Polyhydramnios is an excess accumulation of amniotic fluid – the protective liquid that surrounds the unborn baby in the uterus during pregnancy. The condition occurs in 1 percent to 2 percent of all pregnancies.
Polyhydramnios can be an isolated condition (which means no other birth defect or condition occurs with it), but it is also more common when the unborn baby has certain congenital anomalies (such as duodenal atresia) or a medical condition involving the heart or lungs (such as hydrops fetalis). Polyhydramnios is also associated with various genetic disorders, including Down syndrome (Trisomy 21) and Edward’s syndrome (Trisomy 18), but only when the baby also has duodenal atresia or other blockages in the gastrointestinal tract.
Severe polyhydramnios symptoms may cause a pregnant woman to experience shortness of breath or other discomforts due to the abdomen becoming overly distended. In addition, the condition raises the risk of problems during pregnancy and childbirth, including preterm labor, premature rupture of the amniotic sac (also known as “water breaking”), and placental abruption (the peeling away of the placenta from the inner wall of the uterus). Polyhydramnios is also sometimes associated with a condition known as intrauterine growth restriction (IUGR), which occurs when the unborn baby’s weight is significantly smaller than expected for its gestational age.
There are few recent studies but polyhydramnios is said to affect 0.2-1.6% of all pregnancies. Rates are much higher in pregnancies for women with diabetes or gestational diabetes.
Where polyhydramnios is mild, an underlying abnormality is found in only 17%, whereas in moderate-to-severe polyhydramnios, this figure rises to 91%. There is also an association with increasing maternal age and with fetal macrosomia.
Types of Polyhydramnios
There are two clinical varieties of polyhydramnios.
- Chronic polyhydramnios where excess amniotic fluid accumulates gradually.
- Acute polyhydramnios where excess amniotic fluid collects rapidly.
Risk factors for developing polyhydramnios
- Mothers who are carrying multiple babies. This is because of the size of the placenta and the amount of space it occupies in the uterus.
- Mothers with gestational diabetes which is not being treated effectively.
- When identical twins are present and they have developed twin-to-twin transfusion. This is a condition which can arise when one baby is receiving more blood flow than the other.
- In many cases, the cause for polyhydramnios is unknown.
Pathophysiology of Polyhydramnios
The volume of amniotic fluid increases steadily until 33 weeks of gestation. It plateaus from 33-38 weeks, and then declines – with the volume of amniotic fluid at term approximately 500ml.
It is predominantly comprised of the fetal urine output, with small contributions from the placenta and some fetal secretions (e.g. respiratory, oral).
The fetus breathes and swallows the amniotic fluid. It gets processed, fills the bladder, and is voided, and the cycle repeats. Problems with any of the structures in this pathway can lead to either too much or too little fluid.
Causes of Polyhydramnios
In about half of cases, polyhydramnios has no known cause. In the other half, polyhydramnios may be caused by:
- Birth defects that affect swallowing (which helps regulate amniotic fluid levels)
- Uncontrolled maternal diabetes (high blood glucose levels can cause the baby to pee more often)
- An abnormal fetal heart rate
- An infection in the baby
- Blood incompatibilities between mom and baby (like Rh and Kell diseases)
- Twin-to-twin transfusion syndrome
- Low red blood cell count in the baby (anemia)
For women experiencing a mild case of polyhydramnios, there may not be any symptoms. Women experiencing a more severe form of the condition could have these symptoms:
- A sensation of tightness in the stomach
- Difficulty with bowel movements (constipation)
- Producing less urine
- Enlargement of vulva
- Breathing troubles
- Swelling of leg, thigh, hip, ankle and/or foot
Larger abdomen with excessive stretch marks- A symptom of polyhydramnios
The most significant complications associated with polyhydramnios include:
Prematurity: Excess amniotic fluid levels can trigger pre-term labor and increase the chances of a baby being born prematurely. This is a concern because prematurity greatly increases a baby’s risk of various health problems and complications including birth injuries.
Fetal Macrosomia: Polyhydramnios is commonly associated with excess fetal growth which can develop into fetal macrosomia. Macrosomic babies cannot be safely delivered via vaginal delivery.
Placental Abruption: This is a very dangerous complication in which the placenta prematurely separates from the wall of the uterus before the baby is ready for delivery. This creates an emergency event that must be quickly diagnosed and managed to avoid injury to the baby.
Fetal Malposition: When there is too much amniotic fluid in the womb it has a tendency to cause malposition of the fetus (e.g., breech, transverse, etc.) which can complicate a vaginal delivery.
Umbilical Cord Prolapse: This is one of the most dangerous delivery complications which occurs when the umbilical cord drops down into the birth canal in front of the baby during delivery, creating a major risk of oxygen deprivation.
Diagnosis and test
Your healthcare provider will examine you and ask about your symptoms. Tell your doctor if your baby is moving less than usual, or if any fluid leaking from your vagina. Tell him about all medicines you are taking. You may need any of the following:
Ultrasound pictures are used to find the amount of amniotic fluid in the womb. The pictures may also show the baby’s size. Baby kidneys and urinary tract will be checked. Moving ultrasound pictures are used to check blood flow through arteries in the baby’s kidneys and through the placenta.
Amniocentesis is a procedure used to take a sample of amniotic fluid from the womb. The fluid contains cells that can be tested for birth defects and other problems.
A glucose challenge test is used to find the amount of glucose (sugar) in your blood. An increased amount may be a sign of gestational diabetes (diabetes during pregnancy). You will fast overnight and then drink a sweet liquid. Your blood sugar level will be tested every hour for 3 hours in a row. A high level in at least 2 of the tests is a sign of gestational diabetes.
A fetal nonstress test is used to check how the baby’s heartbeat changes when he moves. You will wear a device on your abdomen. The device measures your baby’s heart rate. You may need to eat or drink something to make your baby more active.
A biophysical profile is a test that checks the baby’s breathing and movement. It also checks for the amount of amniotic fluid in the womb.
Treatment and medications
Mild cases of polyhydramnios may not require treatment, but doctors should have their patients come in for extra prenatal check-up’s to monitor the condition and make sure it does not become severe. Treatments for more severe forms of polyhydramnios sometimes focus on addressing the underlying causes.
Additional treatments/interventions include:
Amnioreduction: This involves using a long needle to drain excess amniotic fluid from the uterus. There are certain risks associated with this, which doctors must weigh when deciding whether it is an appropriate intervention.
Medications to reduce the amount of fetal urine: This can put the fetus’s heart health at risk, so again, doctors must be careful in determining whether this is the right path. They must also carefully monitor the baby for signs of fetal distress.
Bed rest: This can help delay preterm labor in cases of moderate polyhydramnios
This condition cannot always be prevented. Proper care before and during pregnancy may help lower the risk.