Amniotic fluid index (AFI) is a quantitative estimate of

amniotic fluid The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products betwee ...

and an indicator of

fetal A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal develo ...

well-being. It is a separate measurement from the

biophysical profile A biophysical profile (BPP) is a prenatal ultrasound evaluation of fetal well-being involving a scoring system, with the score being termed Manning's score.

. AFI is the score (expressed in cm) given to the amount of amniotic fluid seen on

ultrasonography Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...

of a pregnant

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

. To determine the AFI, doctors may use a four-quadrant technique, when the deepest, unobstructed, vertical length of each pocket of fluid is measured in each quadrant and then added up to the others, or the so-called "Single Deepest Pocket" technique. An AFI between 8–18 is considered normal. Median AFI level is approximately 14 from week 20 to week 35, when the amniotic fluid begins to reduce in preparation for birth. An AFI < 5–6 is considered as

oligohydramnios Oligohydramnios is a medical condition in pregnancy characterized by a deficiency of amniotic fluid, the fluid that surrounds the fetus in the abdomen, in the amniotic sac. It is typically diagnosed by ultrasound when the amniotic fluid index (A ...

. The exact number can vary by gestational age. The fifth percentile for gestational age is sometimes used as a cutoff value. An AFI > 24–25 is considered as

polyhydramnios Polyhydramnios is a medical condition describing an excess of amniotic fluid in the amniotic sac. It is seen in about 1% of pregnancies. It is typically diagnosed when the amniotic fluid index (AFI) is greater than 24 cm. There are two clin ...

Causes of low amniotic fluid

There are many things that can cause low AFI, these include: * Leaking or rupture of membranes: Leaking or rupture of membranes may be caused by a gush of fluid or a slow constant trickle of fluid. This is due to a tear in the membrane.

Premature Premature may refer to: * ''Premature'' (2014 film), an American comedy film * ''Premature'' (2019 film), an American romantic drama film * ''PREMature'', a 2015 British television drama miniseries See also * Premature aging, of an organism * P ...

rupture of membranes can also result in low amniotic fluid levels. * Placental problems:

Placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...

l problems may cause low amniotic fluid. If the placenta is not providing enough blood and nutrients to the baby, then the baby may stop recycling fluid. * Birth defects:

Birth defects A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...

may occur if the fetus has problems with the development of the

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...

s or

urinary tract The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, con ...

, which could cause little urine production, and it can lead to low levels of amniotic fluid. * Maternal complications: Maternal complications may cause low amniotic fluid. Some factors such as

hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

preeclampsia Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease ...

, and chronic hypoxia in a woman can have an effect on amniotic fluid levels.

References

Tests during pregnancy {{human-repro-stub