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Polyhydramnios - Important Note about Amniotic Fluid

Amniotic fluid [AF] can be detected from the very beginning of formation of the gestational sac (extra-embryonic coelom or chorionic cavity). This firstly water-like fluid originates from the maternal plasma, and passes through the fetal membranes by osmotic and hydrostatic forces. As the placental and fetal vessels develop, the fluid passes through the fetal tissue, as the exsudatum of the skin. After the 20th-25th week of pregnancy when the keratinization of skin occurs, the quantity of amniotic fluid begins to depend on the factors that comprise the circulation of AF.

The volume of amniotic fluid is positively correlated with the growth of fetus.

Amniotic fluid is inhaled and exhaled by the foetus. It is essential that fluid be breathed into the lungs in order for them to develop normally. Swallowed amniotic fluid also creates urine and contributes to the formation of meconium. Amniotic fluid protects the developing baby by cushioning against blows to the mother's abdomen, allowing for easier fetal movement and promoting muscular/skeletal development. Amniotic fluid swallowed by fetus help in the formation of gastrointestinal tract.

Polyhydramnios is a medical condition describing an excess of amniotic fluid in the amniotic sac. It is seen in about 1% of pregnancies. It is typically diagnosed when the amniotic fluid index (AFI) is greater than 24 cm. There are two clinical varieties of polyhydramnios:
  • Chronic polyhydramnios where excess amniotic fluid accumulates gradually
  • Acute polyhydramnios where excess amniotic fluid collects rapidly
In most cases, the exact cause cannot be identified. A single case may have one or more causes, including intrauterine infection (TORCH), rh-isoimmunisation, or chorioangioma of the placenta. In a multiple gestation pregnancy, the cause of polyhydramnios usually is twin-to-twin transfusion syndrome. Maternal causes include cardiac problems, kidney problems, and maternal diabetes mellitus, which causes fetal hyperglycemia and resulting polyuria (fetal urine is a major source of amniotic fluid).

There are several pathologic conditions that can predispose a pregnancy to polyhydramnios. These include a maternal history of diabetes mellitus, Rh incompatibility between the fetus and mother, intrauterine infection, and multiple pregnancies.

During the pregnancy, certain clinical signs may suggest polyhydramnios. In the mother, the physician may observe increased abdominal size out of proportion for her weight gain and gestation age, uterine size that outpaces gestational age, shiny skin with stria (seen mostly in severe polyhydramnios), dyspnea, and chest heaviness. When examining the fetus, faint fetal heart sounds are also an important clinical sign of this condition.

Treatment of Polyhydramnios
  • Mild asymptomatic polyhydramnios is managed expectantly. For a woman with symptomatic polyhydramnios may need hospital admission. Antacids may be prescribed to relieve heartburn and nausea.
  • No data support dietary restriction of salt and fluid.
  • In some cases, amnioreduction, also known as therapeutic amniocentesis, has been used in response to polyhydramnios.
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