An amniotic fluid index measures the amount of amniotic fluid surrounding the baby. It’s an important way for your doctor to assess your baby’s development and identify potential complications.

An amniotic fluid index (AFI) measures the amount of amniotic fluid in your uterus during pregnancy. It’s one important test that helps doctors and healthcare professionals determine how well your baby is and how your pregnancy is progressing.

This screening test is generally done at weeks 32–36 of pregnancy but may be done earlier if your pregnancy is considered high risk.

Amniotic fluid is the clear or yellowish fluid surrounding a fetus in the womb while they develop. It provides nourishment and a protective cushion, allowing space for the baby to grow and develop.

Here is what to know about your amniotic fluid index, how it’s measured, and what it tells doctors.

The AFI is a type of noninvasive ultrasound exam that shows how much amniotic fluid is in your uterus. Healthcare professionals perform it on pregnant people who are having only one baby (singleton gestation) and are at or past 24 weeks gestation.

An ultrasonographer will take four images of your abdomen – imagine a cross across your abdomen with the center at your belly button. Your AFI will measure the depth of the amniotic fluid seen in each of these four quadrants.

Based on how many weeks you are into your pregnancy, this measurement can tell your doctor how your pregnancy is progressing and if your baby has one of several prenatal conditions.

Your AFI can help your doctor plan your treatment during pregnancy.

An AFI can detect if you have atypical levels of amniotic fluid, including:

Polyhydramnios

Polyhydramnios is a condition in which you have too much amniotic fluid without any apparent cause (idiopathic). It’s often associated with an increased risk to the baby and the pregnant parent, linked to developmental changes in infants, such as chromosomal conditions, major fetal structural changes, and pregnancy complications.

Minor polyhydramnios may not require treatment. However, if you have severe polyhydramnios, you may need treatment, such as amnioreduction, medication, or hospitalization, to reduce the amount of amniotic fluid in your body.

Oligohydramnios

Oligohydramnios occurs when you have too little amniotic fluid. This condition often indicates changes in the baby’s kidneys.

While you can have oligohydramnios at any point during pregnancy, it’s more common in late pregnancy. Treatment will depend on what’s causing the oligohydramnios and may include:

  • monitoring with ultrasounds
  • bed rest
  • medication to treat underlying conditions like diabetes and hypertension
  • amnioinfusion
  • hospital admission
  • early delivery
  • treating conditions in the baby before they are born

Anhydramnionos

Anhydramnionos is a severe form of oligohydramnios when there is little to no amniotic fluid. When this happens, the fetus’ lungs can’t develop fully, and they may die after birth. There are treatment options to add fluid to your uterus during pregnancy.

What are normal amniotic fluid levels?

A typical amniotic fluid index measures 5 cm to 25 cm. A measurement of less than 5 cm is considered oligohydramnios, and a measurement greater than 25 cm is considered polyhydramnios.

AFI is typically performed after 24 weeks of pregnancy. However, if your doctor suspects a problem or if you have a high risk pregnancy, you may have this test more frequently.

What’s the difference between the amniotic fluid index (AFI) and single deepest pocket (SDP) measurement?

A single deepest pocket test examines only one quadrant during the ultrasound rather than the four measured during an AFI. This test is used if an individual needs to have an amniotic fluid assessment before 24 weeks of pregnancy or if they’re having multiple babies (twins, triplets, etc.).

Amniotic fluid index (AFI) is a prenatal test that uses ultrasounds to measure the amount and level of your amniotic fluid. This is one way your doctor can tell if you are at risk of complications and if the baby has specific conditions.

The test is noninvasive and painless. Generally, you need only one AFI, but if your pregnancy is high risk, you are having multiple babies, or have other complications, you may need additional AFIs.