Pregnancy is a special physiological condition in a woman’s life. It usually involves a substantial change in health behaviour and lifestyle. The aim of rational nutrition among pregnant women is to prevent complications during pregnancy and ensure normal development of the foetus. Practical realisation of the principles of rational nutrition involves the application of a balanced diet. It limits both shortages and excessive amount of nutrients in the body. The aim of the paper was to evaluate health behaviour of pregnant women with secondary and higher education and the level of knowledge about healthy lifestyle and its impact on child development. The study included 43 pregnant women aged 20–40 years from Gdańsk birth schools of higher and secondary education. The study based on questionnaire provided information about the current state of knowledge about nutrition while pregnant and assessed the health behaviour of women: nutrition, substance abuse and physical activity. A pilot study reported that 84% of pregnant women were interested in proper nutrition while pregnant. An increased amount of food consumed per day (69%) and portions of fruit and vegetables (98%) was noticed. Also, it was noted that 58.1% of the respondents did not increase the consumption of sweets. Good appetite was observed only in the case of 53% of studied women, 47% presented loss of appetite; 19% of the respondents occasionally consumed alcohol, 30% drank coffee once per day and 9% several times a day. There was no woman smoking tobacco. Among the respondents, physically active ones included 51.2% and 39.5% did physical activity occasionally. The studied group of pregnant women with secondary and higher education changed their eating habits during pregnancy. Preliminary analysis of the results indicates the validity of conducting nutrition education in antenatal classes, which raises the nutritional knowledge and has a positive effect on health behaviour modification in a specific group of pregnant women.