Previous cesarean characteristics among women with and without cesarean scar pregnancy: an exploratory hospital-based case–control study in Vietnam

Cesarean scar pregnancy (CSP) is a high-risk ectopic pregnancy after cesarean delivery. Whether the recorded timing of a previous cesarean delivery in relation to labor is associated with CSP remains uncertain. We conducted an unmatched exploratory hospital-based case–control study in Ho Chi Minh City, Vietnam (November 2023 to April 2024). Cases had a first-trimester ultrasound diagnosis of CSP. Controls were first-trimester hospital antenatal attendees with a previous cesarean delivery and an intrauterine pregnancy not classified as CSP, enrolled against accruing cases to a fixed 1:3 quota rather than sampled from an enumerated frame. The primary exposure was the recorded prelabor classification of the most recent cesarean delivery, as retained in the study dataset. Analyses comprised crude comparisons, a parsimonious Firth penalized logistic regression, two restricted analyses, and sensitivity analyses. The sample comprised 59 CSP cases and 177 controls. The recorded prelabor classification was more frequent among cases (37/59, 62.7%) than controls (55/177, 31.1%; crude odds ratio [OR] 3.73 95% confidence interval [CI] 2.01–6.91). Adjusted for maternal age and number of previous cesarean deliveries, the Firth OR was 2.62 (95% CI 1.33–5.19; p = 0.006). Restricted to one prior birth: 10/12 versus 31/129 (OR 15.81, 95% CI 3.29–76.05); restricted to exactly one previous cesarean delivery: 14/21 versus 39/145 (OR 5.44, 95% CI 2.04–14.47). These strata are nested, not independent replications. Two descriptive observations were directly available from the retained dataset: 59 of 177 controls (33.3%) were in the closest recorded sac-to-scar distance category (< 20 mm) without meeting ultrasound criteria for CSP, and 18 of 59 cases (30.5%) were asymptomatic at presentation. In this included hospital-based sample, the recorded prelabor classification was associated with CSP after penalized adjustment and in restricted analyses. These findings are exploratory and hypothesis-generating and cannot establish an independent causal effect: the study base could not be established, inclusion in the final analytical dataset required ascertainable information on the previous-cesarean timing and indication, comparable pre-enrolment control screening and exclusion data were unavailable, exposure provenance is not reconstructible, and central image re-review was not possible. The two descriptive findings support careful first-trimester pregnancy localization after cesarean delivery. Screening effectiveness, diagnostic accuracy and treatment outcomes were not evaluated.