Fetal serum β2-microglobulin before and after bladder shunting:: A 2-step approach to evaluate fetuses with lower urinary tract obstruction

Purpose: The evaluation of renal function in fetuses with lower urinary tract obstruction by analysis of electrolytes and beta 2-microglobulin in fetal urine has limitations. We measured fetal serum beta 2-microglobulin before and after bladder shunting to evaluate renal function. Materials and Methods: A total of 12 fetuses with lower urinary tract obstruction underwent vesicoamniotic shunting. In addition to the standard evaluation of urinary electrolytes and beta 2-microglobulin, fetal renal status was assessed by pre-shunt and post-shunt fetal serum beta 2-microglobulin. Results: At 2 to 4 weeks after shunting 2 of the 12 fetuses had persistent oligohydramnios, demonstrated increased values of serum beta 2-microglobulin and were confirmed to have renal dysplasia. In the remaining 10 fetuses there was reaccumulation of amniotic fluid for a minimum of 4 weeks after shunting. Serum beta 2-microglobulin values increased after shunting in 4 fetuses, all of which developed renal failure, whereas serum beta 2-microglobulin did not change or was decreased after shunting in 6, of which 4 had normal renal function at latest followup. Conclusions: Urinary electrolytes, urinary beta 2-microglobulin and pre-shunt serum beta 2-microglobulin, whether increased or normal, failed to be predictive of potential response to prenatal intervention. Serial samples of fetal blood may provide distinction between patients who do and do not respond to prenatal treatment of lower urinary tract obstruction.