We present findings from a study that investigates how people engage in self-tracking as they experience a major life transition. Using pregnancy as a case study, we inquired 41 pregnant women into how their pregnancies shaped their use and engagement with self-tracking tools as they transitioned into their pregnancies. Our study highlights some of the challenges that transitions place on self-tracking, including misalignments between one's past data and current realities, and ways of realising goals. We discuss these challenges and suggest ways in which self-tracking could better account for realities which consider changing lives, bodies and identities. CCS CONCEPTS• Human-centered computing; • Interaction design; • Interaction design process and methods; • User interface design;