Streptococcus agalactiae, group B streptococci (GBS) are a constituent of normal vaginal bacterial microflora which often do not give any clinical symptoms. On the other hand, during pregnancy there are optimal conditions for GBS multiplication in the vagina, which may have very serious consequences for both the mother and her child. The women (n = 563) that participated in our study were in their 3rd trimester and they were divided into groups: normal pregnancy or high risk pregnancy. We also examined their newborns. GBS identification was done basing on traditional culture method and its modification recommended by the CDC. We showed a slightly improved (about 4%) effectiveness of GBS detection in pregnant women using the CDC method. In high risk pregnancy GBS colonization was 20% (among them 35% newborns were colonized) and in normal pregnancy it was found to be 17.2% (among them 26.7% newborns were colonized). Both in the high risk group and their newborns we confirmed a higher and statistically significant frequency of detection of GBS strains which had MLS(B) mechanism of antibiotic resistance. In newborns we confirmed two cases which were fatal. The results of our study show the need and necessity for implementing unified procedures recommended by the CDC in Poland.