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Ron Beloosesky, MD
Michael G Ross, MD, MPH
Section Editors
Lynn L Simpson, MD
Deborah Levine, MD
Deputy Editor
Vanessa A Barss, MD, FACOG


Polyhydramnios (also known as hydramnios) refers to an excessive volume of amniotic fluid. It has been associated with an increased risk of various adverse pregnancy outcomes, including preterm birth, placental abruption, and fetal anomalies [1-3]. Polyhydramnios should be suspected clinically when uterine size is large for gestational age. The diagnosis is made prenatally by ultrasound examination using a noninvasive qualitative or quantitative approach. (See "Assessment of amniotic fluid volume".)


The incidence of polyhydramnios in a general obstetric population generally ranges from 1 to 2 percent [4-8]. Reported rates are influenced by variations in diagnostic criteria, the population studied (low or high risk), the subjective volume of fluid where polyhydramnios is diagnosed (eg, mild, moderate, or severe), and the gestational age (preterm, term, or postterm) at examination. In one series of 93,332 singleton pregnancies delivering at a single hospital from 1991 to 1997, polyhydramnios was diagnosed during antepartum sonography in 708 pregnancies (0.7 percent of deliveries); mild, moderate, and severe disease occurred in 66, 22, and 12 percent of cases, respectively [5].


Any condition that results in even a relatively minor increase in daily fetal urine production or decrease in fetal swallowing can result in a marked increase in amniotic fluid volume (AFV) [9-11]. The volume of amniotic fluid reflects the balance between fluid production and movement of fluid out of the amniotic sac; the regulation of this process is incompletely understood (see "Physiology of amniotic fluid volume regulation"). In late gestation, the primary sources of amniotic fluid production are fetal urination and secretion of lung fluid; oral and nasal secretions make minimal contributions. The main routes of amniotic fluid removal are fetal swallowing and absorption via the intramembranous pathway.


Polyhydramnios may be idiopathic or associated with a variety of fetal disorders, including:

Fetal structural anomaly/anomalies

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Literature review current through: Oct 2017. | This topic last updated: Mar 03, 2017.
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