The following are true of renal calculi in pregnancy, except:A. Pregnancy is an absolute contraindication to ureteroscopic stone removal
The incidence of urolithiasis in pregnancy is similar to that in non-pregnant women because a greater concentration of inhibitors of stone formation such as citrate, magnesium and glycosaminoglycans counter the effects of hypercalcaemia, hypercalciuria and urinary stasis. Pregnant women with symptoms suggestive of acute ureteric colic are best investigated initially by ultrasound particularly in the first trimester where radiation risks (teratogenesis, carcinogenesis and mutagenesis) are greatest. However, it may be difficult to differentiate acute ureteric obstruction from the physiological hydronephrosis that is often seen on the right side in pregnancy. Transvaginal ultrasound can be helpful to assess the distal ureter. MRI is advised as a second line investigation when results are equivocal and is able to define the level of urinary obstruction, visualise stones as a filling defect and can assess non-urological organ systems. Low-dose non-contrast CT KUB (foetal exposure 0.05 Gy versus 2.5 Gy) is increasing in popularity with a high sensitivity and specificity but still is last-line as exposure to ionising radiation can be associated with teratogenic risks and development of childhood malignancies. Conservative management is the preferred treatment option for pregnant women with ureteric stones as the majority will pass spontaneously. This may be the result of ureteral dilatation secondary to the effects of elevated levels of circulating progesterone. Where expectant management fails or intervention is indicated on the grounds of infection or in the presence of a solitary kidney, urinary diversion with a percutaneous nephrostomy or ureteric stent should be considered next. This usually leads to the rapid relief of symptoms but may necessitate frequent (up to six weekly) nephrostomy or stent changes because hypercalciuria leads to rapid encrustation. Ureteroscopy has been shown to be effective and safe in pregnancy with complication rates similar to those observed in non-pregnant women. On the other hand, pregnancy is considered an absolute contraindication to extracorporeal shockwave lithotripsy (ESWL) following studies on mice that demonstrated foetal damage and death in the later stages of pregnancy.