How do you know everything came out during a miscarriage?

Well I had a natural miscarriage ( had a gestational sac but no baby) but usually your soppose to check up with your doctor and they willl either do a ultrasound or test your hcg levels or both. However you can take a pregnancy test to see if you test positve because its basically the same thing the doctor does or you can tell by your bleeding stopping. I'm no doctor I'm just going by experience. Like I said I had a miscarriage natural with no check up because I'm sure everything is out and my first period was awful lots of pain and blood clots. Still I recommend to see a doctor.