Studies of nocturia in normal pregnancy.

Abstract

SummaryObservations were made on mean urine flow and the urinary excretion of total solute, sodium, potassium, urea and glucose in a 24 hour study and in an overnight study, each involving 100 pregnant and 100 non‐pregnant women. The findings reveal that the major cause of nocturnal frequency of micturition in the first and second trimesters is an increase in overnight urine flow, the increment being large in comparison with the change in 24 hour output. Overnight sodium excretion was also raised and was mainly responsible for the increase in urine flow. There was a reduction in the overnight excretion of urea relative to total solute excretion in the first and second trimesters and an absolute reduction in both overnight and 24 hour urea excretion in the third trimester; the significance of this observation is discussed. In a survey of 873 pregnant patients, the incidence of nocturia in the first, second and third trimesters was respectively 58, 57 and 66 per cent. Although the increment in mean overnight urine flow was smallest in the third trimester, measurements of urine voiding volumes suggest that in late pregnancy a decrease in functional bladder capacity is an additional cause of nocturia.