Urinary tract infection in pregnant women: Old dogmas and current concepts regarding pathogenesis

Abstract

The dogma is that the higher risk of pyelonephritis in pregnant women is explained entirely by anatomic/obstructive changes. If so, gestational pyelonephritis should be caused by random, nonpathogenic bacteria. Instead, gestational pyelonephritis is associated with a narrow group of genetically related Escherichia coli and virulence factors, implicating a more complex pathophysiology. Current concepts in the pathogenesis of nongestational urinary tract infections propose receptor-mediated ascending infection. A pathogen with capacity to recognize various receptors may use receptors in the lower, rather than upper urinary tract, and ascend even the lumen of renal tubules. The immune system of a pregnant mother is modified to accommodate a semiallogeneic fetus. Gestational physiologic/immune adaptations may become additional risk factors, increasing sensitivity to urogenital infection. One could argue that it is not primarily the so-called "obstruction," but rather specific changes in the immune system and host receptors that act in concert with--or become exploited by--bacterial virulence that allow for infection in pregnancy to occur.

Urinary Tract Infections During Pregnancy

“…This was explained by the fact that genito-urinary anatomical and physiological changes induced by gestation predispose women with asymptomatic bacteriuria to develop symptomatic UTIs, leading to the impression that the number of UTIs was higher during this period of life (Nowicki, 2002). Nowadays, it is known that gestation itself is not the only responsible for the increased risk of UTIs.…”

“…There is some controversy concerning the role played by the physiological changes occuring during pregnancy which could be the main factor predisposing pregnant women to UTIs (Nowicki et al, 2011). Some authors claim that the biological complexity and molecular epidemiology of UTI suggest that mechanical obstruction can only partially explain the risk of developing gestational UTI (Nowicki, 2002). It is argued that if gestation alone predisposes to UTIs, urine stasis and obstruction should favour infection in the presence of avirulent random gram-negative and gram-positive species.…”

“…Pyelonephritis is the most severe form of UTI in pregnant women and may affect up to 2% of this population. Its occurrence is directly associated with the prevalence of asymptomatic bacteriuria among pregnant women (Gilstrap et al, 1981;Nowicki, 2002). This condition can occur with or without symptoms of cystitis.…”

“…In addition, asymptomatic bacteriuria does not present any clinical manifestation. However, patient history and risk factors can identify women at higher risk of UTI (Pastore et al, 1999;Nowicki, 2002;Fatima & Ishrat, 2006;Roos et al, 2006).…”

Septic Shock in Obstetrics and Gynecology

“…Acute pyelonephritis has an incidence of approximately 0.1-1% in pregnancy; most occurs at second trimester107. It is associated with multiple complications, including fetal growth restriction, preterm labour, cerebral palsy and septicemia, although the underlying mechanisms are poorly understood 108 . One mechanism could be the alteration in the profile of angiogenic and anti-angiogenic factors (increased expression of vascular endothelial growth factor [VEGF], decreased expression of PIGF and sVEGFR-2) observed in cases with acute pyelonephritis that resembles the one observed in sepsis 109 .…”