Prevention of prematurity and of low birth weight is – because of the associated increased risk of mortality and morbidity – one of the most urgent tasks of perinatal medicine. Whereas the rate of prematures all over the world does not vary very much (5–10 %), the rate of infants born with low birth weight lies between 3.6% and 10% in the industrial countries and between 9.8% and 43% in the developing countries, where the main cause of low birth weight is intrauterine malnutrition. As there are different causes for prematurity and low birth weight, but also because various countries have different resources and have therefore to set their priorities differently, there is no global solution. The situation in each country must be considered individually. However, as far as basic means are available for the majority – such as basic health care, monitoring the nutritional state of the mothers and acting to prevent infectious diseases (malaria in particular can cause prematurity) – determined prevention of prematurity should take the form of screening and the treatment of disturbances of the vaginal milieu or genital infections. This policy can be recommended because one of the most important avoidable causes of prematurity is ascending genital infection (mostly combined with bacterial vaginosis), which very frequently starts with a disturbance of the vaginal milieu and then often takes its course asymptomatically. Regular screening for signs of such a disturbance using vaginal pH-measurements (and if necessary further diagnostics and therapy) makes possible the detection of an “early marker” to prevent prematurity in an effective and inexpensive way. Our prematurity-prevention-program, which has been successful for many years, is based on an anamnestic assessment of prematurity risk, the early detection of warning signs (including regular measurement of the vaginal pH) and, if necessary, the appropriate therapeutic measures. In cases of disturbance of the vaginal milieu, the latter consists of a therapy with lactobacillus preparations or in a combination of lactobacillus preparation with an acidifying therapy which may lead to earlier normalization of the vaginal milieu. In cases of bacterial vaginosis local therapy, for example with metronidazol or clindamycin, is undertaken, and in other infections specific treatment. It is encouraging to note that particularly the rate of the very small prematures is reduced when pregnant patients take part in our self-care- program, measuring their own vaginal pH-value twice a week, and also searching for any other warning signs. In this way in our collective the rate of very small low birth weight infants could be reduced from 7.8% in the immediate previous pregnancy to 1.3 %. In a prospective study performed in Erfurt the rate of very early premature births (< 32 + 0 gw) amounted to only 0.3% in contrast to 3.3% in a control group who had not taken part in the self-care activity. According to a differentiated classification of the control group the success of the self-care activity was even clearer: In patients who did not take part because their doctors did not support the self-care activity, the rate of very early premature births amounted to 4.1 %. In patients who did not take part in the self-care activity, but who were in the care of doctors who were interested and had taken part in the prevention-program, the rate was 2.2 %; in the group with active participation in the self-care activity it was only 0.3 %. To date measurement of the vaginal pH-value was performed intravaginally using either indicator strips or pH-measuring test gloves. A short time ago we developed a panty liner coated with an indicator strip, which enables reading of the pH-value by just checking the indicator on the panty liner. First results with this panty liner are very promising.