Q. Outline the main maternal renal tract changes during pregnancy.
A. Pregnancy results in generalised relaxation of smooth muscle (due to effects of progesterone), which in addition to mechanical factors such as dextro-rotation of the uterus contribute to the hydronephrosis of pregnancy commencing in weeks 6-10. Hydronephrosis is seen particularly on the right, probably due to the uterine dextro-rotation. By 28 weeks of gestation 90% of pregnant women will have hydronephrosis.
Pregnancy is associated with an increase in renal blood flow (up to 75%) and an approximate 50% increase in GFR. Creatinine clearance is There fore increased in pregnancy, and this is reflected in relatively reduced levels of serum creatinine and urea. Proteinuria increases up to 3 g/day and glycosuria is very common.
Q. A 24-year-old female is referred to you by the obstetricians. The patient is 21 weeks pregnant and has acute left loin to groin pain, a normal serum creatinine and no evidence of sepsis either clinically or biochemically. What imaging modalities are available to you diagnostically?
A. Ultrasound is the least invasive investigation, but is not particularly sensitive in the detection of ureteric calculi, and is obviously operator dependent. Hydronephrosis as mentioned above is not a specific marker for obstruction and stones; however a dilated ureter below the iliac vessels may be more suggestive of a stone/obstruction. The presence or absence of ureteric jets may also be helpful.
Intravenous urography (IVU) is feasible, but carries an inherent risk of radiation exposure. This modality is not commonly utilised; however the absolute risk of a (limited) IVU is low. The contrast media itself carries no specific risk to the pregnancy.
Regarding cross-sectional imaging, CT is avoided due to the relatively high radiation risk. MRI safety and pregnancy has not been fully elucidated, however an experienced radiologist may be able to detect the stone as a filling defect within the ureter, and this imaging modality is There fore sometimes used.
Q. The patient mentioned previously is found to have a left lower ureteric stone with moderate hydronephrosis on MRI and ultrasound. How should this patient be treated medically?
A. Close consultation with the obstetric team should be undertaken. Additionally, for those who are unfamiliar with prescribing in pregnancy the British National Formulary should be referred to. Simple analgesia such as paracetamol or co-dydramol may be used, but non-steroidal antiinflammatory drugs should be avoided (particularly in the third trimester) due to the risk of premature closure of the patent ductus arteriosus in the unborn. Maternal use of opiates such as pethidine and morphine are associated with respiratory depression in the newborn.
Q. What are the options for antibiotic usage in pregnant females with urinary tract infection?
A. Again, the British National Formulary should be referred to. Generally, penicillins or cephalosporins are safe in the non-allergic patient. Antibiotics used commonly in nonpregnant patients may have adverse effects. Trimethoprim’s mechanism of action is to interfere with bacterial dihydrofolate reductase and the production of folic acid. ttere is There fore the possibility of teratogenicity, particularly if used in the first trimester. Quinolones, such as ciprofloxacin, are contraindicated in pregnancy due to the risk of arthropathy in the foetus. Finally gentamicin has been found to lead to an increased risk of auditory or vestibular nerve damage in the second and third trimesters.