Oligohydramnios / Polyhydramnios

Snapshot

• A 26-year-old G2P1 woman presents to her regular obstetrics checkup at 12 weeks gestation. She had been tolerating the pregnancy without issue. Her first pregnancy did not have any complications, and she had delivered a boy at 39 weeks via spontaneous vaginal delivery. On ultrasound, she is noted to have oligohydramnios. Further evaluation shows that the fetus has polycystic kidneys. (Oligohydramnios)

Introduction

• Overview
  • amniotic fluid is essential for fetal growth and development, protecting the fetus from trauma and infection, and aids the development of fetal lungs
  • polyhydramnios
    • abnormally high volume of amniotic fluid
  • oligohydramnios
    • abnormally low volume of amniotic fluid

Overview of Polyhydramnios vs Oligohydramnios
	Polyhydramnios	Oligohydramnios
Epidemiology	1% of all pregnanices	11% of all pregnanices
Etiology	Congenital anomaly (most common)fetal gastrointestinal tract blockage (esophageal atresia and other intestinal atresia) Twin-twin transfusion syndromeMaternal diabetes	Rupture of membranes  (most common)Fetal urinary tract blockage (polycystic kidneys, posterior urethral valves, and renal agenesis) Maternal substance abuse
Prognosis	Usually associated with good prognosis	Mortality rate is high, particularly if diagnosed in the first trimesterOligohydramnios can increase the fetal risk for chest wall fixation and pulmonary hypoplasia

• Prognosis
  • polyhydramnios and oligohydramnios on their own are associated with good prognosis
• however, depending on the etiology, such as renal agenesis where mortality is 100%, prognosis varies

Presentation

• Symptoms
  • often asymptomatic
  • may have abdominal discomfort if severe
• Physical exam
• large uterus (polyhydramnios)

Imaging

• Ultrasound
  • indication
    • all patients
  • findings
    • can assess for amniotic fluid index (AFI)
      • calculated by dividing the abdomen into four quadrants and using the largest vertical pocket of fluid to estimate the total volume
      • polyhydramnios
        • AFI > 24 cm  
      • oligohydramnios
        • AFI < 7 cm 
    • fetal structure survey
• may also visualize any congenital abnormalities

Differential

• Twin-twin transfusion syndrome 
  • key distinguishing factor
• monozygotic twin pregnancy with anastomotic vessel shunting from one fetus to another

Treatment

• Medical
  • prostaglandin synthetase inhibitors
    • indication
      • to reduce amniotic fluid volume
      • maternal discomfort
      • preterm labor
    • modalities
      • indomethacin
    • complications
      • closure of ductus arteriosus
        • monitor with fetal echocardiograph with Doppler
        • closure resolves within 24 hours of discontinuing indomethacin
• Surgical
  • transabdominal amniocentesis
    • indication
      • polyhydramnios
        • maternal discomfort
        • preterm labor
    • complications
      • placental abruption
      • fetal maternal hemorrhage
      • fetal pneumothorax
      • risk of infection
  • transcervical amnioinfusion
    • indications
      • oligohydramnios
        • to improve detection of fetal structural anomalies
        • to prevent serious complications if severe
      • short-term improvement
    • complications
      • amniotic fluid embolism
      • maternal respiratory distress
  • delivery at 37-38 weeks
    • indications
• idiopathic olighydramnios

Complications

• Oligohydramnios
  • chest wall fixation
  • pulmonary hypoplasia