The aim of the study was to prediction of sub-clinical infection as a cause of preterm- prelabour rupture of membranes (PPROM) and preterm labour. Maternal and cord blood for C-reactive protein (CRP) estimation as screening test and urine, high vaginal swab and placental swabs for culture and sensitivity as a confirmative test for sub-clinical infection. Thirty pregnant of (24-37) weeks gestation with PPROM as study group and 30 pregnant of same gestation age with intact fetal membranes but in labour. All submitted to CRP test, high vaginal swab, placental swab for C/S and cord blood for CRP. CRP positive in study group 18 cases (60%) and control group 8 cases (36.6%) for urine C/S in study group was 11 cases (36.6%) and in control group 2 cases (6.6%) for high the vaginal swab positive in study group 8 cases (27.3%) and in control group 3 cases (10%), CRP test, urine for C/S and high the vag. swab for C/S all were statistically significant. Cord blood CRP and placental swab for C/S were statistically not significant CRP test sensitivity was 78% and specificity was 62.5% So CRP test can used as screening test for infection.