Amniotic fluid has many important functions and is vital for healthy fetal development. However, if the amount of amniotic fluid inside the uterus is too little or too great, complications can occur.
This article looks at the many functions of amniotic fluid, as well as what happens when the levels of amniotic fluid are either too high or too low.
Here are some key points about amniotic fluid. More detail and supporting information is in the main article.
- At first, amniotic fluid consists of water from the mother's body, but gradually, the larger proportion is made up of the baby's urine.
- It also contains important nutrients, hormones, and antibodies and it helps protect the baby from bumps and injury.
- If the levels of amniotic fluid levels are too low or too high, this can pose a problem.
What is amniotic fluid?
Amniotic fluid protects and nourishes the baby in the womb.
While a baby is in the womb, it is situated within the amniotic sac, a bag formed of two membranes, the amnion, and the chorion. The fetus grows and develops inside this sac, surrounded by amniotic fluid.
Initially, the fluid is comprised of water produced by the mother. By around 20 week's gestation, however, this is entirely replaced by fetal urine, as the fetus swallows and excretes the fluid.
Amniotic fluid also contains vital components, such as nutrients, hormones, and infection-fighting antibodies.
When amniotic fluid is green or brown, this indicates that the baby has passed meconium before birth. Meconium is the name of the first bowel movement.
Meconium in the fluid can be problematic. It can cause a breathing problem called meconium aspiration syndrome that occurs when the meconium enters the lungs. In some cases, babies will require treatment after they are born.
Amniotic fluid is responsible for:
- Protecting the fetus: The fluid cushions the baby from outside pressures, acting as a shock absorber.
- Temperature control: The fluid insulates the baby, keeping it warm and maintaining a regular temperature.
- Infection control: The amniotic fluid contains antibodies.
- Lung and digestive system development: By breathing and swallowing the amniotic fluid, the baby practices using the muscles of these systems as they grow.
- Muscle and bone development: As the baby floats inside the amniotic sac, it has the freedom to move about, giving muscles and bones the opportunity to develop properly.
- Lubrication Amniotic fluid prevents parts of the body such as the fingers and toes from growing together; webbing can occur if amniotic fluid levels are low.
- Umbilical cord support: Fluid in the uterus prevents the umbilical cord from being compressed. This cord transports food and oxygen from the placenta to the growing fetus.
Normally, the level of amniotic fluid is at its highest around 36 of pregnancy, measuring around 1 quart. This level decreases as birth nears.
When the waters break, the amniotic sac tears. The amniotic fluid contained within the sac then begins to leak out via the cervix and vagina.
The waters usually break toward the end of the first stage of labor. According to Today's Parent, only about 15 percent of waters break upon the onset of labor. When this happens, it is time to contact the health provider as delivery may be imminent.
Some conditions can cause there to be more or less than the normal amounts of amniotic fluid.
Oligohydramnios is when there is too little amniotic fluid.
Polyhydramnios, also referred to as hydramnios or amniotic fluid disorder, is when there is too much fluid.
Low levels of amniotic fluid, referred to as oligohydramnios, occur in 4 percent of all pregnancies and 12 percent of post-date pregnancies.
This may be evident in cases of leaking fluid from a tear in the amniotic membranes, measuring small for a certain stage of pregnancy or if the fetus is not moving as much as it would be expected to.
It may also occur in mothers with a history of any of the following medical conditions:
- prior growth-restricted pregnancies
- chronic high blood pressure (hypertension)
- problems with the placenta, for example, abruption
- multiple pregnancies, for example twins or triplets
- birth defects, such as kidney abnormalities
- delivering past the due date
- other unknown reasons, known as idiopathic
Oligohydramnios can happen during any trimester but is a more concerning problem during the first 6 months of pregnancy. During that time, there is a higher risk of birth defects, loss of pregnancy, preterm birth, or neonatal loss of life.
If fluid levels are low in the last trimester, the risks include:
- slow fetal growth
- labor complications
- the need for a Cesarean delivery
The rest of the pregnancy will be monitored closely to ensure normal development is taking place.
Doctors may use the following tests:
- Nonstress tests: This is to check the baby's heartbeat when it is resting and when it is moving.
- Biophysical profiling: An ultrasound scan can detect the baby's movements, muscle tone, breathing and amniotic fluid levels. This may be followed up with a nonstress test.
- Fetal kick counts: This is to time how long it takes for the baby to kick a certain number of times.
- Doppler studies: These use sound waves to check the flow of blood in the baby.
In some cases, doctors may decide that labor will need to be induced, in order to protect the mother or the child. Amnioinfusion (the infusion of saline into the uterus), increasing maternal fluids, and bed rest may also be necessary.
There is a higher chance of labor complications, due to the risk of umbilical cord compression. Amnioinfusion may be needed during labor. In some cases, a cesarian delivery may be necessary.
When there is too much amniotic fluid, this is called polyhydramnios. According to the American Pregnancy Association, it occurs in 1 percent of all pregnancies.
Polyhydramnios is present when the AFI is more than 24 centimeters (cm) and the MVP measures more than 8cm.
Fetal disorders that can lead to polyhydramnios include:
- gastrointestinal disorders, including duodenal or esophageal atresia, gastroschisis, and diaphragmatic hernia
- brain or nervous system disorders, such as anencephaly or myotonic dystrophy
- achondroplasia, a bone growth disorder
- fetal heart rate problems
- Beckwith-Wiedemann syndrome, which is a congenital growth disorder
- fetal lung abnormalities
- hydrops fetalis, in which an abnormal level of water builds up inside multiple body areas of a fetus
- twin-to-twin transfusion syndrome, where one child gets more blood flow than the other
- mismatched blood between mother and child, for example Rh incompatibility or Kell diseases
Poorly controlled maternal diabetes also increases the risk.
Too much fluid can also be produced during multiple pregnancies, when the mother is carrying more than one fetus.
Maternal symptoms can include abdominal pain and difficulty breathing due to the enlargement of the uterus.
Other complications include:
- preterm labor
- premature rupture of membranes
- placental abruption
- postpartum hemorrhage
- fetal malposition
- cord prolapse
Testing for maternal diabetes may be recommended, and frequent ultrasounds will be obtained to monitor the levels of amniotic fluid in the uterus.
Mild cases of polyhydramnios typically resolve without treatment.
In more severe cases, fluid may need to be reduced with either amniocentesis or a medication called indomethacin. This reduces the amount of urine the baby produces.
Leaking amniotic fluid
Sometimes, fluid leaks before the waters break. According to the American Pregnancy Association, only 1 in 10 women will experience a dramatic flow of fluid as the waters break. For most, it will start as a trickle, or leak.
Sometimes, what looks like fluid leaking is actually urine, because the uterus is pressing on the bladder.
If the fluid has no color and no smell, it will be amniotic fluid, and you should contact a healthcare provider as labor will normally begin soon.
If the fluid is green, brownish-green, or foul-smelling, this may indicate the presence of meconium or an infection. Medical advice should be sought.
Premature rupture of membranes
If leaking or rupture happens before 37 weeks, this is known as premature rupture of membranes (PROM). Depending on how early this happens, it can have serious consequences for the mother and the unborn child. It affects around 2 in 100 pregnancies.
This is known as premature rupture preterm, but it is also possible to have premature rupture at term. That is when 37 weeks or more of pregnancy are complete, but labor does not start spontaneously within 6 hours of the membrane rupturing.
It is important to seek medical help as soon as possible and to avoid having sex or introducing anything into the vagina, as this could lead to an infection.
Anyone who is concerned about leaking or levels of amniotic fluid during pregnancy should discuss this with their healthcare provider.