I was given my baby fetus

I had a miscarriage on june 9 and june 10 i had to get a d&c; they gave my my baby in a little jar the doctor couldn't explain what cause the miscarriage the baby was smaller than it was supposed to be i was 10 weeks he just had his lil eyes forming and spine no hands no legs the doctor said many things can cause it but i would love a solid explanation why wasnt my baby growing like he was supposed to i camt get over it and in 3 months im trying again i hope this baby come out healthy i just need a explanation help me what do you think its was i had blood test and i was fine healthy i have a pre pregnancy checkup next month just help please