Bottle tooth decay is a common problem in dental medicine. Studies point to the relationship between mother's knowledge and motivation to maintain oral hygiene and child`s oral health. The reason behind it is that mothers are usually the ones spending most of the time with the child during first years of life. The purpose of this study is to examine the level of pregnant women's knowledge of the importance of primary teeth, caries and its causes, best time to begin tooth brushing and best time for first dental visit. In infant oral health lectures within the pregnancy class, 49 pregnant women were examined. The average age was 31, most of them were educated and employed. Before and after the lecture pregnant women got the same questionnaire and the results of the second questionnaire provides information on the importance of the lecture given within the course of pregnancy. Research results show that pregnant women consider primary teeth very important to child´s development and general health. Most of them were aware that cleaning child´s mouth starts even before the first primary tooth appearance and that primary teeth should be restored if necessary. Significant number of respondents knew the exact time of first tooth appearance. Knowledge of the recommended time for first dental visit and the caries risk factors was shown poor. The conclusion is that most pregnant women are unaware that breastfeeding, bottlefeeding, using bedtime bottle and frequent feeding cause caries. Lecture on child´s oral hygiene proved to be extremely useful because for most pregnant women that was the first time they got that information