Amniotic fluid index and fetal bladder outlet obstruction. Do we really need more?
ABSTRACT With the constant advances in technology and expertise of prenatal diagnosis, necessity of early counseling in cases of bilateral obstructive uropathy has become of paramount importance. To better evaluate fetal renal function new biochemical (serum and urine) fetal markers have been introduced in the literature. However, they are only available at select centers and always requiring an invasive approach. Furthermore, paucity of normal controls sometimes makes interpretation of results difficult. Owing to this growing interest towards biochemical evaluation of fetal renal function, assessment of amniotic fluid, which is mostly expression of fetal urination, has progressively fallen into disrepute, and studies comparing the amount of amniotic fluid with renal function are scant.
In a 3-year period 28 cases of bilateral obstructive uropathy were seen prenatally at the Artemisia Medical Center. All cases were initially reviewed at 17 to 20 weeks of gestation when a distended fetal bladder with thickened wall and enlarged kidneys were visualized. At the same time ultrasonographic assessment of amniotic fluid was performed by calculating the amniotic fluid index. An amniotic fluid index less than the 25th percentile was considered below average and an index less below the 5th percentile was considered oligohydramnios, whereas an index between 50th and 75th percentiles was considered normal. All cases were subsequently evaluated for renal function up to age 1 year. Impaired renal function was defined as a serum creatinine greater than 1.2 mg/dl before age 1 year.
Of the 28 cases 18 had an index of oligohydramnios (group 1) and 10 had a normal index (group 2). No significant variations were observed in amniotic fluid index at repeated consultations throughout pregnancy. Two cases in group 1 and 1 case in group 2 were lost to followup while in the other group 1 cases intrauterine death occurred. Bilateral obstructive uropathy was confirmed in all instances after birth as valves in 18 cases and urethral atresia in 3. Of the 12 surviving group 1 cases there were 3 neonatal deaths from severe lung hypoplasia, and in the remaining 9 cases mean serum creatinine at each evaluation before age 1 year was 1.3 +/- 0.2 mg/dl. All patients in group 2 survived with a mean serum creatinine at each evaluation of 0.6 +/- 0.1 mg/dl (p <0.05).
Despite widespread use of prenatal biochemistry, evaluation of amniotic fluid by the amniotic fluid index remains a reproducible and inexpensive method to predict renal function in cases of bilateral obstructive uropathy of any origin. It retains its validity not only in severe, but also in milder reductions. Conversely, intact amniotic fluid mostly invariably predicts normal renal function at long-term evaluation. For a better understanding of the disease such information is to be promptly conveyed to the prospective parents at each prenatal consultation.
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ABSTRACT: The purpose of this study was to assess the effect, if any, of color Doppler on the measurement of the amniotic fluid index in term pregnancies. It is hypothesized that color Doppler may enhance the detection of oligohydramnios. The amniotic fluid index was performed with and without color Doppler on pregnancies greater than or equal to 36 weeks gestational age. Differences in the mean amniotic fluid index measurements were assessed. The incidence of oligohydramnios was examined using both techniques. Differences in continuous variables were assessed with the paired t test, differences in categorical variables were assessed using the Fisher Exact Test. There were 155 pregnancies examined, the amniotic fluid index was significantly decreased when color Doppler was added to the standard technique. (P < .0001) The incidence of oligohydramnios was higher with the application of color Doppler to the standard amniotic fluid index. (P < .05). Color Doppler results in a significantly lower amniotic fluid volume measurement and may enhance the detection of oligohydramnios.Journal of Perinatal Medicine 01/1999; 27(4):245-9. · 1.95 Impact Factor
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ABSTRACT: Final assessment on the outcome of fetal obstructive uropathy is a challenging matter. Ultrasonography, fetal urine electrolytes, and beta 2 microglobulin are postulated as being useful in many cases. For cases in which renal function remains unclear, ultrasound-guided fetal kidney biopsy may be used in order to detect histologic features distinctive of renal dysplasia. We present preliminary results aimed at studying the feasibility and possible risks. Biopsies were initially performed in 11 severely malformed fetuses, three of them with associated renal abnormalities. The success rate in obtaining renal material was 63.6 per cent with no maternal complications. In the next phase of this study, ten biopsies and urine collections were performed in fetuses with bilateral obstructive uropathy. The success rate was 50 per cent with no complications. Normal fetal renal histology was seen in 80 per cent of cases. In one case, although electrolytes were normal, a histologic diagnosis of renal dysplasia was made, showing a good correlation with outcome. In conclusion, fetal kidney biopsies for obstructive uropathy are feasible and further studies are needed to show their clinical relevance and risks.Prenatal Diagnosis 02/1998; 18(2):101-9. · 2.68 Impact Factor
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ABSTRACT: We evaluated a subset of infants with bilateral markedly hyperechoic "bright" kidneys noted prenatally in association with normal amniotic fluid volume during gestation. Prenatal ultrasound showed increased renal parenchymal echogenicity bilaterally with preservation of the medullary pyramid architecture. These children were followed for up to 3 years to determine potential changes in the sonographic appearance of the echogenic renal parenchyma and to assess renal function. In 3 years 8 cases of bilateral hyperechoic fetal kidneys were identified. During postnatal followup renal echogenicity resolved in 4 cases, diminished in 1 and remained the same in 3. The serum creatinine and electrolytes were normal in all cases followed for more than 3 months. Other renal findings included vesicoureteral reflux in 2 of 7 cases, mild pelvic ectasia in 1 and tiny medullary calcifications in 1. The specific etiology of increased echogenicity is unknown, although 1 infant appeared to have a form of autosomal recessive disease with liver hyperechogenicity as well. We conclude that fetuses with bilateral hyperechoic kidneys associated with normal amniotic fluid volume have a favorable outcome. Ultrasonographic finding of marked parenchymal hyperechogenicity appears to improve with time; in our experience renal function is normal and the infants thrive. Continued followup is necessary to determine the long-term natural history of this phenomenon, as is subsequent prenatal and postnatal evaluation of future siblings to assess genetic risk.The Journal of Urology 03/1995; 153(2):442-4. · 3.70 Impact Factor