Polyhydramnios Statistics

Polyhydramnios is a rare condition that complicates about 1% of all pregnancies. This page breaks down many of the known statistics surrounding it.

Table of Contents

Statistics

Severity of Polyhydramnios

  • 65-70% – mild (SDP 8-11 cm  or AFI 24-30 cm)
  • 20% – moderate (SDP 12-15 cm or AFI 30.1-35 cm)
  • 10-15% – severe (SDP 16 cm + or AFI 35.1 cm +)

Frequency of Polyhydramnios

According to a 2018 OB-GYN Workforce Study in the United States, “nationally, there are – on average – 100 births per OB-GYN annually.”

That means, that the average OB-GYN in the United States sees 

  • 1 mild case of Polyhydramnios every year
  • 1 moderate case of Polyhydramnios every 4 years
  • 1 severe case of Polyhydramnios every 6 years
To give them extra credit… when the overall frequency of Polyhydramnios is closer to 2%, then the average OB-GYN in the United States sees
  • 2 mild cases of Polyhydramnios every year
  • 1 moderate case of Polyhydramnios every other year
  • 1 severe case of Polyhydramnios every 3 years

How Common is Idiopathic Polyhydramnios?

Idiopathic refers to “any disease that is of uncertain or unknown origin.”

 

  • Of mild cases, 83% have an unknown origin
  • Of moderate/severe cases 9% have an unknown origin
  • 57-60% of all cases of Polyhydramnios are considered idiopathic at the time of delivery
  • Mild cases are much more likely to be idiopathic and result in uncomplicated deliveries of healthy babies
  • The more severe the Polyhydramnios is the more likely a woman is to experience complications during delivery and with her baby.   

What Causes Polyhydramnios?

Only 40-43% of cases of polyhydramnios have an identifiable cause before delivery. Out of those cases, these are the statistics for the origin:

  • 45% – genetic anomaly (~18% of all Polyhydramnios cases)
  • 25.5% – other conditions, such as infection or blood incompatibility (~10% of all Polyhydramnios cases)
  • 11% – fetal anemia (~4% of all Polyhydramnios cases)
  • 10% – complications of multiple pregnancies (~4% of all Polyhydramnios cases)
  • 8.5% – maternal diabetes (~3% of all Polyhydramnios cases)
These statistics come from new research in a small study that suggests the rate of maternal diabetes as one of the causes of Polyhydramnios is actually significantly less than previously thoughtThis research also concluded that maternal diabetes as the cause of Polyhydramnios was almost exclusively found in only mild cases of Polyhydramnios. 

Rates of Adverse Outcomes in Labor and Delivery with Polyhydramnios

  • Rate of induction is 7.9% (vs. normal pregnancies: 4.8%)
  • Rate of c-section is 12.1% (vs. normal pregnancies: 5.1%)
  • Rate of placental abruption is 0.9% (vs. normal pregnancies: 0.2%)
  • Rate of abnormal fetal heart rate is 7% (vs. normal pregnancies: 3.2%)
  • Rate of prolonged first stage of delivery is 6% (vs. normal pregnancies: 1.4%)
  • Rate of shoulder dystocia is 1.9% (vs. normal pregnancies: 0.3%)
  • Rate of Respiratory Distress Syndrome is 0.5% (vs. normal pregnancies: 0.03%)
  • 35-55% of c-section deliveries in Polyhydramnios are due to failure to progress

Umbilical Cord Prolapse (UCP) with Polyhydramnios

Cord prolapse occurs in roughly 0.1-0.3% (3 out of every 1000) of all deliveries, usually due to malpresentation, SROM, fetal weight <2500 grams, polyhydramnios, or delivering multiples. Roughly 65% of these cases occur in women who have had at least one previous delivery.
 
According to a 2016 nationwide study in Japan, patients who experienced UCP were 
  • 3.57 times more likely to be pregnant with multiples
  • 4.67 times more likely to have a non-vertex presentation
  • 2.28 times more likely to have preterm labor
  • 3.84 times more likely to have PROM
  • 12.31 times more likely to have a prolapsed amniotic bag
  • 2.89 times more likely to have Polyhydramnios
  • 2.26 times more likely to have a birth weight <2500 grams
 
 Here’s a different way to look at it:
  • 9% of all pregnancies have SROM, 1.9% of these experience UCP
  • 4.3% of all deliveries are breech, 2.5-7.5% of these experience UCP
  • 4.4% of all deliveries are transverse, 3.8-4.6% of these experience UCP
  • 15.3% of all deliveries have a birthweight <2500 grams; 0.9-2.4% of these experience UCP
 
Mortality rate of UCP:
  • 3% when UCP occurs in the hospital
  • 44% when UCP occurs outside of the hospital

Other Statistics to Know about Polyhydramnios

  • Polyhydramnios increases the risk of late fetal demise
  • Polyhydramnios babies have a higher rate of NICU admittance than the normal population
  • 9% of cases end up identifying a cause  during the immediate neonatal period
  • 28% of cases end up identifying the cause within the first year of the baby’s life

FAQs

FAQs

Read Next

Questions for Your Doctor – If you’ve been diagnosed with Polyhydramnios, you probably have a lot of questions. Use our guide to help you get the right ones answered.

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