HomePregnancyAmniotic Fluid (AFI): Causes of Low AFI & Normal Range

Amniotic Fluid (AFI): Causes of Low AFI & Normal Range


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The Amniotic sac holds the developing foetus and is formed nearly 12 days after conception. The amniotic sac is filled with the amniotic fluid- a vital fluid that surrounds the foetus during pregnancy. It protects and provides nutrition to the foetus. 

A pregnant woman does not alone carry the weight of the baby but has to bear a combined weight of the placenta and amniotic fluid along with the baby.

The amniotic sac carries the below-given functions

  • It gives a cushioning effect to the baby while protecting it,
  • It helps regulate the temperature around the foetus,
  • It helps the foetal lungs develop and in easy breathing,
  • The baby swallows the amniotic fluid, and it helps the foetal digestive tract develop,
  • It helps the baby move while strengthening its muscles and bones,
  •  It also protects the umbilical cord- the crucial lifeline of the baby that transfers oxygen and food from the placenta. 

The amniotic fluid is nutrient-rich and chemically made of hormones and antibodies. The amniotic fluid measurement during prenatal scans plays a crucial role in determining pregnancy outcomes.  

This article discusses the optimal amniotic fluid index (AFI) that should be there for a healthy pregnancy while delving into the reasons for low or high AFI.

What is the Amniotic Fluid Index (AFI) in pregnancy?

During pregnancy, the amniotic sac is home to the growing baby, and the amniotic fluid is the protecting and supporting cushion for the baby. The AFI meaning in pregnancy is Amniotic Fluid Index– a standardised measuring criteria to assess the amniotic fluid level in the amniotic sac. 

A decrease or increase in the optimum amniotic fluid index can indicate possible problems or issues in pregnancy, such as 

  • Oligohydramnios or low AFI and 
  • Polyhydramnios or excess AFI 

AFI score is the quantity of amniotic fluid present at a particular stage of pregnancy. The scoring is done with the assistance of ultrasonography. 

The AFI score can be determined by one of the following methods.

  • A four-quadrant technique, where the uterus is demarcated into four separate quadrants and the deepest, uninterrupted, vertical length in each quadrant is measured and added to calculate the median AFI. 
  • The second method is a single deepest pocket technique, where the deepest vertical length of the amniotic sac is measured and expressed in centimetres (cm). This method is commonly used in scans below 24 weeks of pregnancy.   

What are the normal AFI ranges? 

According to the American Pregnancy Association, the amniotic fluid measure increases from the beginning of the third trimester and reaches a peak by 34 to 36 weeks, after which the amniotic fluid level decreases gradually until childbirth. 

Until the first 14 weeks of pregnancy, the amniotic fluid passes through the mother’s circulatory system into the amniotic sac. The baby takes in the amniotic fluid in the early second trimester and begins to excrete it through the kidneys as urine. 

In short, the baby after 14 weeks of pregnancy, recycles the entire volume of the fluid. And so, foetal growth and system development play a crucial role in maintaining the required amniotic fluid levels. Any changes or problems in the system can result in low or high amniotic fluid levels.

The radiologists measure the deepest pockets of amniotic fluids in the four quadrants of the uterus. And the normal measure must be between 5 to 25 cm of AFI.  

  • An AFI < 5-6 is considered oligohydramnios. However, the exact AFI can differ with the gestational age. The exact number can vary by gestational age.
  • And AFI > 24-25 is considered polyhydramnios.

What do you mean by Low AFI?

Low AFI for Oligohydramnios is a condition caused in cases of lower than normal amniotic fluid. Although amniotic fluid levels can be measured by different methods the most common methodology is deep pocket measurement. 

AFI, lower than 5 cm, or if the fluid measurement is less than 500 ml at 32-36 week pregnancy, is referred to as Low AFI or Oligohydramnios. According to statistical data, almost 8% of pregnant women can have low AFI. And majorly diagnosed in the later pregnancy stages, particularly in the third trimester. 

A woman past her due date by a couple of weeks can have a risk of having low AFI, as the AFI levels decrease by nearly 50% by 42 weeks of pregnancy. The other situations that may indicate a low AFI include:

  • Leaking amniotic fluid, 
  • Small babies,
  • Decreased feeling of baby’s movements,
  • Birth defects or developmental delay,
  • Certain pregnancy complications. 

What causes Low AFI in pregnancy?

Some of the possible causes of a low amniotic fluid index can be:

  • Developmental issues in the foetus: Problems with foetal development, such as the development of kidneys or urinary tract can lead to decreased urine production and low amniotic fluid levels.
  • Problems with the placenta: The baby can stop recycling the amniotic fluid in cases of p obstructed blood and nutrient passage to the baby through the placenta.
  • Leaking amniotic sac or membrane: Leaking of amniotic fluid can be like a fast liquid flow or constant dribbling. This leaking can be due to a tear or premature rupture of the membranes (PROM).
  • Pregnancy extending beyond the due date: Pregnancy beyond 42 weeks of gestation can lead to decreased amniotic fluid index. 
  • Pregnancy complications: Pregnancy problems, such as high blood pressure, preeclampsia, gestational diabetes, dehydration, and autoimmune conditions- lupus, can cause low AFI. 
  • Smaller babies: Babies measuring small for a particular stage of pregnancy can produce less urine and lead to low AFI levels. 
  • Multiple pregnancies: Caring for twins or triplets can increase the risk of low amniotic fluid scores. Some can also have twin-to-twin transfusion syndrome, where one twin will have a low AFI level while the other will have too much amniotic fluid. 

What are the risks associated with low amniotic fluid levels in pregnancy?

Low amniotic fluids in the third trimester, usually cause no significant risks or complications. However, very low amniotic fluid levels can lead to certain risks as the umbilical cord can get pressed, and the baby does not get enough nutrients and oxygen.

Some of the pregnancy complications or interventions in labour due to low amniotic fluids are:  

  • Induction of labour artificially, 
  • Delivery through C-section,
  • Babies born with low Apgar scores (lower than 7, requiring medical attention)
  • Babies requiring NICU 

Though it is uncommon for low amniotic fluid levels in the first and second trimester of pregnancy, It can lead to:

  • Miscarriage or pregnancy loss, 
  • Premature delivery,
  • Congenital malformations, or
  • Stillbirth

What are the possible treatments for a Low AFI or Oligohydramnios?

Low amniotic fluid levels in pregnancy call for continuous care and monitoring throughout the pregnancy to ensure that the baby is growing normally. Some of the additional pregnancy care for low AFI include:

  • Additional monitoring: Pregnancies with low AFI will have frequent ultrasound scans, doppler tests, and bio-physical evaluations. However, the mother also needs to note the baby’s movements and inform the doctor in case of the baby’s inactivity or decreased activity. 
  • Amnioinfusion: It is a procedure to infuse the lost amniotic fluid with a saline solution that ensures normal growth and support for the baby until birth. 
  • Hydration: Maternal dehydration can lead to low fluid levels in the womb. Drinking plenty of water can help replenish the amniotic fluid levels during pregnancy. 
  • Labour Induction: If the pregnancy is near its due date and the doctor is suspecting possible pregnancy complications, labour can be induced at an early stage.
  • Caesarean delivery: Sometimes, to avoid possible pregnancy complications or if the baby cannot be out through normal labour, a C-section can be an option for delivery.  

Frequently Asked Questions

  • Can a baby survive with low amniotic fluid?

Yes, a baby is likely to be born healthy and happy, even in pregnancies having low amniotic fluids. Low AFI may be a critical condition, but it is highly treatable in most cases. It is advisable to visit your doctor and follow their instructions to avoid any complications.

  • How common is low AFI in pregnant women?

Low amniotic fluid levels are more common during the last trimester, and according to statistical data, nearly 8% of pregnancy cases are with low amniotic fluid levels.

  • Can amnioinfusion replace amniotic fluid?

Amnioinfusion may not replace the amniotic fluid, but it is a procedure where a saline solution is infused in place of the lost amniotic fluid. The saline solution reduces the risk to the baby while protecting and supporting its development.


Amniotic fluids are vital in a pregnancy that support the baby’s growth and development while cushioning and protecting it. Maintaining the Amniotic Fluid Index (AFI) at optimum ranges is also essential. 

Low amniotic fluid or oligohydramnios, usually detected through ultrasonography, can indicate a potentially serious condition. It can lead to pregnancy complications during pregnancy and impact foetal growth. 

However, Low AFI is a treatable condition, and many pregnant women with low AFI have had healthy babies. Your doctor will monitor and treat this condition according to prenatal scans and pregnancy symptoms while helping you sail through a safe pregnancy. 

Srujana Mohanty
She is the Managing Editor of Cogito137, one of India’s leading student-run science communication magazines. She's been working in scientific and medical writing and editing since 2018, also associated with the quality assurance team of scientific journal editing. Majored in Chemistry with a minor in Biology at IISER Kolkata, Srujana loves doodling and watching series.


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