Pregnancy causes definite and marked changes in the urinary tract. The most striking change consists of a dilatation of the ureter and kidney pelvis, usually more marked on the right side; this phenomenon is so common that it might well be said to be a normal concomitant of the pregnant state.
Probably the most widely recognized articles on the urinary tract of pregnancy are the papers by Hofbauer1 and by Duncan and Seng2 published in 1928. Hofbauer, working on ureters taken from women dying during pregnancy, showed by histologic methods that there was hypertrophy and hyperplasia of muscle and fibrous tissue of the ureter and the periureteral sheath, the greatest change taking place in the lower portion of the ureter, and from this he reasoned that there was produced an obstructive process which would account for the ureteral dilatation. Dugald Baird3 recently has confirmed this finding but
LEE HP, MENGERT WF. THE EFFECT OF PREGNANCY ON THE URINARY TRACT. JAMA. 1934;102(2):102-107. doi:10.1001/jama.1934.02750020014004