More publications support the statement that maternal periodontitis may be a risk factor of preterm delivery and low birth-weight, than the number of those that suggest opposing evidence. The proving or rejecting of the questionable relationship may be carried out--among other methods--by analyzing the results of interventional studies. The aim of our study was to investigate whether or not it is possible to decrease the chance of preterm birth and low birth-weight in the case of healthy non-smoking women through the elimination of periodontal inflammation by providing professional oral hygiene treatment during pregnancy. After periodontal examination 80 pregnant women received professional oral hygiene treatment including plaque and calculus removal, root planing, motivation and instruction (treatment group); only the periodontal status was recorded in 79 cases (control group). The mean length of pregnancy and birth-weight in the treatment group were compared with similar data of the control group. Data were assessed using statistical methods. The mean weight of newborns was 3005.3 grams in the treatment group, while 2644.2 grams in the control group (p < 0.0001). The delivery occurred later in the treatment group (37.0 week), than among the control group (36.4 week), although the difference was not significant (p = 0.059). In the periodontal treated group, which had a statistically suitable number of members, the periodontal treatment might have contributed to a more optimal date of delivery and to achieving a larger birth-weight.