Reproductive and pregnancy outcomes following embryo transfer in women with previous cesarean section: A systematic review and meta‐analysis
Bibliographic record
Abstract
INTRODUCTION: Cesarean section affects subsequent spontaneous pregnancies because of implantation issues. However, its impact on post-embryo transfer pregnancies is still debated. This review aimed to evaluate the impact of a previous cesarean section on fertility and pregnancy outcomes of women undergoing fresh or frozen embryo transfer. MATERIAL AND METHODS: MEDLINE, Scopus, ClinicalTrials.gov, Scielo, EMBASE, Cochrane Library at the CENTRAL, and LILACS were searched from inception to February 2021. Studies were included if they evaluated reproductive or pregnancy outcomes after fresh or frozen embryo transfer in infertile women with a previous cesarean section relative to women with a previous vaginal delivery. Random-effect meta-analyses to calculate risk ratio (RR) or mean differences with 95% confidence intervals (CI) followed by subgroup analysis for fresh and frozen embryo transfer were performed. Risk of bias and quality assessment were conducted using Newcastle-Ottawa scale and GRADE criteria. The review was registered in the International Prospective Register of Systematic Reviews (CRD42021226297). RESULTS: Ten studies, with data provided for 13 696 participants, were eligible. For embryo transfers after cesarean section, compared with vaginal delivery, there was a significant reduction of the live birth rate (RR 0.88, 95% CI 0.79-0.99) and biochemical pregnancy rate (RR 0.89, 95% CI 0.82-0.96). No statistically significant differences were found for clinical pregnancy rate (RR 0.92, 95% CI 0.84-1.02), ectopic pregnancies (RR 1.00, 95% CI 0.68-1.46), pregnancy loss (RR 1.05, 95% CI 0.94-1.18), multiple pregnancies (RR 0.80, 95% CI 0.63-1.02), stillbirths (RR 0.86, 95% CI 0.27-2.69), birth defects (RR 1.71, 95% CI 0.49-5.96) or birthweight (mean difference 46.82, 95% CI -40.16 to 133.80). Subgroup analysis revealed an increased risk for preterm birth in post-cesarean section fresh embryo transfer pregnancies (RR 1.59, 95% CI 1.16-2.19). CONCLUSIONS: Low-grade evidence shows that post-embryo transfer pregnancies in infertile women who had a previous cesarean delivery result in reduced biochemical pregnancy and live birth rates relative to women with a previous vaginal delivery. An increased risk for preterm birth is notable in post-fresh embryo transfer pregnancies.
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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 | 0.008 | 0.024 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.014 | 0.024 |
| Bibliometrics | 0.004 | 0.005 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.003 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".