Polyhydramnios


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Definition

Polyhydramnios is too much amniotic fluid surrounding an unborn infant.


Considerations

Amniotic fluid is a clear, slightly yellowish liquid that surrounds the unborn baby (fetus) during pregnancy. The amniotic fluid constantly moves as the baby swallows and breathes in the fluid, and then releases it through urine.

While in the womb, the baby floats in the amniotic fluid. Amniotic fluid surrounds and cushions the infant throughout pregnancy. The amount of amniotic fluid is greatest at around 34 weeks of pregnancy.

The amniotic fluid helps:

  • The developing baby move in the womb, which allows for proper bone growth
  • The lungs to develop properly
  • Keep a relatively constant temperature around the baby, protecting from heat loss
  • Protect the baby from outside injury by cushioning sudden blows or movements

Common Causes

Polyhydramnios can occur if the developing baby does not swallow and absorb amniotic fluid in normal amounts. This can happen if the baby has certain health problems, including:

  • Gastrointestinal disorders, such as duodenal atresia, esophageal atresia, gastroschisis, and diaphragmatic hernia
  • Brain and nervous system problems, such as anencephaly and myotonic dystrophy
  • Achondroplasia
  • Beckwith-Wiedemann syndrome

It can also happen if the mom has poorly controlled diabetes.

Polyhydramnios may also be due to increased fluid production, which occurs with:

  • Certain lung disorders in the baby
  • Multiple pregnancy (for example, twins or triplets)
  • Hydrops fetalis in the baby

Sometimes, no specific cause for polyhydramnios is found.


References

Carlo WA. High-risk pregnancies. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 89.

Cunningham FG, Leveno KJ, Bloom SL, et al. Disorders of amnionic fluid volume. In: Cunningham FG, Leveno KL, Bloom SL, et al, eds. Williams Obstetrics. 23rd ed. New York, NY: McGraw-Hill; 2010:chap 21.

Gilbert WM. Amniotic fluid disorders. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Churchill Livingstone; 2007:chap 31.


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Review Date: 9/19/2011
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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