Practical obstetrics info for your women's healthcare practice

Polyhydramnios – Possible Causes and Next Steps

WHAT IS IT?

The term polyhydramnios, also known as hydramnios, refers to an excessive amount of amniotic fluid. The primary sources of amniotic fluid are fetal urine production, fetal lung fluid and fetal oral and nasal secretions. The main routes of amniotic fluid removal are fetal swallowing and absorption via the intramembranous pathway.

Incidence and Causes

  • The overall incidence is 0.2-2.0 % of pregnancies
    • More common in twins, likely due to complications of monochorionic placentation
  • Idiopathic polyhydramnios will occur in approximately 1% of pregnancies
  • Causes of polyhydramnios are many and account for varying percentages of cases:
    • Idiopathic polyhydramnios (50-60%)
    • Congenital anomalies and genetic disorders (8-45%)
    • Maternal diabetes (5-26%)
    • Multiple gestation (8-10%)
    • Fetal anemia (1-11%)

Measurement

  • Two commonly used sonographic measurements that suggest an increased volume of amniotic fluid include (Grade 2C)
    • Amniotic fluid index (AFI) of ≥24 cm based on a total measurement of 4 different quadrants

OR

    • A single deepest pocket (SDP) of ≥8 cm, measured by holding the ultrasound transducer perpendicular to the floor in the sagittal plane
  • SMFM states in the consult series (see ‘Learn More – Best Practices’ below) that polyhydramnios can be defined by either AFI or SDP using the above parameters, but also recommends use of SDP in the 3rd trimester (see ‘Related ObG Topics’ below)
  • ACOG states that “best available evidence supports using the deepest vertical pocket method of measurement because it leads to fewer interventions with no increase in poor perinatal outcomes compared with use of the AFI”
  • Severity
    • Mild AFI: 24.0-29.9 cm or SDP 8-11 cm
    • Moderate AFI: 30.0-34.0 cm or SDP 12-15 cm
    • Severe AFI: ≥35 cm or SDP ≥16 cm
  • Recommended AFI technique
    •  Amniotic fluid pocket must be ≥1 cm wide
    • Measured pocket(s) should not contain fetal parts or loops of umbilical cord
      • Color Doppler can be used to identify cord
  • Increasing severity of polyhydramnios correlates with an increased risk of perinatal mortality and congenital abnormalities

KEY POINTS:

  • Idiopathic polyhydramnios is a diagnosis of exclusion
    • At diagnosis, refer for anatomic survey and work up to rule out alloimmunization, congenital infection, diabetes and other causes
    • Alert patient that even with a full and thorough ‘negative’ work-up, and underlying cause may be identified following delivery
  • Assess fetal growth
    • Association between macrosomia and polyhydramnios
    • IUGR may be related to single gene or chromosomal anomaly such trisomy 13 or 18
  • Rescreening for diabetes (data limited)
    • Consider if polyhydramnios identified in the 3rd trimester or more than 1 month since diabetes screen
  • Severe polyhydramnios
    • Especially if early in pregnancy, should be considered concerning and generate a referral to high-risk and genetic specialists
      • Detailed medical and family history is required
    • SMFM recommends delivery at a specialized, tertiary care unit (GRADE 1C)

Antepartum Management

  • Amniocentesis
    • No data to support amniocentesis specifically for isolated polyhydramnios
    • However, additional findings such as altered growth or movement may involve offering invasive testing to determine underlying cause
    • Note: ACOG/SMFM guidelines state that invasive testing should be made available to all women
  • Amnioreduction
    • SMFM recommends against amnioreduction except in the presence of severe polyhydramnios and (GRADE 1C)
      • Severe maternal discomfort and/or
      • Dyspnea
  • Indomethacin
    • Not recommended for the sole purpose of decreasing amniotic fluid (GRADE 1B)
    • Increased neonatal risks including
      • Decreased neonatal (preterm) urine output and elevated
        serum creatinine
      • Intraventricular hemorrhage | Periventricular leukomalacia | Necrotizing enterocolitis
  • Serial growth scans
    • SMFM suggests that “antenatal fetal surveillance is not required for the sole indication of mild idiopathic polyhydramnios” (GRADE 2C)
  • Induction vs Spontaneous Labor (GRADE 1C)
    • SMFM recommends that labor be allowed to occur spontaneously in the case of mild idiopathic polyhydramnios
    • Do not induce <39 weeks gestation without indication
    • Mode of delivery based on obstetrical indications
  • Timing of delivery (mild, idiopathic)
    • 39w0d – 40w6d

Intrapartum Management

  • Data to support higher risk for dysfunctional labor and cesarean section
  • Determine fetal presenting part on admission to L&D
    • Clinical or ultrasound
    • External cephalic version for nonvertex presentation may be considered if patient meets criteria and no contraindications
  • Amniotomy
    • “Controlled” amniotomy for moderate or severe polyhdramnios has been suggested, to be performed in the OR using spinal or pudendal block
    • Note: No evidence that this approach is advantageous
  • PPH
    • Increased risk for PPH
    • Uterotonics should be available in the delivery room
  • Risk of structural anomalies/genetic syndromes
    • Even if no antenatal diagnosis available, pediatric support should be available for any degree of polyhydramnios

Learn More – Primary Sources:

SMFM Consult Series #46 : Evaluation and Management of Polyhydramnios

ACOG/SMFM Committee Opinion 831: Medically Indicated Late-Preterm and Early-Term Deliveries

ACOG Practice Bulletin No. 175: Ultrasonography in Pregnancy

Single Deepest Vertical Pocket or Amniotic Fluid Index as Evaluation Test for Predicting Adverse Pregnancy Outcome (SAFE Trial): A Multicenter, Open-label, Randomized Controlled Trial

Locate a genetic counselor or genetics services:

Genetic Services Locator-ACMG

Genetic Services Locator-NSGC

Genetic Services Locator-CAGC

Locate a Maternal Fetal Medicine Specialist

Maternal Fetal Medicine Specialist Locator-SMFM