Polyhydramnios is the presence of excessive amniotic fluid surrounding the unborn infant.
Amniotic fluid is a clear, slightly yellowish liquid that surrounds the unborn baby (fetus) during pregnancy. It is contained in the amniotic sac.
While in the womb, the baby floats in the amniotic fluid. Amniotic fluid surrounds and cushions the infant throughout development. The amount of amniotic fluid is greatest at around 34 weeks into the pregnancy (gestation).
The amniotic fluid constantly moves (circulates) as the baby swallows and "inhales" the fluid, and then releases or "exhales" the fluid through urine.
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
Polyhydramnios can occur if the fetus does not swallow and absorb amniotic fluid in normal amounts. This can happen due to:
Polyhydramnios may also be related to increased fluid production, which occurs with:
- Certain fetal lung disorders
- Multiple gestation (for example, twins or triplets)
- Hydrops fetalis
Sometimes, no specific cause for polyhydramnios is found.
What to expect at your health care provider's office
This condition is discovered during pregnancy. You may have noticed that your belly is getting large very quickly. You doctor or nurse measures the size of your uterus at every visit.
If your uterus is growing faster than expected, or it is larger than normal for your baby's gestational age, the doctor or nurse may:
- Have you come back sooner than normal to re-measure
- Perform an ultrasound
If the health care provider finds a fetal abnormality (birth defect), you may need an amniocentesis to test for a genetic defect.
Women with polyhydramnios are also more likely to go into labor early. Mild polyhydramnios that shows up in the later part of pregnancy does not often cause serious problems. More severe polyhydramnios may be treated with medications or by having extra fluid removed.
The baby will be delivered in a hospital with specialists who can provide immediate evaluation and treatment.
Stoll BJ. High-risk pregnancies. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 95.
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.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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