as to what causes stammering, there is no single cause for it.
its more likely to be of genetic nature thn of it being part of human behaviour or jst a habitual mistake...sometimes in some cases it was because of functional prob related to diaphragm ,,once a surgery was done, they were fine...but as to how it actually causes its quite unknown n a single cause was difficult to note !!

But, it may become worse in your child case,,in accordance to how the communication happens in your family before your child. if mother has problem and being the only caregiver, if she happens to teach the child in the same way,,,child will LEARN just the same way,,,even if he was ready to speak in better way or was able to speak clearly without repetition.

so the possblty from your side is reduced if the caregiver of the child teaches the child clear speech without repetition thru out the entire childhood years,,which is until 5years,,,...

but, never think that if your child has got this prob,,there is pssblity that he wil outgrow it in longer run,,esp after all trials from your side...

Though the recovery rate of stammering is like 60-75%,,its difficult for one to predict whther or not the child has taken the stammerng as problem of speech or the genetic makeup has affected it or there are ne other pyschological facts involved like extreme anxty, lack of confidence of what he is speaking, fear of parent that if he speaks somethng in someway, parent might get angry and in that he happens to speak it that way,,etc.
its difficult to predict so early at age below 5-8years,,
about the physiological factrs if we talking about,,it depends on how far that genetic link that was prominent in that particular environment(body) and how far it will actually suceed in making the child stammer in relatn to his upbringing and other genetic links from the other parent who doesnt have stammr prob,,has played the role..

its like nature vz nuture/care. if the person is broughtup in an environment, where his caregiver taught him speech without ne stammerng thn the chances are quite reduced(even though parent himsef used to stammer but he made sure that while teaching his child he controlled it somehow or reduce the repetitn of words and child happend to picked up the right words only),,,because its not all the words that they happen to speak like that...thn its practice how he is able to himself outgrow it....

boys are more vulnerable,,the reason is quite unknown,,but the studies have shown that out of 50 boys and girls,,the recovery rate of girls were better and quite clear thn those of boys----considering the environment they were broughtup in, the direct genetic link of person/father or mother who was stammerng or ne blood relative had or is still having stammerng prob.....

recently study also shows some connectivty to anatomy of brain,,but its just a prelimnry posblty and not the study in progress.

most stammrng begins at childhood, mstly from2-5years,,and this is just the right time when the children are devlopng thr speech, makng thr sounds clear, and are sharpng thr language skills,,,so,,during that time,,make sure if you have neone in family is stamrrng stays away from child or speaks in a way that child doesnt notice that natural habit,,or if you have a hstry of stammrng,,,thn make your child intrduce to clear speech without repeatitn, clear language and whenver he seems to stammr (which he himself might not be aware),,correct him to speak it only once...keep doing that and try your best from your side,,,,rest well,,its upto him thn and yes, consult a good speech therapist.none can help best thn he can...

so thats all i know about stammerng upto my reach ! this is not my area of study so i cant help you more thn this !!!!
you can view the below site, see if helps you find some other details...
also there are very nice speech development centers where these kind of cases are succsfully solved with tutorials and regular practice for all ages,,,in india too there are many,,just look around,may b there could be one right in your city !

http(:)//www(.)stammeringcurecentre(.)com/introduction(.)html

good luck to you ! preti replied. dear Hetal,
thanks a lot for ur message.thank u so much for taking ur precious time to write to me. ur message was very helpful & informational.i'll definately follow ur advice strictly.i'll always be cautious when i speak with my child.i'll make sure that i dont stammer in front of the child.ur message gave me hopes that atleast i have some chances to prevent my child from stammering.
thanks a lot once again
God bless u & ur family