The amniotic fluid that fills the uterus during pregnancy serves multiple purposes:
- It protects the fetus from physical injury by providing a cushion against impact.
- It ensures proper bone and limb growth by allowing the fetus to move about freely.
- The fetus breathes the amniotic fluid while it is in the womb; this is necessary for proper lung development. The fetus also urinates during development, which is a major source of amniotic fluid in the second half of pregnancy.
- It protects the fetus from loss of body heat.
Because of the important role that amniotic fluid plays in fetal development and well being, an excess or deficiency of this fluid can potentially cause problems, or it can be a sign of some other problem.
An excess of fluid in the amniotic sac is called polyhydramnios. This condition has the potential to cause serious pregnancy complications, including abnormal fetal positioning, placental abruption, and others. Fortunately, polyhydramnios occurs in only about 1 percent of pregnancies, and most women who have this condition deliver normal, healthy babies.
Causes of Polyhydramnios
The cause of this condition cannot always be determined, but it is often associated with:
- Twins and multiples
- Gestational diabetes (in some cases, if diabetes is the cause of polyhydramnios, the baby may be unusually large for its gestational age)
- Gut atresia, a blockage in the baby’s digestive system that can interfere with the absorption of amniotic fluid (this will usually require surgery after the baby is born)
- Rh disease, an incompatibility between maternal and fetal blood types
- Twin-to-twin transfusion syndrome, a condition in which a pair of identical twins in separate sacs share the placenta and one twin does not receive sufficient blood flow while the other gets too much (too much blood flow leads to excess amniotic fluid around that twin)
- Other birth defects such as spina bifida or congenital heart defects
- Certain intrauterine infections which can cause severe fetal anemia can lead to polyhydramnios
- Placental chorioangioma, a type of benign tumor that appears on the placenta
Symptoms of Polyhydramnios
The buildup of excess amniotic fluid tends to happen gradually, but in most cases it will be noticeable to your doctor by the 30th week of pregnancy and may be detectable by ultrasound as early as the 20th week. In rare cases it can happen more quickly and may be detectable earlier. Normally there are no symptoms, other than having a larger pregnant belly than expected for your gestational age.
If your belly seems to grow suddenly at what appears to be an abnormal rate, you may have what is known as acute polyhydramnios, and you should see your doctor as soon as possible. Symptoms you may notice at home include:
- Shortness of breath due to increased pressure on your diaphragm and lungs
- Decreased urination (if the fluid build-up is rapid, your tissues can become dehydrated)
If your doctor suspects that you have too much amniotic fluid, he or she will probably recommend an ultrasound test in order to measure it. This measurement will determine the amniotic fluid index (AFI), a number that reflects the depth of fluid in the deepest pocket of the uterus. An AFI of 20–25 is borderline, and greater than 25 is definitive polyhydramnios. An alternate definition is a single pocket of fluid greater than 8 cm in any dimension.
Risks of Polyhydramnios
Whether polyhydramnios is a problem depends somewhat on how much excess fluid has accumulated, how quickly, and why the condition is present. Mild cases appearing late in pregnancy are rarely a cause for concern, but severe cases are associated with an elevated risk for placental abruption, as well as for certain birth defects. Maternal urinary tract infections are another possibility. It is important to remember, however, that the vast majority of cases end with the birth of normal, healthy babies.
Labor complications that can result from this condition:
- Preterm labor may be brought on by excess pressure in the womb caused by the womb being larger than normal. Abruption (separation of the placenta prior to delivery) can occur if the water bag breaks. The sudden loss of large amounts of fluid can cause the uterus to shrink so much that a portion of placenta may detach.
- The fetus may assume the wrong position in the uterus, as there is so much fluid the baby is kind of floating inside the amniotic sac.
- The umbilical cord may slip into an abnormal position; for example, it may slip down into the birth canal during labor, a condition known as umbilical cord prolapse.
Treatment of Polyhydramnios
If your doctor believes that the excess amniotic fluid has the potential to cause problems, he or she may recommend amniocentesis in order to test for chromosomal abnormalities. Amniocentesis may also be performed in order to drain the excess fluid from the amniotic sac. Alternatively, your doctor may prescribe indomethacin, a drug that reduces the volume of amniotic fluid by decreasing the fetus’ production of urine. Indomethacin isn’t recommended if pregnancy has advanced beyond 30 weeks, however, and it may be associated with some risk of fetal heart problems, according to the Mayo Clinic.
Oligohydramnios is the opposite condition to polyhydramnios—an insufficiency of amniotic fluid. It is about as common, occurring in 4 percent of pregnancies (1 out of 25). It can happen at any time during pregnancy, although it is more common in the third trimester.
Symptoms of Oligohydramnios
Your doctor will be monitoring your pregnancy and may notice signs of this condition, such as too little weight gain or overly slow growth of the fetus, based on a uterine size smaller than expected. If you are leaking water from your vagina, however, you should tell your doctor immediately, as this is an important sign. Regardless of the reason why, if your doctor suspects oligohydramnios he or she will check your AFI via ultrasound.
Causes of Oligohydramnios
Some of the causes of this condition include:
- Fetal Intrauterine Growth Restriction (IUGR)
- Maternal high blood pressure or pre-eclampsia
- Certain birth defects affecting the fetus’ kidneys
- Maternal Diabetes (long-standing, not gestational)
- Post-term pregnancy(overdue)
- Premature rupture of the membranes (PROM)—this is when the amniotic sac breaks (in layman’s terms, your water breaks) before the onset of labor.
Complications of Oligohydramnios
Like polyhydramnios, oligohydramnios can potentially cause or lead to premature birth. In severe cases it can result in birth defects, including clubfoot and other musculoskeletal or limb abnormalities. It can also cause miscarriage or stillbirth. These severe problems are more likely if the condition appears early in pregnancy such as in the second trimester.
If the deficiency in amniotic fluid occurs during the third trimester it can be associated with fetal growth problems, and there is a greater chance that the fetus may need to be delivered earlier than expected. Also complications may arise during labor that could result in the need for a C-section delivery. For example, oligohydramnios can cause the umbilical cord to be squeezed during labor, depriving the baby of oxygen.
Treatment of Oligohydramnios
If it occurs near the end of an otherwise healthy pregnancy, this condition may not require treatment at all. Sometimes close observation and waiting for labor to begin naturally is the best option. In some cases your doctor may want to induce labor early, and with severe oligohydramnios, sometimes proceeding directly to a
C-section birth is the best course of action.
Patients with oligohydramnios always think that they need to drink more water. We wish it were that easy to fix this problem! The water the patient drinks has almost no relationship to the water around the baby. Amniotic fluid is a product of placental blood flow and fetal circulation, so it is NOT advised to drink large amounts of water in an attempt to increase amniotic fluid. If your fluid intake is very low, then you should increase it to normal levels (4–6 glasses of water a day).
Bedrest for a few hours per day is often advised to help improve placental blood flow. Lying on the side (left or right) is usually preferred if the bedrest is for this specific reason.
During labor, one treatment might be amnioinfusion, a procedure in which a saline solution is injected into the amniotic sac to make up for the insufficiency of amniotic fluid. The usual purpose of amnioinfusion is merely to enhance ultrasound images, however, and the increase in fluid volume is generally short-lived.
Questions to Ask Your Doctor About Oligohydramnios and Polyhydramnios
- Do you recommend that I undergo amniocentesis?
- Do you recommend that we induce labor rather than waiting for it to occur naturally?
- Is my baby at risk for any type of birth defect?
- Is my diabetes cause for concern?
- Is my blood pressure cause for concern?
- Will I need to deliver via C-section?