Bruce J. Schlomer, MD
Laurence S. Baskin, MD, FACS, FAAP
BASICS
DESCRIPTION
• Oligohydramnios is defined as an abnormally low amniotic fluid (AF) volume:
– Associated with increased fet al morbidity and mortality
• Polyhydramnios is defined as an abnormally high AF volume:
– Up to 20% of neonates will have a congenital anomaly
– Associated with increase in aneuploidy, congenital malformations, preterm delivery, and perinatal death
• These conditions are diagnosed using prenatal US with strict criterion described below
EPIDEMIOLOGY
Incidence
• Oligohydramnios in 3–5% of pregnancies (1)
• Polyhydramnios in 1–3% of pregnancies (1)
• Usually discovered in 2nd trimester with 40% normal by term
Prevalence
N/A
RISK FACTORS
• Oligohydramnios:
– Rupture of membranes
– Some medications (eg, NSAIDs)
– Maternal HTN
– Maternal autoimmune disorders
• Polyhydramnios:
– Maternal diabetes
– Drug abuse
Genetics
Several genetic syndromes are associated with oligohydramnios or polyhydramnios
PATHOPHYSIOLOGY
• After 22–23 wk, most of AF is fet al urine
• Late in gestation AF averages ∼700–800 mL
• Oligo- and polyhydramnios are due to an imbalance in the production and removal of amniotic fluid
• Production of amniotic fluid (2)
– 600–1,200 mL/d fet al urine
– 60–100 mL/kg/d tracheal secretions
• Removal of amniotic fluid (2)
– 200–1,500 mL/d fet al swallowing
– 200–500 mL/d removed across fet al placenta into fet al blood stream (intramembranous pathway)
• Oligohydramnios causes
– PROMs
Iatrogenic: Amniocentesis
Spontaneous/idiopathic
– Decreased fet al urine production
Prerenal: Placental insufficiency, umbilical cord compression, fet al demise, maternal hypotension or severe dehydration, chronic maternal HTN, autoimmune disorders, drugs (NSAIDs, ACE inhibitors)
Intrarenal: Renal dysplasia, renal agenesis
Obstructive: Posterior urethral valves (PUVs), prune belly syndrome, urethral atresia, bilateral ureteropelvic junction obstruction (UPJO), bilateral ureteral obstruction, bilateral ectopic ureters
• Effects of oligohydramnios
– Pulmonary hypoplasia: Correlated with fet al outcome and main cause of fet al death
– Intrauterine growth restriction
– Potter facies with severe oligohydramnios
– Better outcome if presents in 3rd trimester vs. 2nd trimester (3)
– Better outcome if cause is PROM vs. congenital anomaly (3)
• Causes of polyhydramnios
– Idiopathic: ∼60%
Better outcomes
– Maternal causes: ∼15%
Maternal diabetes
Infections: Syphilis, rubella, MV, toxoplasmosis, parvovirus, Rh isoimmunization
Drug abuse: Polyhydramnios in ∼25–30% of drug-addicted women. Leads to decreased neurologic function of fetus and decreased swallowing
– Fet al causes:
Reduced fet al swallowing: Maternal drug use, fet al neurologic anomalies, aneuploidy
GI anomalies: T-E fistula, choanal atresia, facial cleft, esophageal atresia, imperforate anus
Cardiac failure with diuresis
Karyotype anomalies
ASSOCIATED CONDITIONS
• Oligohydramnios:
– Rupture of membranes
– Placental insufficiency
– Chronic maternal HTN
– Postdate gestation
– Multicystic dysplastic kidney or prune-belly syndrome
– Severe cardiac disease
– Pulmonary hypoplasia, limb abnormalities
– Potter syndrome:
Characteristic appearance usually due to bilateral renal agenesis, obstructive uropathy, renal hypoplasia, autosomal recessive polycystic kidney disease
Less severe form referred to as Potter sequence
• Polyhydramnios
– Anencephaly
– Neural tube defects
– GI obstruction (esophageal atresia, duodenal atresia)
– Multiple gestation
– Nonimmune hydrops fet alis
– Maternal diabetes
GENERAL PREVENTION
• Oligohydramnios
– Avoid known medications (NSAIDs, etc.)
– Avoid unneeded amniocentesis
– Avoid maternal dehydration
• Polyhydramnios
– Control of maternal diabetes
– Prevention of infections transmittable from mother to fetus
– Avoid drug abuse
DIAGNOSIS
HISTORY
• Polyhydramnios:
– Increased maternal weight
– Maternal drug use
– Maternal infectious exposure
• Oligohydramnios:
– Poor weight gain
– Medication history
PHYSICAL EXAM
• Polyhydramnios: Increased maternal fundal height
• Oligohydramnios: Decreased maternal fundal height
• Enlarged newborn urinary bladder due to obstruction
• Potters facies:
– Characteristic of bilateral renal agenesis and other severe renal malformations
– Ocular hypertelorism, low-set ears, receding chin, flattening of the nose
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Polyhydramnios:
– Maternal testing for glucose, autoantibodies, TORCH screen, parvovirus, fet al karyotype
• Oligohydramnios:
– General: Fet al karyotype, pulmonary maturity, maternal autoantibodies (lupus, anticardiolipin, antinuclear)
– Renal: Fet al urinary electrolytes
– Better outcome associated with Na <100 mmol/L, Cl <90 mmol/L, and osm <210 mmol/L
– Serial measurements may have better prognostic value
– May also measure β2-microglobulin, α-microglobulin, and retinal-binding protein
Imaging
• US measurements of AF volumes are very operator-dependent and very variable (4)
• No perfect means to determine actual volume, but several surrogate markers are used:
– Maximum vertical pocket: Polyhydramnios >8 cm, oligohydramnios <1 cm
– AFI: Sum of largest volumes from each of 4 placental quadrants:
Oligohydramnios: <5 cm, polyhydramnios >25 cm
• Fet al MRI increasingly used for better anatomic detail
Diagnostic Procedures/Surgery
• Polyhydramnios
– Remove excess fluid
• Oligohydramnios:
– Amnioinfusion: Especially for premature PROM
Pathologic Findings
• Depends on cause (see pathophysiology)
• Renal dysplasia common finding in oligohydramnios
DIFFERENTIAL DIAGNOSIS
• Oligohydramnios
– Premature rupture of membranes (PROM)
Iatrogenic: Amniocentesis
Spontaneous/idiopathic
– Decreased fet al urine production
Prerenal: Placental insufficiency, umbilical cord compression, fet al demise, maternal hypotension or severe dehydration, chronic maternal HTN, autoimmune disorders, drugs (NSAIDs, ACE inhibitors)
Intrarenal: Renal dysplasia, renal agenesis
Obstructive: PUVs, prune belly syndrome, urethral atresia, bilateral UPJO, bilateral ureteral obstruction, bilateral ectopic ureters
– Prolonged gestation can lead to oligohydramnios late in the pregnancy
• Polyhydramnios
– Idiopathic: ∼60%
Better outcomes
– Maternal causes: ∼15%
Maternal diabetes
Infections: Syphilis, rubella, MV, toxoplasmosis, parvovirus, Rh isoimmunization
Drug abuse: Polyhydramnios in ∼25–30% of drug-addicted women. Leads to decreased neurologic function of fetus and decreased swallowing
Placental chorioangioma or arteriovenous fistula
– Fet al causes:
Reduced fet al swallowing: Maternal drug use, anencephaly, neural tube defects, muscular dystrophy syndromes, aneuploidy
GI anomalies: T-E fistula, choanal atresia, facial cleft, esophageal atresia, imperforate anus, gastroschisis, duodenal atresia/stenosis, diaphragmatic hernia
Cardiac failure: Congestive heart failure, severe anemia
Karyotype anomalies: Trisomy 21, etc.
Hydrops fet alis: Rh disease, severe anemia, infections in mother (eg, parvovirus, CMV), twin–twin transfusion syndrome, maternal hyperparathyroidism, disorders of glycosylation
Other: Sacrococcygeal teratoma, skelet al dysplasias, thoracic/mediastinal masses
TREATMENT
GENERAL MEASURES
• Polyhydramnios:
– US every 3–4 wk
– Follow pregnancy to 38 wk
– Monitor for uterine hemorrhage
• Oligohydramnios:
– US every 3–4 wk for fet al viability and BPP
– Consider early delivery with steroids for pulmonary development
– Newborn needs intensive care and urologic assessment
MEDICATION
First Line
• Maternal indomethacin has been used in cases of polyhydramnios
• Surfactant for the neonate with severe oligohydramnios and pulmonary hypoplasia
Second Line
None
SURGERY/OTHER PROCEDURES
In utero vesicoamniotic shunt in select cases of oligohydramnios due to bladder outlet obstruction
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
Amnioinfusion of isotonic sodium chloride solution in the 2nd trimester may benefit some patients with oligohydramnios
Complementary & Alternative Therapies
N/A
ONGOING CARE
PROGNOSIS
• Polyhydramnios:
– If idiopathic, the prognosis is usually good
• Oligohydramnios:
– With renal agenesis, mortality rate is 100%
– Fet al outcomes correlated to degree of pulmonary hypoplasia
– Mild forms of obstructive uropathy may cause renal insufficiency
– Better prognosis with presentation in 3rd vs. 2nd trimester (3)
– Better prognosis with PROM as cause vs. congenital anomalies (3)
COMPLICATIONS
• Polyhydramnios can cause increased preterm labor
• Oligohydramnios can cause fet al distress before or during labor and severe respiratory distress and pneumothorax due to pulmonary hypoplasia
FOLLOW-UP
Patient Monitoring
Close monitoring by prenatal sonography
Patient Resources
• www.americanpregnancy.org
• www.acog.org/For_Patients
REFERENCES
1. Volante E, Gramellini D, Moretti S, et al. Alteration of the amniotic fluid and neonatal outcome. Acta Bio Med. 2004;75:71–75.
2. Sherer DM. A review of amniotic fluid dynamics and the enigma of isolated oligohydramnios. Am J Perinatol. 2002;19:253–266.
3. Shipp TD, Bromley B, Pauker S, et al. Outcome of singleton pregnancies with severe oligohydramnios in the second and third trimesters. Ultrasound Obstet Gynecol. 2996;7:108–113.
4. Harman CR. Amniotic fluid abnormalities. Semin Perinatol. 2008;32:288–294.
ADDITIONAL READING
N/A
See Also (Topic, Algorithm, Media)
• Polyhydramnios/Oligohydramnios Image 
• Posterior Urethral Valves
• Potter Syndrome/Potter Facies
CODES
ICD9
• 657.00 Polyhydramnios, unspecified as to episode of care or not applicable
• 658.00 Oligohydramnios, unspecified as to episode of care or not applicable
• 761.2 Oligohydramnios affecting fetus or newborn
ICD10
• O40.9XX0 Polyhydramnios, unspecified trimester, not applicable or unspecified
• O41.00X0 Oligohydramnios, unspecified trimester, not applicable or unspecified
• P01.2 Newborn (suspected to be) affected by oligohydramnios
CLINICAL/SURGICAL PEARLS
• If anmiotic fluid (AF) levels are normal, the fetus is very likely to have adequate urine production even with bilateral hydronephrosis.
• In utero intervention with vesicoamniotic shunt is controversial.
• Idiopathic polyhydramnios has good outcomes.