Advice to take test is to improve the placental  sufficiency .                                                                1. I  think you might have been explained by your gynacologist often placenta moves upwards later if not you should be careful till delivery .                                                                    2. If you do strenuous work .& even having sex  results in bleeding  which can cause abortion , placental insufficiency , fetal death . 3 .I if heavy bleeding occurs due to placental seperation there is danger to the mother also .

No effect on fetus....don't need bed rest Just avoid heavy work

Hi. At 16 weeks placenta will be near the os if it is low lying . Gradually it will be away from os . So nothing to worry . Bed rest is not required . Avoid strenous activities .