Yes it is possible for a woman to have a miscarriage without knowing about it.
Most times a woman who does have a miscarriage and they will know about it but sometimes a woman miscarries a baby and then never knows about it until they see a doctor.
However some signs of a miscarriage are vaginal bleeding and the vaginal bleeding when you have a miscarriage can sometimes be followed by cramping and pain in your lower abdomen.
If you suddenly experience vaginal bleeding and have cramping or pain in your lower abdomen and you're pregnant then you may have miscarried the baby and should see a doctor.
You can also go to the hospital if you do feel that you may have miscarried.
I miscarried my first baby and didn't know about it until I went to the doctor because I felt some cramping even though I never was bleeding.