How do you know if have had a miscarriage on the 10th day after conception?

It is extremely unlikely to have a miscarriage within 10 days of conception. Most couples do not even know they are pregnant in the first 10 days of conception, as this is well before a missed period. Additionally, even if you did somehow know that you were pregnant on the 10th day after conception, it is very unlikely for a pregnancy to spontaneously end so early in the conception phase.