Hungarian Preconceptional Care includes the preconceptional screening of sexually transmitted infections/disorders (STD) and vaginal candidosis of potential mothers and pyospermia of potential fathers. The aim of this study was to evaluate the effect of this screening and treatment for the rate of preterm births. Clinical and subclinical vaginal candidiasis (asymptomatic candida colonisation), combination of STD and vaginal candidiasis, STD without vaginal candidiasis, finally women without STD and vaginal candidiasis as references were evaluated in 4,672 pregnant women. The association of STD in pregnant women with higher risk of preterm birth was confirmed. However, an association was also found between clinically diagnosed vaginal candidiasis, asymptomatic candida colonisation, and a higher risk for preterm births. This risk was reduced with clotrimazole treatment. However, pregnant women without recognized STD and/or vaginal candidiasis had a higher risk for preterm birth than pregnant women with STD or vaginal candidiasis after appropriate treatment. Thus the conclusion of the study is that the preconceptional screening of STD and vaginal candidiasis followed by appropriate treatment is important to prevent a certain part of preterm birth but it is necessary to improve the efficacy of the previously used methods for this screening.