Hi Welcome to Healthcare Magic ...
Yeah placenta does move up to some extent with progressing weeks of pregnancy
So repeat ultrasound
by 32 weeks would be more informative in diagnosing placenta previa
. In case u have placenta previs , u need to take few precautions -
1) depending on the degree of placenta previa u may need to get a cesarian section done to deliver your baby.
2)u have more chances of bleeding near term , so need to be more cautious and have adequate bed rest
and avoit more jolts and heavy labour.
3) Get in touch with an obstretecian and plan for your delivery , better before onset of labour.
Hope i was helpful.