Ano po ibig sabhin ng distance from os no previa? at tsaka placenta grade3? thank you po

Hi. Posterior - yung placenta nakaposition sa likod ng matres Grade 3 - yung maturity ng placenta. Grade 0 : less than 28 weeks of gestation. Grade 1 : 31 weeks Grade 2 : 36 weeks Grade 3 : 38 weeks No previa - yung placenta hindi nakaharang sa cervix.