Neutral effect of body mass index on implantation rate after frozen-thawed blastocyst transfer

Compared with normal weight women, overweight women with body mass indexes of 25–29.9 kg/m2 have similar implantation and live-birth rates after frozen-thawed blastocyst transfer.

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Volume 108, Issue 5, Pages 770–776.e1

Authors:

Iris G. Insogna, M.D., Malinda S. Lee, M.D., M.B.A., Rebecca M. Reimers, M.D., M.P.H., Thomas L. Toth, M.D.

Abstract:

Objective

To examine the effects of body mass index (BMI) on implantation rate after uniform protocol frozen-thawed blastocyst transfer in women with a homogenous uterine environment.

Design

Retrospective cohort study.

Setting

Single IVF clinic at a large academic institution.

Patient(s)

Four hundred sixty-one infertile women treated at a large academic institution from January 2007 to January 2014.

Intervention(s)

All women underwent standardized slow frozen-thawed blastocyst transfers with good-quality day 5–6 embryos, following an identical hormonal uterine preparation, with comparison groups divided according to BMI category: underweight (<18.5 kg/m2), normal weight (18.5–24.9 kg/m2), overweight (25.0–29.9 kg/m2), and obese (≥30.0 kg/m2).

Main Outcome Measure(s)

Implantation rate.

Result(s)

There were no statistically significant differences identified when comparing implantation rates among the four BMI cohorts. The implantation rate was 38.2% in normal weight patients, 41.7% in underweight patients, 45.1% in overweight patients, and 34.7% in obese patients. Adjusted odds ratios (OR) demonstrated no association between the main outcome, implantation rate, and BMI. Compared with the normal weight patients, the adjusted OR of implantation was 1.70 (95% confidence interval [CI], 0.40–7.72) for underweight patients, 1.61 (95% CI, 0.97–2.68) for overweight patients, and 0.92 (95% CI, 0.49–1.72) for obese patients. Secondary outcomes, including rates of miscarriage, clinical pregnancy, ongoing pregnancy, and live birth, were not significantly different between cohorts. While powered to detect a 16% difference between overweight and normal weight women, the study was underpowered to detect differences in the underweight and obese women, and no definitive conclusions can be drawn for these small cohorts. Patients with transfers that required the longest amount of time, greater than 200 seconds, had the highest average BMI of 27.5 kg/m2.

Conclusion(s)

Under highly controlled circumstances across 7 years of data from a single institution, using a uniform uterine preparation, following a precise transfer technique with high-quality day 5–6 slow frozen-thawed blastocysts, a BMI in the overweight range of 25–29.9 kg/m2 is not associated with a poorer implantation rate or live-birth rate, nor is it associated with an increased risk of miscarriage when compared with a normal BMI range. The increased length of time required during transfer for women with higher BMI suggests body habitus may contribute to difficult transfers, although this may not translate into poorer implantation rates. By using a standardized protocol for slow freezing and thawing of embryos, using identical hormonal preparation and a uniform ET protocol, a homogenous uterine environment was created in this carefully selected cohort of women, thereby minimizing confounders and uniquely highlighting the neutral effect of overweight BMI on implantation rate.


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Fertility and Sterility

Editorial Office, American Society for Reproductive Medicine

Fertility and Sterility® is an international journal for obstetricians, gynecologists, reproductive endocrinologists, urologists, basic scientists and others who treat and investigate problems of infertility and human reproductive disorders. The journal publishes juried original scientific articles in clinical and laboratory research relevant to reproductive endocrinology, urology, andrology, physiology, immunology, genetics, contraception, and menopause. Fertility and Sterility® encourages and supports meaningful basic and clinical research, and facilitates and promotes excellence in professional education, in the field of reproductive medicine.

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