Transvaginal sonographic assessment of the fetal urinary tract in early pregnancy.

Fetal renal size in the first trimester and the early second trimester of pregnancy was evaluated by high-frequency transvaginal sonography in 537 singleton fetuses at risk for cytogenetic abnormality but not at risk for congenital kidney disease. The percentage of visualization of both kidneys and bladder at different menstrual ages (11-16 weeks) is presented, and centile reference charts for evaluating kidney growth have been compiled. All kidney measurements were found to increase as pregnancy progressed. At 13 weeks, fetal kidneys and fetal urinary bladder were visualized in 92% of the cases screened. The incidence of pyelectasis was high in our population (4.5%), and this pathology was studied by other sonographic scans during pregnancy and postnatally. All fetuses had normal karyotypes. The results presented provide a reference for the assessment of normal renal morphology and growth in early pregnancy.