Polyhydramnios

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Reading:  SMFM Consult Series: #46: Evaluation and management of polyhydramnios 

What is polyhydramnios? 

  • Definition 

    • Abnormal increase in amniotic fluid volume 

    • Using ultrasonography, defined: 

      • Single deepest vertical pocket (DVP) of fluid >/= 8 cm or 

      • Amniotic fluid index (AFI) >/= 24 cm 

  • Prevalence: can complicate 1-2% of singleton gestations, but it is more common in twin gestations, primarily due to complications of monochorionic placentation 

  • Degree of polyhydramnios 

    • AFI of 24.0-29.9 cm or DVP 8-11 cm = mild (65-70% of cases) 

    • AFI of 30.0-34.9 cm or DVP of 12-15 cm = moderate (20% of cases) 

    • AFI of >/= 35 cm or DVP >/16 cm = severe (<15%)

What causes polyhydramnios, and how do we counsel patients? 

  • Most cases are mild and idiopathic 

  • When etiology is identified, most commonly due to fetal anomaly or maternal diabetes

    • Most anomalies have to do with swallowing issues 

      • GI obstruction: ie. duodenal atresia, TE fistula, thoracic mass, diaphragmatic hernia  

      • Neuro-muscular: Myotonic dystrophy, arthrogryposis, intracranial anatomy 

      • Craniofacial: cleft lip/palate, micrognathia, neck mass  

    •  Fewer due to excess urine production 

      • Renal/urinary - UPJ obstruction, mesoblastic nephroma, Bartter syndrome 

      • Cardiac (basically lesions that lead to high output cardiac failure as well): cardiac structural anomaly, tachyarrhythmia, sacrococcygeal teratoma, chorioangioma 

      • Osmotic diuresis/Other: maternal diabetes, hydrops, idiopathic 

  • What evaluations should be done? 

    • Fetal growth

    • Fetal cardiac anatomy 

    • Placenta for presence of large chorioangiomas 

    • Fetal movement to assess neurological function 

    • Position of hands/feet ot rule out arthrogryposis syndromes 

    • Presence and size of fetal stomach to r/o tracheoesophageal fistula or esophageal atresia 

    • Anatomy of fetal face/palate 

    • Positioning and appearance of fetal neck to r/o obstructing mass 

    • Fetal kidney to assess for UPJ obstruction 

    • Lower spine and pelvis for evidence of sacrococcygeal teratoma 

  • How worried should the patient be? 

    • Most mild polyhydramnios is idiopathic or due to T2DM, and only 6-10% risk of fetal anomaly, with 1% of neonatal abnormality 

    • However, with severe poly, there is increased risk of fetal anomaly to as high as 20-40% and even risk of neonatal abnormality of 10% 

    • Therefore, those with severe poly should deliver at tertiary care center due to possibility for fetal anomaly

Table describing outcomes of polyhydramnios based on severity

How do we manage polyhydramnios in pregnancy? 

  • Treatment 

    • If the poly is severe enough to cause maternal respiratory compromise, significant discomfort, or preterm labor → this can have underlying etiology 

    • In cases of severe poly that results in maternal respiratory compromise or other discomfort, then amnioreduction can be done 

      • However, the polyhydramnios will usually recur 

    • Indomethacin can decrease fetal urine output 

      • There have been studies looking at women who took indomethacin after amnioreduction to try and decrease reaccumulation and re-amnio 

      • However, preterm infants exposed to indomethacin in utero have decreased neonatal urine output and also elevated serum creatinines 

      • Therefore, indomethacin should not be used for sole purpose of decreasing amniotic fluid in the setting of poly 

  • Antepartum management 

    • Many studies have shown that idiopathic poly has been associated with infant birth weight >4000g in 15-30% of cases 

    • Reports of whether perinatal mortality is increased with idiopathic poly have been inconsistent 

      • Currently recommendation from SMFM is that antenatal fetal surveillance is not required for the sole indication of mild idiopathic poly 

      • Similarly, recommendation is that labor should be allowed to occur spontaneously at term for women with mild idiopathic poly, and that induction, if planned, should not occur at <39 weeks of gestation in the absence of other indications 

      • Most of delivery should be determined based on usual obstetric indications