Oligohydramnios

Oligohydramnios is an amniotic fluid volume that is lower than expected for gestational age. Oligohydramnios may occur as an isolated finding or in association with fetal or maternal conditions. Fetal causes include renal tract abnormalities, chromosomal abnormalities, and congenital infections. Maternal causes include placental insufficiency and premature rupture of the membranes. Oligohydramnios is often an incidental finding on routine prenatal ultrasound but should be suspected if fundal height is less than expected for gestational age or if premature rupture of membranes occurs. An obstetric ultrasound with a deepest vertical pocket < 2 cm or an amniotic fluid index < 5 cm confirms the diagnosis. Specialist referral is indicated for further evaluation (e.g., underlying causes, associated fetal complications), antepartum surveillance, and possible interventions (e.g., amnioinfusion, planned delivery). Management is based on the gestational age, underlying cause, and severity. Complications include fetal growth restriction, pulmonary hypoplasia, intrauterine fetal demise, Potter sequence, and umbilical cord compression.

Oligohydramnios may occur as an isolated finding or as a result of underlying fetal or maternal factors. ^[1][2]

Fetal factors ^[2]

• Congenital anomalies of the kidney and urinary tract
  • Urethral obstruction (e.g., posterior urethral valves)
  • Bilateral renal agenesis
  • Autosomal recessive polycystic kidney disease (ARPKD)
• Twin-to-twin transfusion syndrome (donor twin) ^[3]
• Chromosomal abnormalities (e.g., aneuploidy)
• Congenital infections (e.g., TORCH infections) ^[4]

Oligohydramnios is associated with conditions that cause decreased fetal production of urine. ^[2]

Maternal factors ^[2]

• Placental insufficiency ; ^[5]
  • Hypertensive disorders of pregnancy
  • Late-term pregnancy; and postterm pregnancy
• Premature rupture of membranes

Oligohydramnios is diagnosed with an obstetric ultrasound. ^[5]

• Indications ^[1][5]
  • Routine prenatal ultrasound or antepartum fetal surveillance
  • Low fundal height for gestational age
  • Decreased fetal movement ^[1]
  • Signs of abnormal rupture of membranes
• Findings ^[6][7]
  • Low amniotic fluid volume determined by either ^[5][6]
    • Deepest vertical pocket (preferred) < 2 cm
    • Amniotic fluid index (AFI) < 5 cm
  • Underlying placental abnormalities, e.g., placental insufficiency
  • Associated fetal complications of oligohydramnios

Oligohydramnios may be discovered incidentally on routine prenatal ultrasound imaging. ^[5][6][7]

Refer all patients to maternal-fetal medicine for further evaluation and management, which may include the following:

• Identification and management of causes of oligohydramnios and fetal complications of oligohydramnios
• Antepartum surveillance and early delivery ^[5][8]
  • No identified cause or complication (isolated oligohydramnios)
    • Antenatal surveillance 1–2 times per week ^[1]
    • Planned delivery between 36 0/7 and 37 6/7 weeks' gestation ^[8]
  • Identified cause or complication
    • Antenatal surveillance and management are individualized.
    • Associated fetal growth restriction: planned delivery between 34 0/7 and 37 6/7 weeks' gestation ^[8]
    • Immediate delivery may be indicated for severe maternal or fetal complications.
• Amnioinfusion (infusion of fluid into the amniotic cavity) may be considered to increase amniotic fluid volume. ^[2]

Management of oligohydramnios is based on gestational age, underlying cause, and associated complications. ^[5]

Planned preterm delivery is an indication for corticosteroids to induce fetal lung maturity. ^[9]

Fetal and newborn complications

• Fetal growth restriction
• Intrauterine fetal demise ^[1]
• Umbilical cord compression or, during labor and delivery, umbilical cord prolapse
• Complications of prematurity (secondary to iatrogenic preterm birth) ^[8][10]
• Any clinical features of Potter sequence

Potter sequence

• Etiology
  • Chronic placental insufficiency
  • ↓ Renal output (e.g., due to bilateral renal agenesis, ARPKD, obstruction of posterior urethral valves)
  • Chronic amniotic fluid leakage
  • See “Causes of oligohydramnios.”
• Pathophysiology: : oligohydramnios → intrauterine compression and decreased amniotic fluid ingestions → ↓ space for fetal development → internal and external deformations
• Clinical features
  • Pulmonary hypoplasia (cause of death due to severe neonatal respiratory insufficiency) ^[2]
  • Sequelae of intrauterine constraint
    • Craniofacial abnormalities (e.g., prominent epicanthal and infraorbital folds, flattened nose, receding chin, low set ears)
    • Skeletal deformities, e.g., DDH, congenital torticollis, joint contractures
  • Wrinkling of the skin

Potter babies cannot Pee.

POTTER sequence: Pulmonary hypoplasia (lethal), Oligohydramnios (origin), Twisted facies, Twisted skin, Extremity deformities, and Renal agenesis (classic form).

We list the most important complications. The selection is not exhaustive.