >95th centile)

Management

– Antacids to relieve heartburn and nausea for the mother, monitor complications for fetus