In Finland, 50 000 to 60 000 children are born annually. The birth of every new family member is a unique and invaluable event for the family. During the pregnancy, a mother undergoes several physiological and psychological changes while the transition to parenthood emerges. High-quality maternal care is offered to every Finnish family who is expecting a child and maternal morbidity and mortality rates are among the lowest in the world. Giving birth and being born in Finland is therefore safe. Gestational diabetes mellitus (GDM) and perinatal depression are globally common complications during pregnancy. Currently, in Finland, almost one out of five women has an abnormal oral glucose tolerance test (OGTT) result during pregnancy. After pregnancy, women with GDM and children born to mothers with GDM are in increased risk for metabolic disturbances and type 2 diabetes (T2D). Perinatal depression affects at least one out of ten women in Finland. Maternal depression causes psychological suffering and may predispose the offspring for health problems. GDM and perinatal depression increase the risk of unfavourable pregnancy outcomes and, if neglected, may negatively impact the future health of the mother and her child. The risks can be reduced with appropriate treatment, and both GDM and perinatal depression are currently suggested to be screened in Finnish maternity care. GDM and perinatal depression may intertwine with shared risk factors such as obesity, a sedentary lifestyle, and low socioeconomic status (SES). A healthy diet and sufficient physical activity (PA) have a beneficial impact on glucose metabolism, and healthy lifestyle choices may postpone or even prevent GDM and later T2D. PA has also been shown to associate positively with psychological well-being, though interactions are complicated. Health-related Quality of Life (HRQoL) is a multidimensional concept which includes the individual's perception of physical and mental health status, including functional, social, and environmental aspects. There is currently little knowledge of the determinants and trajectories of HRQoL in the Finnish population during pregnancy and the peripartal period. Also, there is little evidence on the effects of interventions provided during the peripartal period on maternal HRQoL. The aims of study I and study II were to examine determinants of HRQoL among Finnish pregnant women from early pregnancy (Study I) until the first year of motherhood (study II). In study III, the aim was to estimate the effect of lifestyle counselling on HRQoL among intervention and control groups of the Finnish Gestational Diabetes Prevention Trial (RADIEL), a lifestyle intervention trial for women at high risk for GDM. Study IV aimed to describe the amount of PA and correlations between PA and HRQoL after the delivery among a sample of women participating in the RADIEL trial four to six years earlier. To study the peripartal HRQoL in an unselected pregnant population (studies I and II), 325 women were recruited from the first trimester ultrasound appointment offered to all Finnish pregnant women during the pregnancy from gestational week (gw) 10+0 to 13+6. HRQoL and depressive symptoms were assessed with 15D and Edinburgh Postnatal Depression Scale (EPDS) questionnaires at 5 timepoints from early pregnancy until 12 months postpartum. In study I, the women were divided into three groups according to their perceived financial satisfaction (unsatisfied, somewhat satisfied, and satisfied) and in study II the women were divided into three groups according to their Body Mass Index (BMI