why do some women have menses cycle change?

for eg, a women is having her regular menses every mth and suddenly she had a mth of menses and nxt mth the menses does not come as regular as before.

It happens. Stress, diet change, excercise change, pregnancy, miscarriage, birth control pills, all these things can effect our cycles.

It's the joy of being female.

other than those u have stated is there anythin else? i don think all those things happen to my gf.

Menstruation cycle can be affected of your heredity.