Usually the placenta is on the top of the uterine cavity
.Ve,.Ary rarely this things can happen now it is near the mouth of the uterus
A,s the baby grow it may migrate up wards ,till that time there are chances of bleeding if you strain too much .Take scan next month ,till it comes to normal position avoid heavy work , long journey , constipation
,coitus ,two wheeler riding Know your blood group
in case of emergency.