SERUM BETA(2)-MICROGLOBULIN IN FETUSES WITH URINARY-TRACT ANOMALIES

OBJECTIVE: Our purpose was to establish a reference range of fetal ser um beta(2)-microglobulin, an index of glomerular filtration rate, and to compare the values obtained in fetuses with urinary tract anomalies with this range. STUDY DESIGN: Serum beta(2)-microglobulin was measur ed in 53 control fetuses at 18 to 39 weeks' gestation and in 14 fetuse s with urinary tract anomalies, 9 of which had simultaneous urine samp ling. RESULTS: In controls fetal serum beta(2)-microglobulin had a mea n value of 3.4 mg/L (95% data intervals 2.0 to 4.9) and did not correl ate with gestational age. In the 14 fetuses with urinary tract anomali es beta(2)-microglobulin levels were increased overall compared with c ontrols (median Z score 1.7, range -0.1 to 9.2), and this was also the case in the five fetuses with unilateral renal disorders (median Z sc ore 1.7, range -0.1 to 3.8) and in a fetus who underwent vesicoamnioti c shunting and had normal renal function at birth. Serum beta(2)-micro globulin was normal in 4 fetuses with bilateral urinary tract obstruct ion and normal function at postnatal follow-up and also in 1 of 5 fetu ses with renal failure. In fetuses with bilateral uropathy urinary sod ium correlated with serum beta(2)-microglobulin levels. CONCLUSIONS: I ncreased values of serum beta(2)-microglobulin in fetuses with urinary tract anomalies indicate an impaired glomerular filtration rate. The finding of raised concentrations in fetuses with unilateral damage sug gests that the compensatory role of the normal kidney is not complete during intrauterine life. Larger series are required to ascertain whet her fetal blood sampling is warranted in the antenatal investigation o f renal function, especially in view of the close correlation between urinary sodium and serum beta(2)-microglobulin levels in fetuses with bilateral obstruction.