When a woman is pregnant, the embryo develops inside the amniotic sac, a membrane full of amniotic fluid, which surrounds the baby and plays an important part in its development. Polyhydramnios occurs when there is too much amniotic fluid in the amniotic sac. This causes the uterus to grow excessively and can negatively affect fetal development. Polyhydramnios can occur as early as 16 weeks, though it is most common much later in the pregnancy. The rare condition affects one to two percent of pregnancies.
To understand polyhydramnios, it helps know a little about how a normal pregnancy develops. The amniotic sac forms about 12 days after conception. At this point, the amniotic fluid cushions and protects the embryo and helps maintain temperature. As the fetus develops, it breathes in the fluid to develop the lungs and swallows the fluid as the gastrointestinal system develops. Amniotic fluid also allows the baby to kick and move to aid muscle and bone development and prevents the umbilical cord from being squeezed.
At the beginning of a pregnancy, amniotic fluid is mostly composed of water that comes from the mother. Later, at around 20 weeks, the fluid is primarily fetal urine. The amount is regulated by the fetus swallowing the fluid and passing it back into the amniotic sac as urine. Polyhydramnios, or too much amniotic fluid, occurs for several reasons, particularly when this method of regulation is not effective.
One of the causes of polyhydramnios is an imbalance the amount of amniotic fluid the fetus is swallowing and the amount of urine being produced. Congenital disabilities that affect the baby's ability to swallow can cause this issue, including gastrointestinal problems or a central nervous system disorder. If considerably more fetal urine is produced than what the fetus is swallowing, amniotic fluid levels can rise.
The cause of polyhydramnios is difficult to determine and often remains a mystery. In addition to an imbalance between the amount of fluid the fetus swallows and the amount of urine it produces, causes include high blood glucose levels in the mother either before or during pregnancy, differing blood types between mother and baby, problems with the placenta, and twin to twin transfusion syndrome when carrying identical twins.
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Mild polyhydramnios usually does not have any signs or symptoms. In severe cases, more fluid makes the uterus larger, so symptoms are more pronounced. Women may experience shortness of breath, abdominal discomfort, swelling in the legs, and uterine cramping or contractions. The fetus may also be in a breech presentation. If a doctor or midwife has trouble feeling the baby and the uterus measures larger than it should at any point, they may suspect polyhydramnios.
When a physician suspects polyhydramnios, the first diagnostic test is a fetal ultrasound. This non-invasive test uses sound waves to produce images that allow medical professionals to assess the amount of amniotic fluid and monitor the fetus. If there is evidence of polyhydramnios, the doctor may perform a detailed scan to measure pockets of fluid, to determine the extent of the problem. An in-depth scan of the fetus can assess for complications.
Once a diagnosis of polyhydramnios is made, the mother often requires additional testing. Specific tests are based on risk factors and past medical history. They can include blood tests for infections as well as an amniocentesis. The latter procedure involves taking a sample of amniotic fluid, including fetal cells and chemicals made by the baby, that can be used to screen for chromosomal abnormalities.
Polyhydramnios can have complications for both the mother and the baby. Placental abruption may occur, which is when the placenta detaches from the uterine wall. Early labor and premature birth are possibilities, and the baby may be in breech position. C-sections are common for deliveries when the mother has polyhydramnios. There is a chance that the umbilical cord could fall out of the birth canal before the baby is born during vaginal delivery. Additionally, the mother may experience excessive bleeding.
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When a woman is diagnosed with polyhydramnios, her doctor will monitor her pregnancy more closely. He or she may conduct a nonstress test that checks the heart rate of the fetus during activity. During this test, the mother wears a special monitor that reads the baby's heart rate. To get the baby to move, the mother may be asked to drink or eat. Sometimes, a buzzer encourages movement or wakes the fetus if it is sleeping. Another test is a biophysical profile, a detailed ultrasound that measures the baby's breathing, movement, and tone and takes a more accurate measurement of the amount of amniotic fluid.
Mild cases usually do not require treatment and may resolve on their own as the pregnancy progresses. Treating the underlying cause, such as an infection or diabetes, may resolve some cases of polyhydramnios. Severe cases often require interventions such as draining the excess amniotic fluid with amniocentesis. Medication can reduce fetal urine output to lower amniotic fluid volume. The baby's heart may need to be monitored closely using an echocardiogram. Mild to moderate cases usually carry to term. In severe polyhydramnios, the baby may require early delivery to avoid complications.
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