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Elevated body mass index in modified natural cycle frozen euploid embryo transfers is not associated with live birth rate

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Abstract

Purpose

To assess the impact of elevated BMI on the success of modified natural cycle frozen embryo transfers (mNC-FET) of euploid embryos.

Methods

This retrospective cohort study at a single academic institution reviewed mNC-FET involving single euploid blastocysts from 2016 to 2020. Comparison groups were divided by pre-pregnancy BMI (kg/m2) category: normal weight (18.5–24.9), overweight (25–29.9) or obese (≥ 30). Underweight BMI (< 18.5) was excluded from the analysis. The primary outcome was live birth rate (LBR) and secondary outcome was clinical pregnancy rate (CPR), defined as presence of fetal cardiac activity on ultrasound. Absolute standardized differences (ASD) were calculated to compare descriptive variables and p-values and multivariable logistic regressions with generalized estimating equations (GEE) were used to compare pregnancy outcomes.

Results

562 mNC-FET cycles were completed in 425 patients over the study period. Overall, there were 316 transfers performed in normal weight patients, 165 in overweight patients, and 81 in obese weight patients. There was no statistically significant difference in LBR across all BMI categories (55.4% normal weight, 61.2% overweight, and 64.2% obese). There was also no difference for the secondary outcome, CPR, across all categories (58.5%, 65.5%, and 66.7%, respectively). This was confirmed in GEE analysis when adjusting for confounders.

Conclusion

While increased weight has commonly been implicated in poor pregnancy outcomes, the effect of BMI on the success of mNC-FET remains debated. Across five years of data from a single institution using euploid embryos in mNC-FET cycles, elevated BMI was not associated with reduced LBR or CPR.

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Notes

  1. A 2000 World Health Organization (WHO) statement suggested that overweight should be defined as BMI > 23 and obesity defined as > 25 in an Asian population[18]; however, in a 2004 statement, the WHO indicated that a range of plausible BMI cut points exist and that “it would not be possible define a single set of cut points in these populations” [19]. As different guidelines continue to be proposed, the 2000 cut-offs were used for standardization in this paper.

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Funding

This research was supported in part by the TADA-BSSR training grant from the NIH National Heart, Lung, and Blood Institute (NHLBI, grant number 1T32HL151323).

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Authors and Affiliations

  1. Department of Obstetrics & Gynecology, Stanford Hospital, Center for Academic Medicine, MC 5317, 453 Quarry Road, Palo Alto, CA, 94304, USA

    Isabel Beshar & Wendy Y. Zhang

  2. Division of Reproductive Endocrinology & Infertility, Department of Obstetrics & Gynecology, Stanford University, 1195 W Fremont Avenue, Sunnyvale, CA, 94087, USA

    Amin A. Milki & Brindha Bavan

  3. Department of Epidemiology & Population Health, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA, 94305, USA

    Rebecca M. Gardner

  4. Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine, Weill Cornell Medicine, 1305 York Avenue, 6th Floor, New York, NY, 10021, USA

    Jasmyn K. Johal

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  1. Isabel Beshar
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Correspondence to Isabel Beshar.

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Brindha Bavan, MD, is a clinical research consultant for Stanford Atropos Health.

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Beshar, I., Milki, A.A., Gardner, R.M. et al. Elevated body mass index in modified natural cycle frozen euploid embryo transfers is not associated with live birth rate. J Assist Reprod Genet 40, 1055–1062 (2023). https://doi.org/10.1007/s10815-023-02787-y

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