Two-dimensional and three-dimensional (3D) or four-dimensional (4D) US may elucidate the fetal swallowing mechanism; if this appears abnormal, suspicion of neuromuscular disorder is increased. Based on available data from randomized control trials (RCTs) the American College of Obstetricians and Gynecologists (ACOG) supports the use of the deepest vertical pocket of amniotic fluid volume of 2 cm or less to diagnose oligohydramnios rather than an amniotic fluid index of 5 cm or less . Decreased renal perfusion may be the underlying mechanism for this. Components of a Basic Second-Trimester Ultrasound Examination, Documentation of fetal heart rate and number and lie of fetuses, Location and appearance of the placenta and its relationship to the internal os, Dotun Ogunyemi, Perry Friedman, in Obstetric Imaging: Fetal Diagnosis and Care (Second Edition), 2018. These extremes of AF volume have important clinical implications. the management of a complicated pregnancy. One distinguishing feature of renal agenesis is absence of a bladder.28 Color or power Doppler US can be used to identify the renal arteries, distinguishing kidneys from adrenal glands (see Chapter 11). Imaging is also an important tool for ongoing fetal surveillance. The reports are conflicting but the key points on analysis seem to be: The AFI is more likely to lead to a false-positive diagnosis of oligohydramnios. Such intervention has not shown an overall improvement in perinatal outcome. Christina K H Yu, Sarah Bower, in Twining's Textbook of Fetal Abnormalities (Third Edition), 2015. Amniotic fluid level index (AFI) is used to measure the amniotic levels expressed in centimeters by gestational age. In a study of 220 cases of fetal hydrops, Hartge and coworkers51 analysed the distribution of fluid collections and the gestational age at ultrasound diagnosis in fetuses with different causes (Table 36.7). b. The deepest (maximal) vertical pocket (DVP) depth is considered a reliable method for assessing amniotic fluid volume on ultrasound 1,2.It is performed by assessing a pocket of a maximal depth of amniotic fluid which is free of an umbilical cord and fetal parts.. The normal range for the AFI is 5-25 cms. The diagnosis of oligohydramnios may lead to intervention with acknowledged increased rates of induction of labour and increased Caesarean section rates following on a diagnosis of third trimester oligohydramnios. Duodenal atresia, imperforate anus, choanal atresia, and other gastrointestinal obstructions may manifest with polyhydramnios, along with dilated loops of bowel or the “double bubble” sign in the abdomen, particularly after the second trimester.18 A narrow thorax, especially in conjunction with shortened limbs, may suggest a skeletal dysplasia. c. 20 and 40 cm. 43.2) and was first introduced by Phelan and colleagues in 1987 for term pregnancies.16 This measurement system was subsequently expanded to include second and third trimester pregnancies (16–42 weeks’ gestation),17 and gestation-specific normal ranges for AFI were developed. The width of each measured pocket must be at least 1 cm. By continuing you agree to the use of cookies. Fluctuations outside of this range define oligohydramnios (too little amniotic fluid) or polyhydramnios (too much amniotic fluid). On the basis of multiple reviews it would seem that whilst practitioners do favour the AFI, this method does lead to over-diagnosis of oligohydramnios and an increase in the number of labour inductions and Caesarean deliveries. The normal range for the AFI is 5-25 cms. Oligohydramnios may result from various forms of renal obstruction, and US detects fetal obstructive uropathy with a sensitivity of 95% and specificity of 80%.24 Findings suggestive of obstruction are dilation of the renal pelvis and calyces, increased renal echogenicity, and bladder distention. Another cause of oligohydramnios is premature rupture of the membranes (PROM), which occurs in approximately 10% of all pregnancies and is associated with increased perinatal mortality and morbidity due to premature labour, chronic fetal distress or infection. Amniotic fluid volume is evaluated via AFI or SDP. Polyhydramnios in the setting of a monochorionic multiple gestation raises concern for twin transfusion syndrome, especially if the other fetus has oligohydramnios (Fig. An AFI of more than 20 to 24 centimeters is called polyhydramnios, which means that there is a high amount of amniotic levels present in the mother’s womb. It is a part of the biophysical profile. When obstructive uropathy is suspected, detailed assessment should include evaluation of dilation (hydronephrosis, hydroureter), renal parenchyma (echogenicity), renal size, and bladder size. Amniotic fluid level index (AFI) is used to measure the amniotic levels expressed in centimeters by gestational age. In the fetus with suspected placental insufficiency-related oligohydramnios, especially if growth restriction is also present, Doppler evaluation is indicated (Chapter 110). 70–80%. 3. 5 and 25 cm. An AFI of less than 5 to 6 centimeters leads to a condition called oligohydramnios, which means that amniotic levels are low. In multiple pregnancies, SDP for each fetus is typically reported (Fig. As noted earlier, 4D US imaging allows observation of fetal swallowing, which may suggest a neuromuscular disorder. There is a high association with pulmonary hypoplasia when severe oligohydramnios develops: a. before 20–25 weeks of gestation. Complications associated with oligohydramnios and polyhydramnios are similar and include premature birth and various defects like hypoplastic lungs. Doppler US should be considered in evaluation of a fetus with polyhydramnios. About 40% of cases are unexplained. Fact Check: What Power Does the President Really Have Over State Governors? Amniotic Fluid Index (AFI): this method uses the sum of four of the deepest vertical pocket of fluid. All three methods have similar inaccuracies when used for multiple gestations as for singleton pregnancies. One pitfall in bilateral renal agenesis is that the adrenal glands may assume a discoid shape and move laterally and inferiorly, mimicking kidneys. It is also the preferred method for estimating the amniotic fluid volume in twin pregnancies. Hydrops is only a clinical sign. The fetus may have Potter facies, a “silk stocking effect,” with flattened nose and low-set, flattened, enlarged external auricles.18 There may be positional deformation of the hands and feet with flexion contractures of the elbows, knees, and feet. Anything more than 25 cm is too much amniotic fluid, and anything less than 5 cm during the third trimester is too low. From: Obstetric Imaging: Fetal Diagnosis and Care (Second Edition), 2018, Ross I. To calculate the amniotic fluid index (AFI), the anteroposterior diameters of the largest empty fluid pocket (no umbilical cord or fetal parts) in each quadrant are added together. An AFI of less than 5 to 6 centimeters leads to a condition called oligohydramnios, which means that amniotic levels are low. 119.5). Finally, 3D US imaging may be useful for evaluation of the fetal face, including the mandible in cases of micrognathia. The amniotic fluid measurement is only one part of an assessment with fetal biometry; a detailed anatomical survey and Doppler evaluation are all part of the process of diagnosis of a complicated pregnancy. Amniotic Fluid Index (AFI): this method uses the sum of four of the deepest vertical pocket of fluid. It should be used as part of the clinical evaluation of the patient and involve additional sonographic assessment (e.g., biophysical profile, non-stress test, ultrasound examination for estimated fetal weight, anatomic survey etc) in an appropriate clinical scenario, i.e. In the absence of other findings, fetal anemia should be suspected, and Doppler studies should be done for assessment. CVPS is a clinical tool that accounts for both cardiac function and Doppler velocimetry by calculating the extent of derangement in five parameters: fetal hydrops, heart size, cardiac function and arterial and venous Doppler flow through the umbilical vessels and ductus venosus.50. In clinical practice the measurement of amniotic fluid volume, either the AFI or SDP, is not a measurement that should ever used in isolation. Your doctor will perform an ultrasound to confirm the presence of an excess or lack of amniotic fluid to find out where you rate on the amniotic fluid index (AFI). The placenta may reveal other pathology, such as chorioangioma, which may be associated with polyhydramnios because of increased fetal cardiac output. The normal amniotic fluid index ranges between: a. Oligohydramnios can also accompany premature (before onset of contractions) rupture of the membranes, fetal growth restriction, renal disorders, and chronic disruptions in placental function.