Causes of Oligohydramnios

Fetal Causes

• Fetal asphyxial states / IUGR
• Premature rupture of fetal membranes
• Developmental anomalies of the genitourinary system
• Chromosomal abnormalities
• Congenital syndromes
• Intrauterine fetal demise

Maternal Causes

• Uteroplacental insufficiency
• Drugs

Placental Causes

• Placental abruption
• Twin - twin transfusion

Idiopathic

• Diagnostic criteria (1):
• AFI 5mm or less.
• AFI > 5mm but < 2.5^th centile.
• Exclude – premature rupture of membranes, insulin dependent diabetes, maternal hypertension or pre-eclampsia, fetal growth restriction, fetal anomalies or systemic maternal disease.
• Kreiser et.al. (2) assessed perinatal outcome in 150 low-risk pregnancies > 30 wks but complicated by isolated oligohydramnios. The outcomes of 57 pregnancies with AFI of 5mm or less were compared with 93 pregnancies with AFI > 5cm but <2.5^th centile. There were no significant differences between the pregnancies with respect to labor induction for an abnormal stress test, overall cesarean deliveries for heart rate abnormalities, overall presence of meconium and Apgar score < 7 at 5 mins. No perinatal deaths in either group. Authors conclude that outcome in low risk pregnancies with isolated oligohydramnios is good but requires antepartum monitoring 1-3 times per week.
• Conway et.al. (3) conclude that isolated oligohydramnios in the otherwise normal term pregnancy may not be a marker for fetal compromise and that induction of labor may therefore not be warranted in most cases.

REFERENCES

1. Sherer DM, Langer O. Editorial. Oligohydramnios: use and misuse in clinical management. Ultrasound Obstet Gynecol 2001;18:411-419.
2. Kreiser D, El-Sayed Y, Sorem KA et.al. Decreased amniotic fluid index in low-risk pregnancy. J Reprod Med 2001;46:743-746.
3. Conway DL, Adkins WB, Schroeder B et.al. Isolated oligohydramnios in the term pregnancy: is it a clinical entity? J Matern Fetal Med 1998;7:197-200.

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