Association Between Gestational Weight Gain and Obstetric Anal Sphincter Injury
Bibliographic record
Abstract
OBJECTIVE: To investigate the association between gestational weight gain across all prepregnancy body mass index (BMI) categories and the risk of obstetric anal sphincter injury during vaginal birth. METHODS: Our retrospective population-based cohort study included individuals with singleton, term, vaginal births in the United States (2021-2023) and used data from the National Vital Statistics System's natality files. We examined the association between gestational weight gain (below, within, or above Institute of Medicine guidelines) and obstetric anal sphincter injury across BMI categories using logistic regression models. We assessed nonlinear associations between gestational weight gain and obstetric anal sphincter injury using restricted cubic spline regression and conducted a mediation analysis to examine the influence of fetal birth weight. RESULTS: Obstetric anal sphincter injury occurred in 1.2% of births, with rates of 1.3% among those who gained above the recommendations, 1.2% among those who gained within the recommendations, and 1.0% among those who gained below the recommendations. Gestational weight gain above and within guideline recommendations were associated with increased odds of obstetric anal sphincter injury among individuals with average-weight (adjusted odds ratio [aOR] 1.08; 95% CI, 1.05-1.10), overweight (aOR 1.13; 95% CI, 1.09-1.17), class I obesity (aOR 1.12; 95% CI, 1.06-1.18), and class II obesity (aOR 1.15; 95% CI, 1.06-1.26) BMIs. Gestational weight gain below and within recommendations showed a protective effect against obstetric anal sphincter injury only in individuals with average-weight BMIs (aOR 0.91; 95% CI, 0.88-0.93). Mediation analyses showed that gestational weight gain indirectly affected obstetric anal sphincter injury risk through birth weight across all BMI groups; direct effects were observed only in individuals with underweight, average-weight, and overweight BMIs. CONCLUSION: Gestational weight gain above the Institute of Medicine guideline was associated with increased risk of obstetric anal sphincter injury across all BMI categories except for underweight and class III obesity; weight gain below the guideline appeared to be protective only at average weight. These associations were largely mediated through birth weight.
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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 | 0.001 | 0.007 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".