P-694 Is Body Mass index (BMI)<18.5 kg/m² the Best Cut-Off for IVF Success? Reevaluating the lower BMI Threshold
Bibliographic record
Abstract
Abstract Study question What is the optimal BMI threshold for predicting lower live birth rates in IVF—18.5 kg/m² or a different cutoff? Summary answer Low-normal BMI(18.5-20.0kg/m²) is associated with significantly lower live births when compared to a BMI(20.0–25.0 kg/m²), suggesting how to define BMI thresholds for reproductive health. What is known already A U-shaped relationship between BMI and IVF outcomes has been described, with the negative effects of obesity extensively studied, while the impact of being underweight remains less explored. Furthermore, variability in IVF outcomes within the “normal” BMI range has not been well defined. The WHO established BMI categories based on epidemiological data linking BMI to general health outcomes. However, the lower threshold for normal weight (18.5 kg/m²) was primarily determined in the context of malnutrition, famine and low-resource settings. Therefore, applying WHO BMI thresholds to IVF populations may not fully capture the nuances relevant to reproductive health. Study design, size, duration Tri-continent retrospective cohort study of first-time IVF and ICSI cycles across three centers - ANDROFERT (Campinas, Brazil), Anatolia IVF (Ankara, Turkey), and IVFMD at My Duc Hospital (Ho Chi Minh City, Vietnam) between 2015 and 2017. Participants/materials, setting, methods Our study included 11,601 patients, of whom 10,443 had a normal BMI (18.5–25.0 kg/m²) according to WHO guidelines. Within this group, 2,406 patients had a low-normal BMI (18.5–19.99 kg/m²), while 8,037 had a BMI of 20.0–25.0 kg/m², referred to as “true-normal.” Additionally, 1,158 patients were classified as underweight, with a BMI below 18.5 kg/m². Main results and the role of chance Patients with a low-normal BMI were younger than those in the 20–25 kg/m² group and had higher AFC and AMH levels, as well as different sperm parameters (P < 0.001 for all). However, there were no significant differences in infertility duration, number of oocytes retrieved, fertilization rates, or the number of transferable embryos.Patients with a low-normal BMI had significantly lower live birth rates following a fresh embryo transfer than those with a BMI of 20.0–25.0 kg/m² (16.2%vs.20.1%,p<0.001). This difference remained significant after adjusting for confounding variables, including age, AFC, total gonadotropin dose, sperm count, and sperm motility (aOR:0.72-95%CI:0.62–0.82,p<0.001). Moreover, their cumulative delivery rate per aspiration was lower than that of the 20.0–25.0 kg/m² group (30.1%vs.31.7%; aOR:0.86-95%CI:0.77–0.97,p=0.01). The live birth rate (aOR:0.93-95%CI:0.75–1.15, p = 0.49) and cumulative delivery rate per aspiration (aOR:1.02-95%CI:0.86–1.20,p=0.86) did not differ between low-normal BMI patients and underweight patients. When comparing patients with a BMI of 20-25 kg/m² to all patients with a BMI under 20 kg/m², live birth rates were higher in the former (20.1%vs.16.9%, p < 0.01), and this difference remained significant after adjustment (aOR:0.80-95%CI:0.70–0.92,p=0.001). Similarly, the cumulative delivery rate per aspiration was higher in the 20-25 kg/m² group (31.7%vs.30.7%), with the difference remaining significant after adjustment (aOR:0.85-95%CI:0.77-0.94, p = 0.002). Limitations, reasons for caution Information on patients' overall health status and comorbidities, which may influence IVF outcomes, was unavailable. The lack of complete data on miscarriage rates is a limitation. Wider implications of the findings The threshold for adverse IVF outcomes appears to be BMI <20.0 kg/m² rather than the WHO-defined normal lower limit (18.5 kg/m²), as live birth and cumulative delivery rates decline in this range. This highlights the need for reproductive health-specific BMI categories which could enhance patient counseling and potentially enhance success. Trial registration number No
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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 teacher head, 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".