Amniotic fluid is a clear, yellow fluid which is found within the first 12 days following conception within the amniotic sac and surrounds the growing baby in the uterus.1-4
Amniotic fluid has many important functions and is vital for healthy fetal development.1,2 However, if the amount of amniotic fluid inside the uterus is too little or too great, complications can occur.
This Knowledge Center article will describe the many functions of amniotic fluid, as well as what happens when the levels of amniotic fluid are either too high or too low.
Fast facts on amniotic fluid
Here are some key points about amniotic fluid. More detail and supporting information is in the main article.
- To begin with, amniotic fluid consists of water from the mother's body
- Eventually, the majority of the amniotic fluid in the uterus is comprised of the baby's urine
- Amniotic fluid also contains important nutrients, hormones and antibodies
- Amniotic fluid helps protect the baby from bumps and potential injury
- As its body develops, the baby breathes and swallows the amniotic fluid
- Doctors can tell from the amount of amniotic fluid present whether or not a baby has a problem with their swallowing reflex
- Oligohydramnios refers to when amniotic fluid levels are too low
- Polyhydramnios refers to when amniotic fluid levels are too high
- Doctors can alter the levels of fluid within the uterus with a variety of procedures.
What is amniotic fluid?
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) in which the fetus grows and develops. Inside the sac, the baby is surrounded by amniotic fluid.5
Amniotic fluid is vital to the healthy growth and development of a fetus.
Initially, the fluid is comprised of water produced by the mother. It is soon entirely replaced by fetal urine (as it swallows and excretes the fluid), however, around 20 week's gestation.1
Amniotic fluid is not only comprised of urine, it also contains vital components such as nutrients, hormones and infection-fighting antibodies.1
When amniotic fluid is green or brown, this indicates that the baby has passed meconium (the first bowel movement) before birth. This can be problematic, causing 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.1
Amniotic fluid is responsible for:1-4
- 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 the 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.
Under normal circumstances, the level of amniotic fluid is at its highest during weeks 34-36 of pregnancy, measuring out at an average of 800 mL. This level decreases as birth nears, averaging around 600 mL at 40 weeks of gestation.1-3
When an expectant mother's waters break, the amniotic sac tears. The amniotic fluid contained within the sac then begins to leak out via the cervix and vagina. Most women's waters break toward the end of the first stage of labor. Once the waters have broken, the maternity unit should be contacted.6
At times, there may be conditions which cause a woman to have more or less than normal amounts of amniotic fluid. Oligohydramnios is the presence of too little amniotic fluid, whereas polyhydramnios - also referred to as hydramnios or amniotic fluid disorder - is the presence of excess fluid.
On the next page, we look in more detail at oligohydramnios and polyhydramnios, the condition that is also known as amniotic fluid disorder.