Effect of maternal hydration on mild fetal pyelectasis

The aim of our study was to determine whether maternal hydration status prior to prenatal sonography affects fetal renal pelvic diameter. The renal pelvic diameters of fetuses from two different institutions were compared prospectively. At one institution 74 women were asked to drink 32 to 48 ounces of water prior to undergoing sonography (hydration group), whereas at the second institution, no specific hydration regimen was requested of 176 subjects. The inclusion criteria were as follows: greater than 15 weeks' gestation, otherwise normal obstetrical sonogram, normal amniotic fluid volume, and negative family history for renal disease. Renal pelvic diameter, degree of maternal bladder fullness, and gestational age were compared between the two groups using logistic regression analysis and log-linear analysis. A P value < 0.01 was considered significant. Bladder fullness in the two groups differed significantly (P < 0.001). Logistic regression analysis showed a very strong effect of maternal bladder fullness on fetal renal pelvic diameter (P < 0.001). The log-linear analysis model showed a highly significant association between maternal bladder fullness and fetal renal pelvic diameter (P < 0.001). We conclude that maternal hydration influences fetal renal pelvic diameter. The larger fetal renal diameters seen in the hydrated group support physiologic theories that the effects of maternal hydration on amniotic fluid volume are partially mediated via fetal urine production.