Bladder Control - Factors that Influence Bladder Size in Children

Bladder Size in Children

The size of the child influences the size of the bladder. More precisely, the volume of the pelvis influences the size.

The bladder volume of a newborn infant is only about 50 ml. By one year the growth of the child is such that the volume is 130 ml, and by two years the volume is 175 ml. Thereafter, the bladder increases slowly by about 30 ml (one oz) per year of age. In a six year-old child in grade one the volume should be 275 ml. At ten years the volume should be 335 ml.

Bowel health has a major influence on bladder size. The bladder is designed to push a liquid out of a hole. The muscles of the bladder are not suited to push solid poop out of the way. The poop in the rectum therefore competes for space at the narrow bottom of the pelvis. The optimal bowel pattern to achieve an average size bladder is to poop every day in the morning after breakfast and a second time later in the day. The poop must be soft enough for the bladder to push out of the way.

Personality modifies how a child responds to the early signals of a full bladder. There is a spectrum of attentiveness to the early bladder signals. Some children are very attentive and never hold their pee past full. These children void more frequently at smaller volumes. Some children are not very attentive and tend to hold their pee past full and then race to pee and they might be damp or wet before they reach the bathroom. The "Attentive Voiders" present with smaller bladder volumes for size and bowel health. Perhaps there is a "muscle memory" situation that develops to account for this.

Pelvic size, bowel health, and personality are the major modifiers of bladder volume.

There are a number of other modifiers that might intermittently play a role.

The rate of bladder filling is a factor. A faster filling rate triggers the need to pee at a smaller volume. A faster filling rate happens when a child has a larger than usual amount of water or juice to drink and the kidneys are quickly making pee to excrete the excess fluid. think of how often some children need to pee after drinking a big pop at the movie theatre. 

Changes in the emotional state can modify bladder volume. Children who are excited (positive or negative) or anxious pee more often.

Cold temperature plays a role. The bladder empties at a smaller volume when the ambient temperature is low.

The sound of rushing water (taps, waterfalls, river noise) can trigger the need to pee.

Drinking water fast can trigger the need to pee. 

Bladder Control - Children who are “Rule Followers.”

A six year-old boy was referred for bedwetting. The boy wets every night.  He pees 7 times a day including at the prescribed time during morning kindergarten. Mom described him as a “rule follower” and scored him 9 out of 10 on the “perfectionist” scale.

This boy is an Attentive Voider. He does not hold his pee past full. His mother does not see holding postures, he does not need reminders to pee, he is not in a rush to pee, and he is always dry without even minor daytime dampness.

This boy is also a "rule follower." Many elementary school teachers request that a child only pee at break times. This message from a respected adult authority figure can have a strong impact on the behaviour of a young child. Likely this boy will only pee at scheduled breaks at school and he might be reluctant to ask to leave class to pee.

The combination of an Attentive Voider and a Rule Follower means that he will not drink much at school. Attentive voiders do not like the feeling of an overfull bladder or they are not prepared to risk daytime wetting, not even a few drips. Rule Followers restrict their trips to the bathroom to the scheduled breaks.  These children learn to self limit their fluid intake to allow them to stay attentive to the signals and to follow the rules.

Some of these children learn to pre-emptively pee at every break to make sure they are never overfull. These children also learn to pee before they get on the school bus.

Since they do not drink much at school, these children end up with very solid stool. The stool presses on the bladder and compromises bladder capacity. Children with a smaller bladder need to pee more often after they drink and since this might oblige them to leave class to pee, they learn to drink even less.

The body has healthy rules that should be followed and that are much more important than arbitrary rules about bathroom breaks at school. Paying attention to a bladder signal is an important rule. Holding the pee to wait for a break is not a healthy practice. Parents should empower their children to routinely leave class to pee and never to hold their pee to wait for a scheduled break.