Oligohydramnios in the Third Trimester

Contributor: Eric Dellinger, MD
Last Update: 2/24/2016

Definition:
Two objective criteria can be used to diagnose oligohydramnios:
Amniotic fluid index ≤5.0 cm1
Single deepest pocket <2.0 cm2

Comment:  Amniotic fluid index vs. Single deepest pocket.
Five trials of 3226 subjects found no superiority of one method versus another for prevention of poor perinatal outcome
including NICU admission, umbilical artery pH < 7.1, meconium, Apgar < 7 at 5 minutes, or cesarean section. Use of the AFI
resulted in increased diagnosis of oligohydramnios (RR 2.39, 95% CI 1.73 to 3.28), more induction of labor (RR 1.92; 95% CI
1.50 to 2.46) and more cesarean delivery for fetal distress (RR 1.46; 95% CI 1.08 to 1.96).6

Management:
Perform a thorough maternal history and targeted physical examination, looking for the following causes of oligohydramnios3:

• Maternal
  • Uteroplacental insufficiency (from preeclampsia, chronic hypertension, lupus, etc.)
  • Medications (ACE inhibitors, prostaglandin synthetase inhibitors, etc.)
• Placental
  • Abruption
  • Twin to twin transfusion
  • Placental thrombosis or infarction
• Fetal
  • Chromosomal abnormalities
  • Congenital abnormalities, especially urinary tract obstructions
  • Growth restriction
  • Demise
  • Post term pregnancy
  • Ruptured fetal membranes
• Idiopathic

Exclude premature rupture of membranes as a cause.
Perform a complete sonographic evaluation of the fetus, placenta, amniotic fluid, and Dopplers.
​
EGA > 37 0/7 weeks: Consider delivery (Grade 2C evidence)4
EGA < 37 0/7 weeks: Attempt to increase the amniotic fluid volume by:

1. IV hydration, usually in the hospital setting.
2. Oral hydration, if patient declines hospital admission.
3. Amnioinfusion, usually reserved for cases where improved sonographic visualization is felt to be important.
   • If the AFI normalizes, then repeat the measurement in one week.
   •  If oligohydramnios persists, then begin antepartum fetal testing protocol.
   • The decision to deliver can be individualized. Doppler values can be valuable in this setting. Isolated oligohydramnios with normal Dopplers might be more conducive to carrying to term, while abnormal Dopplers and comorbidities might suggest the need for an earlier delivery. Amniocentesis in rare cases can assist with scheduling delivery (e.g. poor dating), but in most cases is not recommended as it can be technically challenging with low fluid volumes.

References

1. Rutherford SE, Phelan JP, Smith CV, Jacobs N. The four-quadrant assessment of amniotic fluid volume: an adjunct to antepartum fetal heart rate testing. Obstet Gynecol 1987; 70:353.
2. Chamberlain, PF, Manning, FA, Morrison, I, Harman, CR, and Lange, IR. Ultrasound evaluation of amniotic fluid volume. I. The  relationship of marginal and decreased amniotic fluid volumes to perinatal outcome. Am J Obstet Gynecol. 1984; 150: 245–24.
3. Beloosesky R, Ross MG. Oligohydramnios. In: UpToDate, Lockwood CJ (Ed), UpToDate, Waltham, MA. (Accessed on November 11, 2014.)
4. Bastide A, Manning F, Harman C, Lange I, Morrison I. Ultrasound evaluation of amniotic fluid: outcome of pregnancies with severe oligohydramnios. Am J Obstet Gynecol. 1986;154(4):895.
5. Carroll BC, Bruner JP. Umbilical artery Doppler velocimetry in pregnancies complicated by oligohydramnios. J Reprod Med. 2000  Jul;45(7):562-6.
6. ​Nabhan AF, Abdelmoula YA. Amniotic fluid index versus single deepest vertical pocket as a screening test for preventing adverse pregnancy outcome. Cochrane Database of Systematic Reviews 2008, Issue 3.