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Amniotic fluid index

The Amniotic Fluid Index (AFI) is a standardized, noninvasive sonographic technique used to semiquantitatively estimate the volume of amniotic fluid in the pregnant uterus, providing a key assessment of fetal well-being and development.^[1] Introduced in the early 1980s, the AFI measurement divides the maternal abdomen into four equal quadrants using the umbilicus and linea nigra as reference lines, with a transducer placed perpendicular to the skin to identify the largest vertical pocket of amniotic fluid in each quadrant—ensuring no fetal extremities, cord, or placenta are included—before summing these depths in centimeters to yield the index.^[2]^[1] In singleton pregnancies after 20 weeks' gestation, normal AFI values typically range from 5 to 24 cm, peaking around 34–36 weeks before gradually declining toward term, while values below 5 cm indicate oligohydramnios and those above 24 cm suggest polyhydramnios, each associated with distinct risks such as fetal growth restriction, pulmonary hypoplasia, or preterm labor.^[1]^[3] Clinically, AFI is routinely incorporated into the fetal biophysical profile and is indicated for high-risk pregnancies involving conditions like maternal hypertension, diabetes, or intrauterine growth restriction, as well as for evaluating discrepancies in fundal height or suspected membrane rupture, helping guide interventions to mitigate perinatal complications.^[1]

Overview

Definition

The amniotic fluid index (AFI) is a semi-quantitative ultrasound-based assessment of amniotic fluid volume within the uterus during pregnancy, providing an estimate of the fluid surrounding the fetus.^[4] While AFI is widely used, alternative methods such as the single deepest vertical pocket are also employed and may be preferred in certain contexts to reduce false positives for low amniotic fluid.^[5] This measurement helps clinicians monitor hydration status and potential complications related to fluid levels, which can influence fetal health outcomes.^[6] Introduced by Phelan et al. in 1987, the AFI was developed to standardize the evaluation of amniotic fluid, addressing inconsistencies in prior qualitative methods like subjective assessments or single-pocket measurements.^[4] Prior to this, amniotic fluid volume was often gauged imprecisely, but the AFI offered a reproducible technique that correlated with perinatal risks, such as those associated with oligohydramnios or polyhydramnios.^[7] The primary purpose of the AFI is to gauge fetal well-being by approximating amniotic fluid volume, which serves essential roles in pregnancy, including cushioning the fetus against trauma, facilitating limb movement and musculoskeletal development, and promoting lung maturation through fluid inhalation and excretion cycles.^[8] Abnormal AFI values can signal underlying issues affecting these protective and developmental functions.^[9] Fundamentally, the AFI comprises the sum of the deepest vertical measurements of amniotic fluid pockets in each of the four imaginary uterine quadrants—divided by a vertical midline and a horizontal line at the umbilicus—yielding a single composite value in centimeters.^[4] This approach simplifies the quantification process while capturing a representative overall fluid distribution.

Physiological role

Amniotic fluid consists primarily of water, accounting for about 98% of its volume, with the remaining 2% comprising electrolytes, proteins, carbohydrates, lipids, hormones, steroids, and various fetal-derived cells such as those exfoliated from the skin, respiratory tract, urinary system, gastrointestinal tract, and immune cells.^[10] These components create a dynamic, nutrient-rich environment that supports fetal homeostasis and development. The fluid plays critical protective and developmental roles throughout gestation. It acts as a mechanical buffer, shielding the fetus from external trauma and preventing umbilical cord compression to maintain fetal circulation.^[8] Additionally, it stabilizes fetal body temperature by insulating against fluctuations in the maternal environment. Amniotic fluid enables unrestricted fetal movement, which is essential for musculoskeletal development through the mechanical stresses generated by limb motion and positioning.^[11] Furthermore, fetal breathing movements draw the fluid into and out of the lungs, stimulating pulmonary tissue expansion and contributing to lung maturation.^[12] Sources of amniotic fluid shift during pregnancy to meet evolving fetal needs. In early gestation, before 16 weeks, it derives mainly from transudation of maternal plasma across the fetal skin and amnion, functioning as an ultrafiltrate of maternal serum.^[13] Thereafter, fetal urine becomes the dominant source, producing 800–1200 mL daily by term and supplemented by tracheal and lung secretions, while maternal contributions diminish. Regulation occurs via a precise balance of input and output: production from fetal kidneys and lungs is counteracted by fetal swallowing (up to several hundred mL daily), gastrointestinal tract absorption, and intramembranous absorption directly into fetal blood vessels across the amnion.^[14] Volume dynamics reflect this regulatory equilibrium, with amniotic fluid increasing from approximately 50 mL at 12 weeks to a peak of 800–1000 mL between 34 and 36 weeks before a modest decline toward term. This progression supports progressive fetal growth and organ maturation, with the amniotic fluid index providing a quantitative measure of these changes in clinical practice.^[15]

Measurement Methods

Amniotic fluid index technique

The amniotic fluid index (AFI) is a semiquantitative ultrasound technique developed to estimate amniotic fluid volume by assessing the deepest vertical pockets of fluid across four uterine quadrants. Introduced in the 1980s, this method provides a standardized approach for evaluating fetal well-being during routine prenatal sonography.^[16] The procedure requires transabdominal ultrasound equipment, typically a real-time machine equipped with a curvilinear transducer operating at frequencies of 3 to 5 MHz to ensure adequate penetration for imaging the gravid uterus. It is generally performed in singleton pregnancies after 20 weeks gestation, when amniotic fluid dynamics become more reliable for assessment. The patient is positioned supine or in a semi-recumbent state, often with a slight left lateral tilt using a rolled towel under the right hip to optimize venous return and minimize compression of the inferior vena cava.^[1]^[17]^[1] To begin, the sonographer divides the uterus into four equal quadrants using anatomical landmarks: the midline (linea nigra) separates the left and right sides, while a transverse line through the umbilicus delineates the upper and lower portions, resulting in right upper, left upper, right lower, and left lower quadrants. The transducer is oriented in the sagittal plane along the patient's longitudinal axis and held perpendicular to the floor to obtain true vertical measurements, avoiding oblique angles that could distort depths.^[18]^[19] For each quadrant, the sonographer identifies the single deepest vertical pocket of amniotic fluid, ensuring it is unobstructed and free of fetal extremities, umbilical cord, or placental tissue—color Doppler may be used to confirm the absence of cord vessels if needed. The pocket must measure at least 1 cm in horizontal width to qualify as a true fluid space. The depth is then measured vertically from the inner edge of one uterine wall to the inner edge of the opposite wall using electronic calipers, recorded in centimeters. This process is repeated for all four quadrants.^[1]^[19]^[18] The AFI is calculated by summing these four measurements:

\text{AFI} = D_1 + D_2 + D_3 + D_4

where D_i represents the vertical depth of the fluid pocket in each respective quadrant, yielding a total value in centimeters. This summation provides an overall index rather than a direct volumetric measurement.^[1]^[16] Despite its widespread use, the AFI technique is inherently semi-quantitative and subject to interobserver and intraobserver variability due to differences in pocket identification and transducer angulation. It may overestimate oligohydramnios in cases with uneven fluid distribution and is not suitable for precise amniotic fluid volume calculation, as it correlates only moderately with actual volumes determined by more invasive methods like dye dilution. Additionally, technical challenges arise in multiple gestations or with maternal obesity, potentially affecting accuracy.^[1]^[19]

Alternative methods

The single deepest vertical pocket (SDP), also referred to as the maximum vertical pocket (MVP), is a widely used ultrasound-based alternative to the amniotic fluid index (AFI) for assessing amniotic fluid volume. This method involves measuring the vertical depth of the largest cord-free amniotic fluid pocket, which must be at least 1 cm in horizontal dimension to ensure it represents a true fluid collection without fetal parts or umbilical cord. The vertical depth is measured from the near to the far wall. A normal SDP measures between 2 and 8 cm, with values below 2 cm indicating oligohydramnios and above 8 cm suggesting polyhydramnios.^[1] ^[20] Compared to the AFI, the SDP offers several advantages, including lower interobserver variability, stronger correlation with actual amniotic fluid volume, and reduced rates of false-positive diagnoses for oligohydramnios, which can lead to unnecessary interventions. Clinical studies and meta-analyses have demonstrated that the SDP is more accurate in predicting perinatal outcomes, such as adverse neonatal events, than the AFI. For instance, in evaluating polyhydramnios, an SDP greater than 8 cm aligns more reliably with clinical risks than an AFI exceeding 25 cm. The American College of Obstetricians and Gynecologists (ACOG) recommends the SDP as a reliable method for confirming adequate amniotic fluid, particularly in antenatal surveillance, with a depth greater than 2 cm considered reassuring.^[21]^[22]^[23]^[24] Other alternative approaches include the two-diameter pocket (TDP) method, which calculates amniotic fluid volume by multiplying the two largest perpendicular diameters of the deepest fluid pocket, providing a semi-quantitative estimate that some studies suggest improves accuracy over the AFI in detecting oligohydramnios. Additionally, three-dimensional (3D) ultrasound techniques enable direct volumetric estimation of amniotic fluid by reconstructing and summing multiple fluid pocket volumes, offering higher precision than two-dimensional methods but remaining less commonly used due to increased technical complexity, longer scan times, and equipment requirements.^[25]^[26]^[27]^[28] The SDP is particularly preferred in scenarios such as maternal obesity, where ultrasound visualization may be challenging, or when AFI results are borderline, as it minimizes subjective errors and supports more targeted clinical decision-making.^[21]

Reference Values

Normal ranges

The amniotic fluid index (AFI) in normal singleton pregnancies exhibits distinct gestational age-dependent variations, increasing progressively from the mid-second trimester, peaking in the early third trimester, and then declining toward term. A seminal prospective study of 791 uncomplicated pregnancies established nomograms showing a mean AFI of approximately 14 cm at 20 weeks' gestation, rising to a peak mean of 14.6 cm around 28 weeks, and falling to a mean of 12.3 cm by 40 weeks.^[29] More recent nomograms, such as those developed for the United States population, confirm similar trends with mean AFI values peaking around 14-16 cm in the third trimester.^[30] These trends reflect the balance between fetal urine production, swallowing, and other fluid dynamics, with overall amniotic fluid volume stabilizing before a late-gestation reduction.^[9] Statistical norms for AFI are typically defined by the 5th to 95th percentiles from large cohort data, providing gestational age-specific reference ranges. For instance, at 30 weeks, the mean AFI is 14.5 cm, with a normal range of 9.0 to 23.4 cm; in the broader third trimester (28-36 weeks), values between 8 and 18 cm are commonly considered within normal limits based on median observations.^[29]^[3] At term (37-40 weeks), the range narrows to approximately 7.1 to 21.4 cm, emphasizing the need for age-adjusted interpretation to avoid misclassification.^[29] Several physiological factors influence AFI values within normal pregnancies. In twin gestations, the AFI measured in each amniotic sac is comparable to singleton values but tends to be slightly lower on average, though the difference is not statistically significant and total fluid volume across sacs may be equivalent or greater.^[31] Maternal hydration status can transiently elevate AFI, with studies showing increases in women with decreased baseline levels.^[32] Due to inherent measurement variability, AFI assessments show day-to-day fluctuations of up to 2-3 cm, influenced by fetal position, maternal activity, and observer technique; intraobserver variability averages a coefficient of 10.8%, underscoring the value of serial measurements to track trends rather than relying on isolated values.^[33]

Abnormal thresholds

Oligohydramnios is diagnosed when the amniotic fluid index (AFI) measures less than 5 cm or falls below the 5th percentile for gestational age.^[34]^[3] Severe oligohydramnios is indicated by an AFI less than 2 cm. Borderline oligohydramnios, often defined as an AFI between 5 and 8 cm, carries an increased risk of progression to frank oligohydramnios and warrants serial ultrasound monitoring.^[35] Polyhydramnios is identified when the AFI exceeds 25 cm or surpasses the 95th percentile for gestational age, according to guidelines from the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG).^[36] The Society for Maternal-Fetal Medicine (SMFM) uses a slightly lower cutoff of AFI ≥24 cm for diagnosis.^[37] Mild polyhydramnios typically ranges from 25 to 30 cm, while severe cases exceed 30 cm, as outlined in American College of Obstetricians and Gynecologists (ACOG) recommendations for antenatal surveillance.^[38] Borderline polyhydramnios, around 24 to 25 cm, also requires ongoing monitoring due to potential progression.^[39] Thresholds for abnormal AFI are adjusted for gestational age, as amniotic fluid volume peaks around 28 to 34 weeks and declines thereafter; for instance, an AFI below 5 cm after 40 weeks' gestation is particularly concerning due to the naturally lower baseline volumes near term.^[3] Consensus guidelines from ACOG, SMFM, and ISUOG emphasize the single deepest pocket (SDP) as an alternative metric, with SDP less than 2 cm equivalent to oligohydramnios on AFI and SDP greater than 8 cm indicating polyhydramnios.^[38]^[36]

Etiology

Causes of low AFI

Low amniotic fluid index (AFI), also known as oligohydramnios, refers to a reduction in amniotic fluid volume below expected levels for gestational age, typically defined as an AFI of 5 cm or less. This condition affects approximately 4% to 8% of pregnancies, with early-onset cases (before 25 weeks) more commonly linked to congenital anomalies and late-onset cases (after 36 weeks) frequently associated with premature rupture of membranes.^[40] The etiology involves disruptions in fluid production, absorption, or leakage, primarily driven by fetal urine output, placental function, and membrane integrity.^[34]

Fetal Causes

Fetal factors account for a significant portion of oligohydramnios, particularly when urine production—the main source of amniotic fluid—is impaired. Renal anomalies, such as bilateral renal agenesis (Potter sequence) or obstructive uropathy (e.g., posterior urethral valves), prevent fetal urination and lead to anhydramnios or severe oligohydramnios.^[41] Chromosomal abnormalities, including trisomy 18 (Edwards syndrome) or trisomy 13 (Patau syndrome), are associated with structural defects that reduce fluid volume, often detected via prenatal genetic testing.^[34] Additionally, intrauterine growth restriction (IUGR) diminishes fetal urine output due to compromised renal perfusion, exacerbating low AFI.^[42] Congenital infections, such as cytomegalovirus or parvovirus B19, can also contribute by causing fetal anemia or organ damage that indirectly lowers fluid levels.^[42]

Maternal Causes

Maternal conditions can indirectly reduce amniotic fluid by affecting uteroplacental perfusion or fetal kidney function. Dehydration, often from inadequate fluid intake or conditions like hyperemesis gravidarum, decreases maternal blood volume and subsequently reduces fetal urine production.^[43] Hypertensive disorders, including preeclampsia, impair placental blood flow, leading to oligohydramnios.^[44] Certain medications further contribute: angiotensin-converting enzyme (ACE) inhibitors (e.g., enalapril) disrupt fetal renal development and reduce glomerular filtration, while nonsteroidal anti-inflammatory drugs (NSAIDs) like indomethacin inhibit fetal prostaglandin synthesis, thereby decreasing urine output.^[41] These effects are dose-dependent and more pronounced in the third trimester.^[34]

Placental Causes

Placental insufficiency plays a key role in oligohydramnios by limiting nutrient and oxygen delivery, which reduces fetal urine production. Chronic placental abruption, where partial separation occurs without acute hemorrhage, leads to decreased fluid volume through ongoing hypoperfusion.^[45] In multiple gestations, twin-twin transfusion syndrome (TTTS) causes oligohydramnios in the donor twin due to imbalanced blood flow, affecting up to 15% of monochorionic twins.^[41] Uteroplacental insufficiency from chronic hypertension or vascular disease similarly contributes by compromising fetal renal blood flow.^[34]

Other Causes

Premature rupture of membranes (PROM) is the most common cause overall, accounting for 30-40% of third-trimester oligohydramnios cases, as it allows fluid leakage without labor onset.^[34] Post-term pregnancy (beyond 42 weeks) increases risk due to placental senescence and reduced fetal swallowing and urination, with oligohydramnios prevalence rising to over 30% in such cases.^[46] Idiopathic oligohydramnios, without identifiable cause, occurs in about 50% of mild cases and is often transient.^[41]

Causes of high AFI

A high amniotic fluid index (AFI), indicative of polyhydramnios, occurs in approximately 1-2% of pregnancies and results from disruptions in the balance of amniotic fluid production and resorption.^[47]^[48] This excess fluid can stem from various etiologies, broadly categorized by maternal, fetal, placental, and other factors. Maternal causes primarily involve conditions that lead to fetal polyuria through increased glucose load. Uncontrolled gestational diabetes mellitus is a key contributor, as maternal hyperglycemia crosses the placenta, stimulating fetal insulin production and subsequent excessive urine output.^[49] Multiple gestations, such as twins, also elevate risk due to higher cumulative fetal urine production relative to placental clearance capacity.^[50] Fetal causes often relate to impaired swallowing or increased fluid production. Swallowing impairments arise from congenital anomalies, including central nervous system defects like anencephaly or neuromuscular disorders, and gastrointestinal obstructions such as esophageal or duodenal atresia, which prevent normal fluid reabsorption.^[47] High-output states, such as fetal anemia (e.g., from isoimmunization) or fetal tachycardia, promote polyuria by enhancing cardiac output and renal perfusion.^[49] Placental causes are less common but include vascular tumors like chorioangioma, which increase fluid transudation into the amniotic space through abnormal vascularity.^[50] Other causes encompass idiopathic cases, which comprise about 50% of polyhydramnios instances, particularly in mild forms without identifiable anomalies.^[51] Viral infections, such as parvovirus B19, can induce fetal anemia and hydrops, leading to fluid imbalance, while fetal hydrops itself—characterized by widespread edema—further disrupts fluid dynamics.^[49]

Clinical Significance

Risks associated with abnormal AFI

Abnormal amniotic fluid index (AFI) levels, particularly oligohydramnios (AFI ≤5 cm) and polyhydramnios (AFI ≥25 cm), are associated with various immediate and perinatal complications that can affect both fetus and mother.^[34]^[52] Oligohydramnios increases the risk of umbilical cord compression, which can lead to variable decelerations in fetal heart rate and subsequent fetal hypoxia.^[34] In severe cases, especially when diagnosed in the second trimester, it is linked to pulmonary hypoplasia as part of Potter sequence and musculoskeletal deformities due to fetal compression.^[34] These complications contribute to higher rates of neonatal morbidity, including meconium aspiration syndrome and the need for neonatal intensive care unit (NICU) admission.^[34]^[53] Polyhydramnios, on the other hand, heightens the likelihood of preterm labor (relative risk [RR] 1.96, 95% CI 1.35–2.86), placental abruption (RR 3.20, 95% CI 2.20–4.65), and postpartum hemorrhage (RR 1.98, 95% CI 1.22–3.22).^[52] It also predisposes to fetal malpresentation, such as breech position, complicating vaginal delivery.^[41] For the mother, polyhydramnios often causes significant discomfort and dyspnea due to uterine overdistension.^[54] Both conditions share risks such as elevated cesarean delivery rates—approximately twofold higher with oligohydramnios and RR 1.60 (95% CI 1.39–1.84) with polyhydramnios—and increased NICU admissions (RR 1.62, 95% CI 1.11–2.37 for polyhydramnios).^[34]^[52] Perinatal mortality is notably elevated, with low AFI linked to 2- to 4-fold higher rates compared to normal AFI,^[34] and polyhydramnios showing an RR of 4.75 (95% CI 2.67–8.48).^[52] Additionally, if oligohydramnios results from preterm premature rupture of membranes, maternal infection risk rises.^[34] Meta-analyses confirm that an AFI <5 cm is associated with increased rates of adverse perinatal outcomes, including fetal distress and operative interventions, underscoring the need for vigilant monitoring.^[55]^[53]

Prognostic implications

The amniotic fluid index (AFI) serves as a prognostic indicator for fetal and neonatal outcomes, with low AFI values associated with increased risks of intrauterine growth restriction (IUGR) and stillbirth. Specifically, an AFI below 5 cm correlates with a higher incidence of adverse perinatal outcomes in pregnancies complicated by IUGR, with an odds ratio of approximately 2.0 for stillbirth compared to normal AFI levels.^[56] High AFI values, indicative of polyhydramnios, are linked to a 20-40% rate of congenital anomalies, particularly in severe cases where the anomaly prevalence can reach 30-40%.^[57]^[37] Long-term effects of abnormal AFI include renal complications in survivors of oligohydramnios, especially when caused by renal origin, though overall prognosis in such cases can be encouraging with appropriate management. In polyhydramnios associated with aneuploidy or genetic abnormalities, there is an elevated risk of neurodevelopmental disorders and other postnatal issues, such as gastrointestinal atresias.^[58]^[59] Studies indicate that borderline AFI values are not strongly predictive of adverse outcomes when considered in isolation, but their prognostic utility improves when combined with tools such as the biophysical profile.^[60]^[34] Factors modifying prognosis include the gestational age at detection, with earlier onset (e.g., second trimester) worsening outcomes due to risks like pulmonary hypoplasia, and the underlying cause, where congenital anomalies portend poorer results than transient conditions.^[61]^[34] Survival rates vary significantly by severity and timing; severe oligohydramnios diagnosed before 20 weeks is often lethal, with fetal mortality rates of 80-90% due to complications like intrauterine death, whereas cases detected in the third trimester have survival rates up to 85%.^[62]^[34]

Management

Approaches for oligohydramnios

Management of oligohydramnios begins with confirmatory diagnostic monitoring to assess fetal well-being and amniotic fluid status. Serial ultrasound assessments including amniotic fluid index (AFI) measurements are typically performed weekly or twice weekly to track changes in fluid volume.^[63] Non-stress tests (NSTs), biophysical profiles (BPPs), or modified BPPs are recommended weekly or twice weekly upon diagnosis, particularly after 26 weeks gestation, to evaluate fetal heart rate reactivity, movements, tone, breathing, and fluid volume.^[38] Umbilical artery Doppler velocimetry is incorporated if concurrent fetal growth restriction or other complications are present, aiding in the detection of placental insufficiency.^[38] Therapeutic interventions focus on non-invasive measures to potentially increase amniotic fluid volume in isolated cases. Maternal hydration, via oral hypotonic fluids (at least 2 liters daily for 14 days) or intravenous administration (e.g., 1-2 liters of hypotonic solution over 1 day), can temporarily elevate AFI by approximately 20-30% in women with isolated oligohydramnios, with oral approaches often proving more effective than intravenous isotonic fluids.^[64] This strategy is particularly beneficial in idiopathic cases, improving fluid levels without maternal or fetal complications.^[65] For intrapartum management, transcervical or transabdominal amnioinfusion involves infusing warmed saline into the uterine cavity to alleviate umbilical cord compression associated with low fluid, reducing variable fetal heart rate decelerations (relative risk 0.53, 95% CI 0.38-0.74) and operative deliveries (relative risk 0.62, 95% CI 0.46-0.83).^[66] Addressing underlying causes is essential when identifiable, such as discontinuing nonsteroidal anti-inflammatory drugs (NSAIDs), which are avoided after 20 weeks gestation due to their association with reduced amniotic fluid production via fetal renal effects.^[67] In severe cases, particularly before 32 weeks with fetal anomalies or non-reassuring status, early delivery may be indicated after corticosteroid administration for lung maturity.^[34] According to American College of Obstetricians and Gynecologists (ACOG) guidelines, for uncomplicated isolated oligohydramnios, delivery is recommended at 36 0/7 to 37 6/7 weeks gestation; if diagnosed at or beyond 37 weeks, delivery should occur promptly, to mitigate perinatal risks while avoiding unnecessary prematurity.^[68]^[63] Overall outcomes with these approaches show improved perinatal morbidity in monitored and hydrated cases, though persistent severe oligohydramnios may still necessitate individualized timing based on fetal status.^[38]

Approaches for polyhydramnios

Management of polyhydramnios focuses on close monitoring to assess progression and timely interventions to alleviate maternal symptoms such as dyspnea and abdominal discomfort while preventing complications like preterm labor.^[37] For moderate to severe cases, frequent ultrasound examinations, typically every 1-3 weeks, are recommended to evaluate amniotic fluid volume, fetal growth, and cervical length.^[47] In cases associated with suspected fetal anomalies, fetal echocardiography is performed to detect structural heart defects that may contribute to excess fluid.^[37] For pregnancies complicated by maternal diabetes, strict glycemic control through diet, monitoring, and insulin therapy is essential to mitigate further fluid accumulation.^[50] Interventional approaches are reserved for moderate to severe polyhydramnios, defined as an amniotic fluid index (AFI) greater than 30 cm or symptomatic cases. Therapeutic amnioreduction involves ultrasound-guided paracentesis to remove 500-1000 mL of excess fluid, providing symptomatic relief and reducing intrauterine pressure.^[69] This procedure is indicated for severe polyhydramnios causing maternal respiratory compromise or severe discomfort.^[70] Supportive measures include bed rest to alleviate maternal symptoms and tocolytic agents such as nifedipine or magnesium sulfate if preterm labor ensues.^[37] In diabetic patients, optimization of insulin therapy is prioritized to address the underlying etiology. According to the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG), amnioreduction is advised for symptomatic polyhydramnios. The Society for Maternal-Fetal Medicine (SMFM) similarly endorses amnioreduction for severe symptomatic cases, emphasizing multidisciplinary care; for uncomplicated mild polyhydramnios, delivery at 39 weeks or later is recommended (SMFM, 2018).^[39]^[70] Potential complications of interventions include preterm labor, occurring in 10-20% of cases following amnioreduction, as well as infection, placental abruption, and premature rupture of membranes.^[71]

References

[1]
Sonography Evaluation of Amniotic Fluid - StatPearls - NCBI Bookshelf
Jan 22, 2025 · Sonographic evaluation of the amniotic fluid index (AFI) is a standardized and noninvasive method used during pregnancy to assess amniotic fluid volume.Continuing Education Activity · Introduction · Anatomy and Physiology · Indications
[2]
https://pubmed.ncbi.nlm.nih.gov/6385713/
[3]
Amniotic fluid index | Radiology Reference Article | Radiopaedia.org
Aug 5, 2024 · The amniotic fluid index (AFI) is an estimate of the amniotic fluid volume in a pregnant uterus. It is part of the fetal biophysical profile.
[4]
Amniotic fluid index measurements during pregnancy - PubMed
The AFI was determined by the summation of the vertical diameter of the largest pocket in each of the four quadrants. All amniotic fluid studies were conducted ...
[5]
Amniotic Fluid Index - an overview | ScienceDirect Topics
Amniotic fluid index (AFI) is defined as a semiquantitative measure of amniotic fluid volume obtained through ultrasound, where an AFI greater than 5 cm ...
[6]
Amniotic fluid index in low‐risk pregnancy as an admission test to ...
Sep 13, 2002 · Amniotic fluid index (AFI), a semiquantitative ultrasound measure used to denote the volume of amniotic fluid, was first described in 1987 by ...
[7]
Embryology, Amniotic Fluid - StatPearls - NCBI Bookshelf
It provides the necessary fluid, space, and growth factors to allow normal development and growth of fetal organs such as the musculoskeletal system, ...Introduction · Development · Pathophysiology · Clinical Significance
[8]
Amniotic Fluid: Physiology and Assessment | GLOWM
Amniotic fluid is vital to the well-being of the fetus. It cushions the fetus from injury, helps prevent compression of the umbilical cord, and allows room ...Amniotic Fluid: Physiology... · Polyhydramnios · Oligohydramnios
[9]
Amniotic Fluid: A Perspective on Promising Advances in ... - Frontiers
MINI REVIEW article. Front. Pediatr., 13 March 2022. Sec. Neonatology. Volume ... composition of physiological AF. We have highlighted the most important ...
[10]
Amniotic Membrane: Anatomy, Function & Conditions
Oct 30, 2024 · The fluid inside the amniotic sac helps regulate the fetus's temperature. It also helps them move freely, which is essential for musculoskeletal ...
[11]
Physiological factors in fetal lung growth
(c) Fetal breathing movements of normal incidence and amplitude: fetal breathing movements stimulate lung growth, possibly by stretching the pulmonary tissue, ...
[12]
Amniotic Fluid - an overview | ScienceDirect Topics
In early pregnancy amniotic fluid is predominantly an ultrafiltrate of maternal serum. Later in pregnancy, however, fetal urine is the principal constituent.
[13]
Regulation of amniotic fluid volume - PubMed Central - NIH
AFV is determined primarily by the rate of intramembranous absorption (IMA) of amniotic fluid across the amnion and into fetal blood.Missing: "review | Show results with:"review
[14]
Amniotic fluid volume dynamics | Fetal and Maternal Medicine Review
Oct 10, 2008 · While the fetus is producing large volumes of urine, the volume of amniotic fluid is normally maintained within a very narrow range. Deviations ...
[15]
The Four-Quadrant Assessment of Amniotic Fluid Volume
Amniotic fluid volume assessment using a semiquantitative four-quadrant technique, the amniotic fluid index, was evaluated in relationship to fetal heart ...
[16]
Basic Obstetric Ultrasound - Medscape Reference
Oct 17, 2024 · Modern equipment typically includes a transabdominal transducer with 3 to 5 MHz frequency and a transvaginal transducer with 5-10 MHz frequency.<|separator|>
[17]
Amniotic Fluid Index (AFI)
### Amniotic Fluid Index (AFI) Measurement Procedure Summary
[18]
[PDF] AMNIOTIC FLUID ASSESSMENT
The amniotic fluid index (AFI) technique is based on the division of the uterus into. 4 equal quadrants and measuring the deepest vertical pocket of fluid in ...
[19]
https://www.glowm.com/pdf/ultrasound_in_obstetrics_and_gynecology-chapter9.pdf
[20]
Amniotic fluid volume: When and how to take action
Jun 1, 2014 · Amniotic fluid index (AFI) and single deepest pocket (SDP) are the most-used semi-quantitative techniques. Color Doppler U/S does not improve ...
[21]
Antepartum Fetal Surveillance - Obstetrics & Gynecology
Determination of the amniotic fluid volume––a single deepest vertical pocket greater than 2 cm is considered evidence of adequate amniotic fluid (38–40). Each ...
[22]
Two diameter pocket method | Radiology Reference Article
Sep 26, 2021 · The two diameter pocket (TDP) method is an alternative method of assessing amniotic fluid volumes on ultrasound.
[23]
The amniotic fluid index, single deepest pocket, and two ... - PubMed
This study was undertaken to determine normative values for amniotic fluid index, single deepest pocket, and 2-diameter pocket across gestation.
[24]
Amniotic fluid volumetry by three-dimensional ultrasonography ...
We conclude that there was an increase in AFV assessed by 3D-US. The AFV values for normal fetuses can be used for comparison with those detected in pregnancies ...Missing: estimation | Show results with:estimation
[25]
The amniotic fluid index in normal human pregnancy - PubMed
In term pregnancies, the boundaries of the amniotic fluid index were 115 mm (mean), 68 to 196 mm (5th to 95th percentiles). In postdates pregnancies greater ...
[26]
The amniotic fluid index in normal twin pregnancies - PubMed
Conclusion: Individual amniotic fluid indices can be obtained in twin pregnancies, and the values are comparable with those of singleton gestations.
[27]
Maternal hydration increases amniotic fluid index - PubMed
These findings suggest that maternal oral hydration increases AF volume in women with decreased fluid levels.
[28]
Relationship of amniotic fluid index (AFI) in third trimester with fetal ...
Aug 12, 2016 · It was suggested that the differences in hormonal environment between female and male fetuses may be the reason for the correlation of AF ...
[29]
Intraobserver and interobserver variability of the amniotic fluid index
Results: Overall, the coefficient of variation for amniotic fluid index measurements varied from 10.8% within examiners to 15.4% between examiners. Both ...
[30]
Oligohydramnios - StatPearls - NCBI Bookshelf
May 4, 2025 · Amniotic fluid is best evaluated by 2 methods: 1) by measuring the single DVP of amniotic fluid (sometimes called the MVP or SDP) or 2) by ...Oligohydramnios · Evaluation · Treatment / ManagementMissing: alternative | Show results with:alternative
[31]
Clinical significance of borderline amniotic fluid index and ... - PubMed
An AFI 5 cm or less was considered oligohydramnios, 5-8 cm was considered borderline, and more than 8 cm to 24 cm was considered normal.
[32]
ISUOG Practice Guidelines (updated): performance of the routine ...
May 20, 2022 · Amniotic fluid index (AFI) may be preferable in assessing polyhydramnios, while deepest vertical pocket (DVP) may be preferable in assessing ...Missing: thresholds | Show results with:thresholds<|control11|><|separator|>
[33]
Polyhydramnios - StatPearls - NCBI Bookshelf - NIH
Nov 9, 2024 · However, more recent data suggest an amniotic fluid index of 24 cm exceeds the 97.5th percentile at all gestational ages after 20 weeks. For ...
[34]
Indications for Outpatient Antenatal Fetal Surveillance | ACOG
The purpose of this Committee Opinion is to offer guidance about indications for and timing and frequency of antenatal fetal surveillance in the outpatient ...
[35]
Polyhydramnios - ISUOG
An AFI over 24 cm is considered polyhydramnios. Mild polyhydramnios is the most common and often resolves on its own. Moderate or severe polyhydramnios may ...Missing: oligohydramnios | Show results with:oligohydramnios
[36]
Prevalence Rate, Probable Causes, and Perinatal Outcomes ... - NIH
May 29, 2024 · The oligohydramnios risk factors are premature rupture of membranes, intrauterine growth restriction, and birth defects [29]. Oligohydramnios, ...
[37]
Polyhydramnios and Oligohydramnios - Medscape Reference
Jun 25, 2025 · Causes of oligohydramnios include the following: Fetal urinary tract anomalies, such as renal agenesis, polycystic kidneys, or any urinary ...Etiology · Prognosis · Morbidity/mortality
[38]
Amniotic Fluid Disorders: From Prenatal Management to Neonatal ...
Mar 16, 2023 · The amniotic fluid protects the fetus from trauma and infection and helps regulate fetal body temperature. It allows fetal movements, and thus ...Missing: maturation | Show results with:maturation
[39]
Oligohydramnios: Causes, Symptoms, Diagnosis & Prevention
Low amniotic fluid affects about 4% of women during pregnancy. It's most common in the last three months of pregnancy (third trimester). This rate rises to ...
[40]
Oligohydramnios - Geeky Medics
Sep 14, 2021 · Causes of oligohydramnios · Fetal growth restriction · Maternal medical comorbidities (e.g. hypertension) · Placental abnormalities (e.g. abruption) ...Key Points · Latest Videos · Instrumental Vaginal Birth
[41]
Oligohydramnios - Causes - Treatment - Prognosis - TeachMeObGyn
The most common causes are premature rupture of membranes (often missed by the mother) and placental insufficiency, however structural abnormalities such as ...Aetiology · Clinical Assessment · Management
[42]
Prevalence and associated factors of oligohydramnios in ... - NIH
Aug 2, 2022 · Oligohydramnios occurs in about 1–5% of term pregnancies worldwide; however, the prevalence rises to more than 12% in post-term pregnancies [5–7] ...
[43]
Polyhydramnios - Amniotic fluid - The Fetal Medicine Foundation
Most cases of mild polyhydramnios are idiopathic, but most cases with moderate or severe polyhydramnios are due to maternal or fetal disorders. In most cases, ...
[44]
Isolated polyhydramnios: Is a genetic evaluation of value?
Polyhydramnios is a common complication of pregnancy, with an incidence of 1–2 % in a general obstetric population [1]. The volume of amniotic fluid is the ...
[45]
Polyhydramnios - Gynecology and Obstetrics - Merck Manuals
AFI ≥ 24 cm: AFI is the sum of the vertical depth of fluid measured in each quadrant of the uterus; normal AFI ranges from > 5 to < 24 cm. SDP ≥ 8 cm: SDP is a ...Missing: thresholds | Show results with:thresholds
[46]
Polyhydramnios: Causes, Symptoms, Complications & Treatment
Polyhydramnios is when there is too much amniotic fluid in your uterus during pregnancy. Amniotic fluid surrounds and protects the fetus in your uterus.
[47]
Polyhydramnios - Possible Causes and Next Steps - The ObG Project
Aug 5, 2016 · Measurement ; Severity. Mild AFI: 24.0-29.9 cm or SDP 8-11 cm; Moderate AFI: 30.0-34.0 cm or SDP 12-15 cm; Severe AFI: ≥35 cm or SDP ≥16 cm.Missing: thresholds oligohydramnios
[48]
Obstetric and neonatal outcomes in pregnant women with idiopathic ...
Mar 4, 2024 · This meta-analysis suggests that pregnant women with IP may be at increased risk of perinatal complications and adverse neonatal outcomes.
[49]
Maternal and Perinatal Outcomes in Oligohydramnios - NIH
Feb 18, 2025 · Oligohydramnios is associated with a high rate of operative deliveries, increased neonatal morbidity, and adverse perinatal outcomes.
[50]
Too Much of a Good Thing: Updated Current Management and ...
Nov 30, 2024 · Polyhydramnios is linked to complications such as placental abruption, preterm labor, congenital anomalies, and postpartum hemorrhage.
[51]
https://www.obgproject.com/2016/08/05/polyhydramnios-what-is-it/
[52]
What is the normal range for Amniotic Fluid Index (AFI)? - Dr.Oracle
Oct 24, 2025 · Normal Amniotic Fluid Index (AFI) Range. The normal range for Amniotic ... Increased risk of stillbirth (odds ratio 2.6,95% CI 2.1-3.2) 1 ...
[53]
Background, Causes of Fetal Growth Restriction, Perinatal Implications
Sep 25, 2024 · ... amniotic fluid index (AFI) of less than 5 and 9% with an AFI higher than 5 (odds ratio, 2.13; 95% CI, 1.10-4.16). ... IUGR is intrauterine ...
[54]
Antenatal oligohydramnios of renal origin: long-term outcome
Oct 25, 2006 · ROH is not always associated with a poor prognosis and long-term outcome in survivors is encouraging.
[55]
What to expect after birth in idiopathic polyhydramnios? An analysis ...
Sep 26, 2023 · Particularly high risks include neurodevelopmental disorders, genetic abnormalities, and gastrointestinal atresias. Keywords: Gastrointestinal ...
[56]
Effect of Prenatal Ultrasound Screening on Perinatal Outcome
Sep 16, 1993 · The Routine Antenatal Diagnostic Imaging with Ultrasound (RADIUS) trial was a practice-based, multicenter study of pregnant women at low risk ...<|separator|>
[57]
Oligohydramnios Imaging: Practice Essentials, Workup
Jan 4, 2022 · Oligohydramnios has been defined as an amniotic fluid index (AFI) less than 5 cm, although 8 cm has occasionally been used as a cut-off ...
[58]
Oligohydramnios - Gynecology and Obstetrics - Merck Manuals
If oligohydramnios is suspected, amniotic fluid should be assessed quantitatively using the amniotic fluid index (AFI) or single deepest pocket (SDP). The ...Missing: guidelines | Show results with:guidelines
[59]
An Update on Maternal Hydration Strategies for Amniotic Fluid ...
Maternal hydration increases amniotic fluid index in women with normal amniotic fluid. ... Effect of maternal hydration on the increase of amniotic fluid index.
[60]
The effect of maternal intravenous hydration on amniotic fluid index ...
Mar 7, 2022 · The results of the present study suggested that maternal intravenous hydration significantly increases AFI in women with oligohydramnios.
[61]
Amnioinfusion for potential or suspected umbilical cord compression ...
Amnioinfusion aims to prevent or relieve umbilical cord compression during labour by infusing a solution into the uterine cavity.
[62]
FDA recommends avoiding use of NSAIDs in pregnancy at 20 ...
Oct 16, 2020 · Discontinue the NSAID if oligohydramnios occurs and follow up according to clinical practice. To help FDA track safety issues with medicines ...
[63]
Medically Indicated Late-Preterm and Early-Term Deliveries - ACOG
Deferring delivery to the 39th week is not recommended if there is a medical or obstetric indication for earlier delivery.
[64]
Polyhydramnios - Diagnosis and treatment - Mayo Clinic
Dec 5, 2023 · Or they might measure the fluid in the four quadrants of the uterus, also called the amniotic fluid index (AFI). Polyhydramnios is diagnosed ...Missing: definition | Show results with:definition
[65]
Amnioreduction in the management of polyhydramnios complicating ...
Amnioreduction has a useful role in the management of polyhydramnios in singleton pregnancies. Complications are uncommon, and delivery typically occurs ...
[66]
Balancing Benefits and Risks of Indomethacin in the Management of ...
Jun 28, 2022 · Indomethacin is known to reduce salt wastage and subsequent polyhydramnios during pregnancy; however, it reduces the Ductus Arteriosus diameter among other ...