10 - Pregnancy and the renal tract

Summary

Many women experience lower urinary tract symptoms during pregnancy, and childbirth is commonly cited as the cause for subsequent urinary, colorectal and genital dysfunction. Pregnancy also predisposes to concurrent pathology such as urinary tract infections and hydronephrosis.

Filling symptoms

Between 45% and 90% of pregnant women experience frequency of micturition. This may develop in the first trimester but becomes most noticeable towards the end of pregnancy. It is due in part to the increased production of urine secondary to increased renal plasma flow but in the third trimester the enlarging uterus or presenting part may also cause vesical compression.

Nocturia is often noted for the first time in pregnancy and it is rarely pathological. If defined as at least two nocturnal voids, it affects between 22% and 65% of pregnant women. It may be due to increased production of urine and mobilisation of dependent oedema when the legs are elevated during sleep.

Urgency is also common, with between 60% and 70% of pregnant women describing the symptom. It has been proposed that high progesterone levels may predispose to detrusor overactivity during pregnancy. However, there is a poor correlation between symptoms and urodynamic findings: detrusor overactivity is confirmed in only one in four women complaining of urge incontinence during pregnancy. Anticholinergic medication is best avoided in pregnancy because of potential adverse effects and toxicity. High doses of oxybutynin have been toxic to the developing fetus in animal studies and manufacturers of tolterodine advise avoidance in pregnancy as no information is available to confirm its safety. Management, therefore, is limited to physiotherapy, caffeine restriction and bladder training.