Oligohydramnios & Polyhydramnios

Question 1

Amniotic Fluid production

Answer 1

Amniotic fluid production

• First trimester: primarily derived from foetal surface of placenta, transamniotic flow from maternal compartment and secretions from the surface of body of embryo
• Second trimester: from foetal urine and lung fluid (foetal urine enters amniotic sac, and foetus begins to swallow amniotic fluid), hence disorders related to foetal renal/urinary system begin to play a role in pathology
• Third trimester: from foetal urine and secretion of lung fluid

Amniotic fluid is usually around 800ml at term; amniotic fluid index (AFI) is 10-25cm approx

• AFI < 10cm: reduced volume
• AFI < 5cm:oligohydramnios
• AFI > 25cm:polyhydramnios
• AFI: ultrasound estimation of amniotic fluid volume (derived by adding together deepest vertical pool in four quadrants of the abdomen)

Question 2

Oligohydramnios

Answer 2

Oligohydramnios – decreased volume of amniotic fluid, <5th centile, deepest pool <2cm | affects 4% pregnancies

· Risk factors for oligohydramnios

Maternal

• Uteroplacental insufficiency - preeclampsia, chronic HTN
• NSAIDs, ACEi
• Withholding NSAIDs may allow amniotic fluid to reaccumulate
• Post-term preg carry
• Leakage PPROM

Foetal

• Poor production
• Renal agenesis - no renal tissue or bladder seen on USS
• ARPKD - seen on USS as kidneys with multiple cysts and no visible bladder
• Urinary tract ab/ ob
• FGR - reduced SFH, reduced foetal movements

Pathogenesis

• Volume of amniotic fluid reflects balance between fluid production and movement of fluid out of amniotic sac
• Most common mechanisms for oligohydramnios are fetal oliguria/anuria and fluid loss due to rupture of membranes

Question 3

Signs

Answer 3

History of fluid leak PV, rupture of membranes – commonly asymptomatic

Abdominal exam – decreased fundal height, foetal parts easily palpable

Speculum – assess for membrane rupture if appropriate

Question 4

Investigations

Answer 4

USS – liquor volume, foetal anomalies

CTG– foetal wellbeing

Question 5

Management

Answer 5

Term – delivery is appropriate, IOL if no CI

Pre-term – monitor serial USS for growth, liquor volume, dopplers, regular CTGs, delivery if further abnormalities arise (note: amnioinfusion has a very limited role or effect)

Question 6

Complication

Answer 6

Labour – increased incidence of CTG abnormalities, meconium liquor, emergency CS

Neonate – pulmonary hyperplasia, limb deformities

Prognosis – increased perinatal mortality rates with early onset oligohydramnios

Question 7

Prognosis

Answer 7

Depends on cause, severity and gestational age

An adequate volume of amniotic fluid is critical to normal fetal movement and lung development, and for cushioning the foetus and umbilical cord from uterine compression → hence oligohydramnios can lead to pulmonary hypoplasia, limb deformities, Potter syndrome, in utero renal failure and cord compression

Renal agenesis and bilateral multicystic kidneys have fatal prognosis

FGR/uteroplacental insufficiency have less severe prognosis

increased perinatal mortality rates with early onset oligohydramnios