The reason why pregnant women urinate frequently is this.

The bladder is closely related to the rectum as well as to the organs of the genital tract and all organs are supplied by nerves from the sacral plexus. In pregnancy also, because of the developing fetus, they are all competing for decreasing space in the pelvis. As one organ enlarges another is compressed, and it is therefore not unusual for disturbances of micturition to occur in pregnancy and labour as well as during the postnatal period.

In pregnancy

In the first 12 weeks of pregnancy, while the enlarging uterus is still a pelvic organ, the bladder requires to be emptied at more frequent intervals because there is less room for it to expand. This type of increased frequency is said to be Physiological. During the last 4 weeks of pregnancy, when the fetal head lies in the pelvis, there is a recurrence of increased frequency for the same reason. In the middle weeks of pregnancy, increased frequency arising in association with dysuria is due to urinary infection. This commonly arises between the 16th and 24th weeks of pregnancy, and is a difficult condition to cure at this time. It may recur thought-out pregnancy and the puerperuim. About 2% of pregnant women are affected.

Acute Retention

This is a rare complication of pregnancy but sometimes occurs at about the 12th week of gestation if the uterus is retroverted. The uterus cannot rise out of the pelvis beyond the hallow of the sacrum if the bladder is full and the uterus therefore becomes impacted. This is a vicious circle: the uterus cannot rise out of the pelvis until the bladder is emptied, but the bladder cannot be spontaneously emptied because it is nipped between the symphysis pubis and the enlarged uterus. The treatment lies in passing a urinary catheter and slowly draining the bladder, after which there are rarely any further complications because the uterus can then stand erect and rise out of the pelvic cavity.

Stress incontinence 

Urine is sometimes passed involuntarily towards the end of pregnancy if the fetal head is deeply engaged in the pelvis. Small amounts of urine may be passed if the patient coughs, sneezes or laughs. Incontinence of urine should not be confused with early rupture of membranes. In order to make a differential diagnosis, the pH should be determined. Urine has a pH of 5.3-6.0, while amniotic fluid is alkaline.

In labour

Increased Frequency.

This occurs most commonly in association with the occipitoposterior position of the fetal head. The occiput of the deflexed head applies increased pressure on the nerves of the sacral plexus and with the consequential increased stimulus of sensory receptors in the bladder wall, the women has a more frequent desire to micturate. It is sometimes an almost continual desire even though Intravesical pressure is not increased. Only very small amounts of urine are passed at each attempt.

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