A systematic review of transvaginal ultrasound assessment of cesarean scar characteristics and prediction of adverse obstetric outcomes
Bibliographic record
Abstract
OBJECTIVE: This study aimed to investigate the association between preconception and antenatal ultrasound characteristics of cesarean delivery scars and adverse obstetrical outcomes in subsequent pregnancies. DATA SOURCES: Literature searches were performed in MEDLINE, Embase, and Cochrane databases from inception to January 31, 2024. STUDY ELIGIBILITY CRITERIA: Eligible studies included studies that evaluated cesarean delivery scar and niche characteristics using transvaginal ultrasound during preconception and/or antenatally and described subsequent adverse obstetrical outcomes (placenta accreta spectrum, preterm birth, uterine dehiscence/rupture, and unsuccessful vaginal birth after cesarean delivery). METHODS: A systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines (International Prospective Register of Systematic Reviews registration number: CRD 42019121523). Of note, 2 reviewers independently screened records and assessed eligible articles. The quality of publication was assessed using the Cochrane Collaboration tool and Newcastle-Ottawa Scale. The data were summarized using descriptive statistics. RESULTS: In 19 included studies, the definition of niche, large niche, and cesarean delivery scar assessment timing varied widely. Scar visibility was reported to be between 78% and 100% in the first trimester of pregnancy and between 68% and 91% in the second trimester of pregnancy. The prevalence rates of niche detection were 65% to 97% before conception and 52% to 58% during pregnancy. Uterine dehiscence/rupture was the most common adverse outcome reported (13 studies) and was associated with a large niche, a higher niche depth-to-residual myometrial thickness ratio (≥0.785), a thin residual myometrial thickness, and a higher average decrease in residual myometrial thickness between the first and second trimesters of pregnancy. Owing to methodological study heterogeneity and insufficient description of definitions, optimal cutoffs could not be defined. Of note, 3 studies evaluated the screening for placenta accreta spectrum using first-trimester cesarean delivery scar characteristics. An exposed cesarean delivery scar above the cervicoisthmic canal with placental implantation over the scar or within the niche had high sensitivity (75.0%-100.0%) and negative predictive value (99.6%-100.0%) for placenta accreta spectrum. Of note, 1 study found that a low scar after full dilatation cesarean delivery (a scar within the cervix or <5.0 mm above the internal cervical os) was associated with an increased risk of shortening cervical length and/or spontaneous preterm birth (adjusted odds ratio, 12.7 [95% confidence interval, 4.5-36.0]; P≤.0001). CONCLUSION: This systematic review found that cesarean delivery scar characteristics are associated with adverse obstetrical outcomes, including uterine rupture/dehiscence, placenta accreta spectrum, and spontaneous preterm birth. Multicenter prospective studies using standardized cesarean delivery scar assessment are needed to establish predictive data for optimal management and pregnancy counseling. El resumen está disponible en Español al final del artículo.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.012 | 0.068 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.012 | 0.013 |
| Bibliometrics | 0.013 | 0.013 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.003 | 0.003 |
| Open science | 0.002 | 0.002 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".