Too Much Fluid In The Amniotic Sac

Pregnancy Guidelines

picture of pregnant woman with polyhydramnios
Draining fluid by amniocenteses



What Is Polyhydramnios?
What Causes It?
Symptoms And Clinical Signs
How Is It Diagnosed?
What Complications Can It Cause?
How Is It Treated?

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What Is Polyhydramnios?

Polyhydramnios (sometimes simply called hydramnios) is a condition where there is an excess of amniotic fluid surrounding the baby growing in the womb. The baby floats around in the amniotic fluid, and swallows and breathes it in, and then releases it through urine. It is difficult to define exactly how much is excessive; the average volume of fluid at full-term is 800 ml, but a range of 400 to 1500 ml is accepted as normal. Probably only volumes in excess of 2000 ml would be considered abnormal on clinical examination. In most of the cases the excess fluid accumulates gradually (chronic hydramnios) and is only noticed after the 30th week. In a few exceptional cases hydramnios occurs earlier (around week 20) and more quickly (acute hydramnios), and many of these cases are associated with uniovular twins (identical or monozygotic twins which grow from a single fertilized egg which splits).

What Causes It?

The cause of hydramnios can be fetal or maternal related, although sometimes no specific cause is found.

Fetal Causes
• It is usually caused by the developing baby not swallowing amniotic fluid in normal amounts. This can happen if the baby has a health condition like esophageal atresia, an inability to swallow.
• Hydramnios often occurs with anencephaly (the absence of a large part of the brain and the skull).
• Hydramnios may also occur with other fetal abnormalities, including spina bifida, Down's syndrome or Edwards' syndrome.
• Chorioangioma (tumor) of the placenta is a rare cause.
• There may be excess fluid if hydrops fetalis (edema or swelling in the baby) develops.

Maternal Causes
• Hydramnios is more common in pregnant women with poorly controlled gestational diabetes. Not only is there an excess of amniotic fluid, but the placenta and fetus are larger than normal.
• An infection such as toxoplasmosis or parvovirus (slapped cheek disease) can cause the condition.

Symptoms And Clinical Signs

The physical signs depend on how much excess fluid there is. The more fluid, the more obvious the signs. Indications include:

• Tummy is particularly enlarged, much more so than expected for the time of pregnancy.
• The baby is unusually mobile.
• Abdominal pain and vomiting.
• It may be difficult to feel the baby kick and the fetal heartbeat may be muffled or difficult to hear. Your doctor may perform a karyotype test to measure the fetal heartbeat.
• Pregnancy symptoms like heartburn, constipation, swollen legs, varicose veins and stretch marks can be worse than normal.

How Is It Diagnosed?

During each prenatal visit your doctor or nurse will measure your belly. This tells them if your womb is growing faster than normal, or if it larger than expected for your baby's gestational age. If a problem is suspected you may have to come back sooner to be measured again, or he may perform an ultrasound scan. Twins or the presence of large ovarian cysts in pregnancy can make a diagnosis more difficult. If the doctor suspects a birth defect, you may need an amniocentesis to test for a genetic defect.

What Complications Can It Cause?

• It can simulate placental abruption meaning the placenta is separated from the uterus too early.
• It can cause spontaneous premature rupture of membranes.
• The extra fluid in the amniotic sac makes it difficult for the baby to settle his head down into the pelvis. If your waters break the umbilical cord can be pulled down (prolapse) into the vagina before the baby. This requires an emergency cesarean section.
• After delivery there is a risk of postpartum bleeding.
• The risk of infant mortality is greatly increased due to the risk of preterm labor and cord prolapse.

How Is It Treated?

There is no known method of controlling the production or absorption of amniotic fluid. The only thing a mother can do, if she has diabetes, is to ensure she has it properly under control. Mild polyhydramnios that shows up in the latter part of pregnancy does not often cause serious problems. If polyhydramnios produces no symptoms and there is no evidence of any fetal abnormality, the condition requires no treatment. Routine ultrasound examination at 16-18 weeks should ensure that fetal abnormalities are detected before hydramnios develops. If your baby has an abnormality which can be operated on, labor may need to be induced and the baby will be transferred to a neonatal surgical unit. A specialist surgeon will perform the operation.

If the baby appears normal but the mother is near term and is in serious discomfort, labor should also be induced. If there is a great deal of fluid there is some risk of placental separation after rupturing the membranes, and so some doctors draw off part of the fluid by amniocentesis before the induction. In this process an epidural needle is inserted into the amniotic sac and fluid is withdrawn with an epidural catheter passed through the needle. Up to 2 liters of fluid may be removed, provided that it is only allowed to escape slowly.

This process may also be performed on women who are still too early to induce, but for whom discomfort is unbearable. Although there is some risk of labor starting after amniocentesis the discomfort is relieved for a time. Unfortunately the fluid is often quickly replaced. The procedure can be repeated if necessary. There is always a slight risk of perforating a fetal vessel and causing bleeding into the amniotic sac.

  Related Articles on Hydramnios

For more information, see the following:

List of gynecological problems
Ovarian tumors during pregnancy.

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