Table 1 Summary of the pros and cons of different fetal parameters used to predict postnatal renal function and select candidates for antenatal intervention
From: Antenatal and postnatal management of posterior urethral valves: where do we stand?
Fetal parameters | Pros | Cons |
|---|---|---|
Fetal bladder urinary electrolytes (urinary sodium > 100 mEq/L, chloride > 95 mEq/L, osmolarity > 210 mOsm/L)  Sensitivity 40–100%  Specificity 80% | Have been widely studied | Invasive Repeated sampling is usually required Variable reference ranges Levels vary with gestational age Conflicting data on diagnostic performance |
Fetal urinary ẞ2-mircroglobulin  Sensitivity 57–81%  Specificity 80–89% | Reflect glomerular damage | Invasive Variable reference ranges Levels vary with gestational age |
Fetal serum ẞ2-mircroglobulin | Can be used to reflect the recoverability of fetal renal function following antenatal intervention | Invasive Technically difficult More risky than fetal bladder urine sampling early in pregnancy Variable reference ranges Levels vary with gestational age |
Fetal ultrasound (severity of hydronephrosis, gestational age at diagnosis, cortical echogenicity, cortical cysts, amniotic fluid volume)  Sensitivity 57–66%  Specificity 84–100% | Noninvasive Widely available Sedation is not required Renal cortical appearance is highly predictive of renal dysplasia on autopsy or biopsy and is a good predictor of postnatal renal function | Limited specificity in distinguishing PUV from other causes of fetal lower urinary tract obstruction Results are limited by maternal obesity, fetal movements, oligohydramnios and operator expertise Gestational age at diagnosis, hydronephrosis and megacystis are poor predictors of postnatal renal function Amniotic fluid volume does not reflect renal function in the first trimester Renal parenchymal architecture is difficult to assess early in pregnancy (before 22–23 weeks) |
Fetal MRI | Better anatomic details More reliably distinguish PUV from other causes of fetal obstructive uropathy ADC of the fetal renal parenchyma has been used to predict postnatal renal function | Maternal sedation is sometimes required Performing MRI late in pregnancy limits its value as a predictive tool for antenatal intervention |
Fetal urinary omics  Sensitivity 50–88%  Specificity 68–95% | Better sensitivity and specificity for prediction of postnatal renal insufficiency | Invasive Expensive Still investigational Cutoff values do not exist |