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Hydramnios

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References:

  1. Maternal & Child Health Nursing: Care of the childbearing & childrearing family, 8th Edition, ISBN 978-1-4963-4813-5, by JoAnne Silbert-Flagg and Adele Pillitteri (Ch. 21)

Polyhydramnios

At term, the normal volume of amniotic fluid ranges from 500 to 1000 mL. Polyhydramnios occurs when there is excess fluid of more than 2,000 mL or an amniotic fluid index above 24 cm. Polyhydramnios can cause fetal malpresentation because the additional uterine space can allow the fetus to turn to a transverse lie. It also can lead to premature rupture of the membranes from the increased pressure, which then leads to the additional risks of infection, prolapsed cord, and preterm birth.

Assessment

Amniotic Fluid Formation and Resorption

Amniotic fluid is formed by a combination of the cells of the amniotic membrane and from fetal urine. It is evacuated by being swallowed by the fetus, absorbed across the intestinal membrane into the fetal bloodstream, and transferred across the placenta.

Although polyhydramnios can occur separate from fetal involvement, accumulation of amniotic fluid suggests difficulty with the fetus’s ability to swallow or absorb, or excessive urine production. Inability to swallow occurs in infants who are anencephalic, who have tracheoesophageal fistula with stenosis, or who have intestinal obstruction. Excessive urine output occurs in the fetuses of diabetic women (hyperglycemia in the fetus causes increased urine production).

  1. The first sign of polyhydramnios may be unusually rapid enlargement of the uterus. The small parts of the fetus become difficult to palpate because the uterus is unusually tense. Auscultating the FHR can be difficult because of the depth of the increased amount of fluid surrounding the fetus.
  2. A woman may begin to notice extreme shortness of breath as the overly distended uterus pushes up against her diaphragm.
  3. She may develop lower extremity varicosities and hemorrhoids because good venous return from the lower extremities is blocked by extensive uterine pressure.
  4. The increased amount of fluid will cause increased weight gain.

Generally, an ultrasound is done to document the presence of polyhydramnios and to discover a reason for the excessive amount of fluid.

Therapeutic Management

Women with severe polyhydramnios may be admitted to a hospital for bed rest and further evaluation or may be cared for at home. Regardless of the setting, maintaining bed rest helps to increase uteroplacental circulation and reduces pressure on the cervix, which may help prevent preterm labor.

  1. Teach a woman that it is vitally important to report any sign of ruptured membranes or uterine contractions.
  2. Although not common, there is a possibility that straining to defecate could increase uterine pressure and cause a rupture of membranes. Help her, therefore, avoid constipation by encouraging her to eat a high-fiber diet. Suggest a stool softener if diet alone is ineffective.
  3. Assess vital signs as well as lower extremity edema frequently (the extremely tense uterus puts unusual pressure on both the diaphragm and the vessels of the pelvis).
  4. Amniocentesis can be performed to remove some of the extra fluid. Because amniotic fluid is replaced rapidly, however, this has to be repeated almost daily to be effective.
  5. If contractions begin, tocolysis may be necessary to prevent or halt preterm labor. Polyhydramnios may also lead to placental separation or a rupture of membranes.
  6. Excessive pressure will often still result to a preterm rupture of the membranes despite precautions set in place, followed by preterm birth. To prevent the sudden loss of fluid and the accompanying danger of a prolapsed cord during labor, membranes can be “needled” which uses a thin needle inserted vaginally to allow a slow, controlled release of fluid.
  7. Once delivered, the infant should be assessed for potential fetal causes of polyhydramnios such as an ability to swallow or a gastrointestinal blockage.

Oligohydramnios

Oligohydramnios refers to a pregnancy with less than the average amount of amniotic fluid. Because part of the volume of amniotic fluid is formed by the addition of fetal urine, this reduced amount of fluid is usually caused by a bladder or renal disorder in the fetus that is interfering with voiding. It also can occur from severe growth restriction (because of the small size, a fetus is not voiding as much as usual).

Oligohydramnios is suspected during pregnancy when the uterus fails to meet its expected growth rate. It is confirmed by ultrasound when the pockets of amniotic fluid are less than average. Infants need careful inspection at birth to rule out kidney disease and compromised lung development.

Fetal Prognosis

Because the fetus is so cramped for space, muscles are left weak at birth, lungs can fail to develop (hypoplastic lungs), possibly leading to severe difficulty breathing after birth, and distorted features of the face occur (collectively termed Potter syndrome).

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