<h3>Objectives</h3> To explore how US obstetrician gynecologists (Ob-Gyns) characterize periviable pregnancy-ending interventions as obstetric or abortion care, and to understand how those determinations are made. <h3>Methods</h3> From April to June 2021, we performed an explanatory sequential mixed methods study of US Ob-Gyns, recruited through overlapping online communities. We administered a cross-sectional survey requesting characterization of eight potentially ambiguous clinical scenarios, using chi-square tests to compare determinations by physician and institutional factors. We then conducted semi-structured interviews in a diverse nested sample, merging quantitative and qualitative data about decision making in a joint mixed methods analysis. <h3>Results</h3> We received 209 survey responses, with 101 (48.3%) current abortion providers and 42 (20.1%) never-providers, and completed 21 qualitative interviews. Characterization of pregnancy-ending interventions as induced abortion ranged from 21.1% for a 22-week labor induction in setting of chorioamnionitis, to 83.1% for a 24-week feticidal injection and labor induction in setting of fetal anencephaly. Interventions were less often characterized as abortion when performed for maternal indications, for instance only 42.6% of respondents felt a 22-week dilation and evacuation for chorioamnionitis was an abortion, compared to 82.1% for 24-week dilation and evacuation for anencephaly (p<0.001). Other significant associations with abortion determination included method type (procedural more likely than medication-only), abortion experience (ever-providers more likely than never-providers), and state and institutional abortion regulations ("I have to call it a medical inducement.…I'm not allowed to use the word abortion."). <h3>Conclusions</h3> Unclear definitions and administrative overreach lead to inconsistency and subjectivity in care for periviable pregnancy complications. With widespread abortion restrictions, characterization of interventions can affect access to necessary medical care.