Amniotic fluid is a clear, yellow fluid that is present within the amniotic sac during the first 12 days after conception. It encircles the growing baby in the uterus.
Amniotic fluid has several essential functions and is vital for healthy fetal development. However, if there is too little or too great an amount of amniotic fluid inside the uterus, complications can occur.
This article discusses the various roles of amniotic fluid, and what happens when amniotic fluid levels are either too high or too low.
Important facts about amniotic fluid
- 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?
While a baby is in the womb, it is inside the amniotic sac, a bag consisting of two membranes, the amnion and the chorion. Within this sac the fetus grows and develops, surrounded by an amniotic fluid.
Initially the fluid is made up of mother-generated water. However this is completely replaced by fetal urine by about 20 weeks gestation, when the fetus swallows and excretes the fluid.
Amniotic fluid as well contains vital components, such as nutrients, hormones, and infection-fighting antibodies.
It means that when amniotic fluid is green or brown the baby has absorbed meconium before birth. The term for the first bowel movement is Meconium.
Meconium can be problematic in the fluid. It may cause meconium aspiration syndrome, a breathing issue that happens when the meconium reaches the lungs. Babies can in some cases need treatment after birth.
Functions
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. As birth nears, this level decreases.
The amniotic sac gets tears when the waters break. The amniotic fluid inside the sac then starts flowing out of the cervix and vagina.
Usually the waters split at the end of the first labor stage. Only about 15 percent of waters break upon the onset of labor, according to Today ‘s Parent. It is time to contact the healthcare professional when this happens, as delivery can be imminent.
Disorders
Some conditions can cause amniotic fluid to be more or less than the normal amounts.
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.
Oligohydramnios
Low levels of amniotic fluid, or oligohydramnios, occur in 4% of all pregnancies, and 12% of post-date pregnancies.
Oligohydramnios is present when the ultrasound value of the amniotic fluid index (AFI) is less than 5 cm (the normal index is 5-25 cm) and the vertical maximum pocket (MVP) is less than 2 cm.
This can be evident when leaking fluid from a tear in the amniotic membranes, measuring small for a certain stage of pregnancy, or when the fetus does not move as much as expected.
For mothers with a history of any of the following medical conditions, this may also happen:
- prior growth-restricted pregnancies
- chronic high blood pressure (hypertension)
- problems with the placenta, for example, abruption
- preeclampsia
- diabetes
- lupus
- 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 occur during any trimester but during the first 6 months of pregnancy it is more of a concern. There is a greater chance of birth defects, loss of pregnancy, premature birth or neonatal loss of life during that period.
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.
For certain cases , doctors may agree that to protect the mother or the infant, labor may need to be induced. Amnioinfusion (saline infusion into the uterus), an increase in maternal fluids, and bed rest may also be needed.
Due to the risk of umbilical cord compression, there is a greater chance of labor complications. During labor, amnioinfusion can be required. In certain cases it may be appropriate to offer a cesarian delivery.
Polyhydramnios
This is called polyhydramnios, when there is too much amniotic fluid. It happens in 1 percent of all births, according to the American Pregnancy Association.
Polyhydramnios occurs when the AFI reaches 24 centimeters (cm) and the MVP measures more than 8 cm.
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
- infection
- 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 increases risks as well.
During multiple pregnancies too much fluid may also be created when the mother carries more than one fetus.
Maternal symptoms can include abdominal pain, and breathing problems due to uterine enlargement.
Other complications include:
- preterm labor
- premature rupture of membranes
- placental abruption
- stillbirth
- postpartum hemorrhage
- fetal malposition
- cord prolapse
Maternal diabetes testing can be recommended, and regular ultrasounds are obtained to monitor the amniotic fluid levels in the uterus.
Mild cases of polyhydramnios typically resolve untreated.
For more serious cases, either amniocentesis or a medication called indomethacin may need to minimize the fluid. Which reduces the amount of urine released by the infant.
Leaking amniotic fluid
Fluid leaks sometimes before waters break. Only 1 in 10 women will feel a rapid flood of fluid as the waters break, according to the American Pregnancy Association. It’ll start as a trickle, or leak, for most.
Occasionally, since the uterus is pulling on the bladder, what appears like fluid leaking is actually urine.
If there is no color and no smell in the fluid, it will be amniotic fluid, and you should contact a health care provider as work normally starts soon.
This may suggest the existence of meconium or an infection if the fluid is green, brownish-green or foul-smelling. Medical advice should be sought.
Premature rupture of membranes
If leakage or rupture occurs before 37 weeks this is called premature membrane rupture (PROM). It can have serious consequences for the mother and the unborn child, depending on how early that happens. Around 2 in 100 pregnancies are affected.
It is known as premature preterm rupture, but premature rupture is also possible on term. That is when 37 weeks of pregnancy or more are complete, but labor does not start spontaneously within 6 hours of the rupture of the membrane.
As this may lead to an infection, it is necessary to seek medical attention as soon as possible and to stop having intercourse or putting something into the vagina.
Someone who concerns about leakage or amniotic fluid levels during pregnancy should discuss this with their health care provider.