Amniotic fluid is a clear to slightly yellow liquid that surrounds a fetus within the amniotic sac. The developing fetus floats in amniotic fluid for the duration of a pregnancy.

Amniotic fluid is present at the formation of the amniotic sac, around 12 days after you become pregnant. This is a thin-walled sac that contains the fetus during pregnancy.

When the fluid first starts to form inside the amniotic sac, it’s mostly made of your own body fluids. But when baby’s kidneys kick in and start passing urine (as early as 11 weeks), those new fluids start building up to help cushion and protect baby’s growing body. After around week 20, the amniotic fluid is mostly urine.

At around 34 weeks gestation, roughly 800 milliliters (mL) of amniotic fluid surrounds the fetus. At a full-term pregnancy of 40 weeks gestation, roughly 600 mL of amniotic fluid remain.
Amniotic fluid is made up of 98% water and electrolytes, along with peptides, carbohydrates, and signalling molecules. The remaining 2% is made up of lipids and hormones.

Amniotic fluid primarily protects the fetus from harm but serves a number of purposes during pregnancy. The functions of the amniotic fluid include:

  • Acts as a cushion: This protects the fetus from injury should the parent’s abdomen be the subject of trauma or a sudden impact.
  • Protecting the umbilical cord: Amniotic fluid flows between the umbilical cord and fetus. The fluid prevents the umbilical cord from compressing
  • Protecting from infection: Amniotic fluid has antibacterial properties.
  • Containing essential nutrients: These include proteins, electrolytes, immunoglobulins, and vitamins that assist in the development of the fetus.
  • Allowing for the fetus to move: Amniotic fluid also allows the developing fetus to move around in the uterus, which in turn allows for proper development and growth of the musculoskeletal system, gastrointestinal system, and pulmonary system.
  • Maintaining temperature: Amniotic fluid assists in keeping a constant steady temperature around the fetus throughout pregnancy, protecting against heat loss.

Amniotic fluid is normally clear however when the fetus has passed meconium (their first poop) in your uterus it will have a green to brownish tinge to it. Please contact your local maternity unit immediately if this is seen.

Meconium in amniotic fluid can cause complications if the fetus breathes it in. In severe cases, the fetus may develop meconium aspiration syndrome and need immediate treatment after birth.

What does Amniotic Fluid smell like?
Amniotic fluid should be odourless. Contact your healthcare provider if you notice a foul smell as it could be meconium-stained or mean there is an infection.

How is Amniotic Fluid measured?
Healthcare providers measure amniotic fluid using ultrasound. They measure pockets of amniotic fluid in specific areas of the amniotic sac.

What happens when you have low Amniotic Fluid?
Low amniotic fluid is called oligohydramnios. Low amniotic fluid affects about 4% of pregnant women. Several factors can contribute to low amniotic fluid. Some of them are:

  • Congenital conditions that affect the fetus’s kidneys or urinary tract.
  • Going more than two weeks past your due date.
  • Gestational diabetes.
  • Growth-restricted babies.
  • Early rupture of membranes.
  • Problems with the placenta.
  • Twins that share the same placenta.

Complications of low amniotic fluid.
Having too little amniotic fluid can lead to complications, especially in the first two trimesters. These can include:

  • Birth defects
  • Preterm birth
  • Miscarriage
  • Stillbirth
  • Infection

Third trimester oligohydramnios may lead to slow growth, umbilical cord compression, and a higher chance of labour problems or C-section delivery.

What happens if you have too much amniotic fluid?
Too much amniotic fluid is called polyhydramnios. It is a rare condition that happens in 1% of pregnancies and causes symptoms like swollen feet, breathlessness or constipation..

Moderate to severe polyhydramnios could be caused by:

  • A congenital condition affecting the fetus’s ability to swallow.
  • Gestational diabetes.
  • Carrying identical twins with transfusion syndrome (TTTS).
  • Problems with the fetus’s stomach.
  • Issues with the placenta.

Complications of too much amniotic fluid include:
Too much amniotic fluid in your uterus puts pressure on your nearby organs and causes pregnancy complications. Usually, polyhydramnios isn’t harmful, but it may cause serious complications. The condition is usually more serious if it occurs early in pregnancy because there’s more time for amniotic fluid to continue to build up. 

  • Early labour.
  • Premature birth (your baby is born before 37 weeks).
  • Placental abruption.
  • Postpartum haemorrhage.
  • Umbilical cord prolapse.
  • The fetus becomes breech.
  • Stillbirth.

If you have any concerns about the information discussed in this blog post, you should consult with your healthcare provider.