Amniotic fluid index is a way of measuring the amount of liquid that is around a baby (fetus) in the uterus during pregnancy. It is usually done as part of the biophysical profile (BPP), which is a series of tests that measure the health of the baby during pregnancy.

Amniotic fluid protects the fetus from temperature extremes and from being bumped or hurt as the mother moves around. It also allows the fetus to move around in the uterus and is important for lung and limb development. A problem with the amount of amniotic fluid could point to a problem with the growing fetus. Too much or too little fluid could also cause problems during labor and delivery.

Doctors use ultrasound to calculate the amniotic fluid index. The doctor looks at the amount of amniotic fluid in four different areas of the uterus. The four areas are called quadrants. The doctor measures how much fluid is in each quadrant. Then he or she adds up the numbers to get an idea of the total amount of fluid that surrounds the baby.

• If there is less than 5 centimeters (cm) of fluid, it means that there is too little fluid. This is called oligohydramnios. It can affect how the baby grows and can lead to complications during labor and delivery.
• If there is more than 24 cm of fluid, it means that there is too much fluid. This is called polyhydramnios. It can cause the amniotic sac to break too soon. It can also cause preterm labor and stillbirth.