† Hormonal factors that control the course of pregnancy as well as the pressure of the gravid uterus on the ureters cause physiological changes in the kidneys and ureters of at least 90% of pregnant women. Mechanical pressure occurs only at the pelvic brim, but the hormonal influences producing dilatation, atony, and reduced irritability of smooth muscle involve the entire upper urinary tract. Previous diagnosis of urinary disease or congenital anomalies is important in anticipating these changes. Pyelonephritis is still frequent, but its management in pregnant women is no longer different from that in the non-pregnant. Preexisting surgical renal disease must be carefully evaluated before pregnancy is permitted; disease discovered during pregnancy may or may not necessitate therapeutic abortion. The decision in either case depends on the nature and extent of the renal disease, the general health of the patient, and, in borderline cases, the risks that the parents are prepared to take in order to obtain a child.
Kittredge WE, Crawley JR. SURGICAL RENAL LESIONS ASSOCIATED WITH PREGNANCY. JAMA. 1956;162(15):1353-1356. doi:10.1001/jama.1956.02970320001001