What Is Mean By Placenta Anterior Grade 1, Away From

What is mean by placenta anterior grade 1, away from OS.. is it safe.. i am 25 week pregnent.. details of scan: uterus: gravid position of fetus: floating Fetal Heart: pulsatile Fetal skull: Normal Fetal urinary bladder: Normal LMP: 14.08.2015 EDD: 20.05.2016 GA by LMP : 24 w 5 D BPD : 61.5mm 25 W 0 D HC: 225 mm 24 W 4 D AC: 202mm 24 W 6 D FL : 45.5 mm 25 W 1D EFBW:750 G GA by measurement: 24 W 6 D placenta : anterior grade 1, away from internal os, liquor volume normal. Fetal cardiac activity and movements normal. Internal os closed. Cervical length: 3.5 cm.