Preterm birth continues to be a major challenge in obstetrics. One of the most important avoidable causes of prematurity is ascending genital infection. Regular screening for signs of such a disturbance using vaginal pH-measurements makes possible the detection of an "early marker" to prevent prematurity in an effective and inexpensive way. Abnormal vaginal flora (AVF), bacterial vaginosis & aerobic vaginitis (AV) are associated with preterm birth. Abnormal vaginal flora in the first trimester may be a risk factor for shortening cervix length at second and third trimester and may predict preterm delivery.