Postpartum Hemorrhage in Patients With a Low-Lying Placenta
Bibliographic record
Abstract
OBJECTIVE: We hypothesized that a second- or third-trimester diagnosis of low-lying placenta imparts underappreciated risk for postpartum hemorrhage (PPH) and placenta accreta spectrum (PAS). To quantify this risk and to assess whether it varies by the specific distance of the placenta from the cervical os and low-lying placenta resolution status, we conducted a systematic review and meta-analysis. DATA SOURCES: Systematic searches were conducted in PubMed, ClinicalTrials.gov , EMBASE, and Web of Science from database inception to April 30, 2024. METHODS OF STUDY SELECTION: A total of 3,700 results were screened for relevance with the PICO framework: population-singleton pregnancies; intervention-low-lying placenta; comparators-normal placentation; and outcomes-PPH and PAS. Studies published before 2000 were excluded to minimize bias from ultrasound sensitivity. TABULATION, INTEGRATION, AND RESULTS: Twenty-one studies (3,704 patients with low-lying placenta, 2,555 with normal placentation) were included. Data extraction and quality assessment with the Newcastle-Ottawa Scale were performed independently by three reviewers. At any gestational age, low-lying placenta imparted a significant PPH risk (risk ratio [RR] 2.10, 95% CI, 1.02-4.35, P =.05, I2 =0.0%) compared with non-low-lying placenta. The incidence of PPH was 16.0% (95% CI, 10.3-24.1%, I2 =93.3%) in low-lying placenta 1-20 mm compared with 5.8% (95% CI, 3.8-8.8%, I2 =79.9%) in non-low-lying placenta. When parsed by clinically meaningfully strata, a high incidence of PPH persisted with resolved low-lying placenta (resolved: 8%, 95% CI, 4.1-16.3%, I2 =85.0%; unresolved: 29.2%, 95% CI, 19.0-42.0%, I2 =70.5%; non-low-lying placenta: 5.8%, 95% CI, 3.8-8.8%, I2 =79.9%) with no difference in PPH risk at less than 2 cm from the os (low-lying placenta 1-10 mm: 16.6%, 95% CI, 9.2-28.3%, I2 =78.4%; low-lying placenta 11-20 mm: 17.5%, 95% CI, 8.8-31.7%, I2 =92.2%; RR 0.97, 95% CI, 0.67-1.41, P =.84, I2 =0.0%). An important finding is that PAS disorders affected 9.0% (95% CI, 4.7-16.8%, I2 =89.9%) of all low-lying placenta cases. CONCLUSION: Antepartum diagnosis of low-lying placenta is associated with a twofold increased risk of PPH compared with normal placentation. The pooled proportions of PPH were 16.6% in the 1-10 mm group and 17.5% in the 11-20 mm low-lying placenta group, with no significant difference. This meta-analysis is the first to quantify the risk of PPH associated with low-lying placenta, emphasizing the need for rigorous monitoring and delivery management of pregnancies with low-lying placenta to mitigate the burden of PPH on maternal morbidity. SYSTEMATIC REVIEW REGISTRATION: PROSPERO, CRD42024558043.
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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 | 0.009 | 0.037 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.004 | 0.006 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".