I am 8 weeks pregnant but The baby's heartbeat has not come yet, what could be the reason for this....the doctor is saying that everything is fine, he has called after 20 days

A. The fetal heart should be there by six weeks of pregnancy and sometimes theyrecould be wrong dates where because you don’t know when the ovulation has happened, you might be calculating the dates differently. Its better to have to wait for another one week to 10 days and repeat the scan and then take a call