Ultrasound evaluation of hydronephrosis of pregnancy.

Four hundred ninety-two patients, including 449 pregnant patients, 39 nonpregnant control patients, and 4 patients with pelvic masses, had renal ultrasonography using gray scale technique. Measurements of renal pelvic diameters in the normal pregnant patients revealed an overall incidence of 63 percent renal pelvic dilatation over the nonpregnant controls. Maximum normal renal pelvic diameters were 1.1 cm on the right and 0.9 cm on the left. The maximum normal expected renal pelvic diameter (97.5 percent confidence level) in pregnancy is 2.7 cm on the right and 1.8 cm on the left in the last two trimesters of pregnancy. There was no significant difference between primiparous and multiparous patients, but pregnant patients were significantly different from controls in every trimester (p less than 0.01). Maximum dilatation occurred at 24--28 weeks of gestation. The right renal pelvis was enlarged to the greatest degree in 90 percent of normal patients. Patients with pelvic masses showed a similar pattern of right-sided hydronephrosis.