ABSTRACT

An appreciation of the anatomical, haemodynamic, renal tubular and endocrine changes that the healthy renal system undergoes during gestation is essential in interpreting the response of the diseased kidney during pregnancy. Dilatation of the ureters and renal pelvis occurs pro-

gressively during pregnancy.1,2 This predisposes to urinary stasis and increased risk of urinary tract infections (UTIs). Kidney size increases by 1-1.5 cm, with renal volumes increasing by 70% by the third trimester, probably due to intra-renal fluid and vascular expansion.3 These changes may mimic obstruction and imaging should be interpreted cautiously. The changes persist for around 12 weeks after delivery. In the first two trimesters, there is an increase in

renal plasma flow of 50-70%. This gestational hyperfiltration leads to an increase in glomerular filtration rate (GFR), which peaks at the end of the first trimester and remains elevated throughout.4,5 In a study of ten healthy females, mean creatinine levels were 73mmol/l in non-pregnant state, falling to 60, 54 and 64mmol/l in successive trimesters.5 Thus, levels of creatinine and urea within laboratory normal parameters may actually represent impaired renal function during pregnancy. Suggested upper limits of normal in pregnancy are 75mmol/l of creatinine and 4.5mmol/l of urea. Levels above this should prompt concern.6