Fizikai inaktivitás terhesség alatt: összefüggései a társadalmi-demográfiai háttérrel és a mentális egészséggel Exercise during pregnancy is known to have positive effects on both maternal and foetal health. Despite international recommendations advocating regular exercise for healthy pregnant women, survey data indicate that physical activity decreases during pregnancy, particularly in the third trimester. This study aims to assess the physical activity levels of pregnant women in Hungary in a representative sample and to explore the association between physical inactivity, socio-demographic characteristics, and mental health. Utilizing data from the Cohort ?18 Hungarian Birth Cohort Study, our analysis encompasses 6,121 pregnant women. Maternal physical activity was assessed in the third trimester, both for the time of the interview and retrospectively for the pre-pregnancy period. Mental health was evaluated through the CES-D-8 and GAD-2 questionnaires. The inactivity rate (defined as less than 1 hour per week) in the third trimester was 70% for walking, 92% for cycling, and 90% for sports. Inactivity increased across all forms of physical activity during pregnancy. The socio-demographic determinants influencing physical activity during pregnancy varied for different activities. The examined socio-demographic variables explained 3.5-4.7% of the variance in walking, 3.3-7.8% in cycling, and 714% in doing sport during pregnancy. Mental health was only significantly associated with sport activity. These findings underscore the importance of raising awareness about physical activity in antenatal care, particularly targeting at-risk populations.  Kulcsszavak: pregnancy, physical activity, socio-demographic background, mental health