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Can BMI Affect the Success of Fertility Treatments?

V.A. Moragianni, S.M. Jones, D.A. Ryley

July 10, 2017
Emma Holt

Body Mass Index and Assisted Reproductive Technology Cycles

Body mass index – more commonly known as BMI – is a health metric used by doctors to classify a person’s weight into different categories including underweight, normal weight, overweight, and obese. How does BMI affect the outcome of use of assisted reproductive technology?  A team of medical doctors endeavored to study this question by investigating the outcomes of first assisted reproductive technology cycles (a.k.a. first fertility treatments) in individuals with varying body mass indices. 

The Research: Background

The study entitled “The effect of body mass index on the outcomes of first assisted reproductive technology cycles” was published by a team of three medical doctors in the journal Environment and Epidemiology in 2012.  Aware that obesity was an ongoing, global epidemic that impacted patient health and wellness, the researchers endeavored to investigate the effect, if any, obesity had on fertility treatments.  As the authors state, and as many of you may well already know, obesity had been linked to coronary artery disease, hypertension, and diabetes.  But did you know that obesity can negatively impact a woman’s reproductive function through its impacts on menstruation? 

Put simply, obesity is thought to be a cause of menstrual dysfunction, which in turn can lead to oligomenorrhea, anovulation, and dysfunctional uterine bleeding.  The authors additionally report that previous research has shown fecundity to be reduced in populations of both overweight and obese individuals.  Furthermore, past research referenced by the authors reportedly shows that high rates of pregnancy obesity can increase the likelihood of pregnancy complications such as increased rates of gestational hypertension, preeclampsia, gestational diabetes, postpartum hemorrhage, and fetal macrosomia.  In this past research cited by the authors, obese women were also found to have higher rates of labor induction and operative delivery (C-section).

There has been debate in the scientific literature about the effects of obesity on patients undergoing fertility treatments; such debate has focused upon response to treatment and success rates.  With this background knowledge in mind, the authors of this study set out to investigate the relationship between obesity and first assisted reproductive technology (ART) outcomes in women undergoing their first in vitro fertilization (IVF) or IVF-intracytoplasmic sperm injection (ICSI) cycle at a single medical institution.  The researchers placed a special emphasis on live birth outcome data, but also collected data regarding the quality of the patients’ embryos, age of both partners, baseline FSH (gonadotropin), duration of stimulation in days, total gonadotropin dose used, peak serum estradiol levels, number of oocytes retrieved, use of ICSI, day of embryo transfer, and number of embryos transferred.

Who did the researchers study?

The research was conducted via a retrospective chart review.  This means that rather than following women in the present day who underwent the fertility treatments of interest, the researchers reviewed medical charts from past patients at the medical center – Boston IVF –where the study was conducted.  Patients who underwent ART cycles from January 1, 2004 to December 21, 2010 were included in the study if they were within the age range of 20 to 47 years old, they were having their first IVF or IVF-ICSI cycle using their own oocytes, and had a BMI recorded in their electronic medical chart.  The total number of patients retrospectively studied was 4,609.  The patient population was stratified by the most recent (at the time) classification of BMI categories employed by the World Health Organization.  The below table demonstrates the BMI categories that the researchers used to stratify the individuals under investigation:

What did the researchers find?

Compared to women from the Normal category, patients from Obese Classes II and III had statistically lower baseline serum FSH (gonadotropin) values.  Patients from Obese Classes I and II were found to have statistically lower peak serum estradiol levels and to require higher daily gonadotropin doses.  ICSI was found to be used in statistically higher frequency with underweight, overweight, and obese patients.  What does “statistically higher” or “statistically lower” mean?  These terms refer to the use of statistics to put the study’s results into numbers.  When something is stated to be “statistically” higher/lower, that means that the statistical calculations for that factor indicated a difference between the measurements from the different categories that was found to be “important.”  As BMI increased, researchers also report that more Day 3 than blastocyst transfers were had by the patients. 

No statistically significant differences existed across BMI categories relating to cycle cancellation, spontaneous abortion, biochemical pregnancy, ectopic pregnancy or multiple births.  Statistical significance, biological significance, and even personal significance are all different, however.  Although no statistical differences were found for these factors across BMI categories, it is valuable to note that odds of spontaneous abortion, biochemical pregnancy, ectopic pregnancy, and multiple births all tended to increase with increasing BMI.  In further negative news, odds of implantation, clinical pregnancy, and live births were significantly lower for obese patients in all classes (I, II, and III) than for the individuals from the Normal category.  Odds of global miscarriage (biochemical pregnancy and spontaneous abortions) were significantly higher for Obese Class III patients (only) than Normal Class patients.  In numbers, adjusted odds of live birth dropped 37% for Obese Class I individuals, 61% for Obese Class II individuals, and 68% for Obese Class III individuals compared to Normal Class patients.  It was determined that, after their first fresh IVF cycle, underweight, normal-weight, and overweight patients all have similar odds of live birth.


It is of value to note that although these researchers found decreased odds of live birth for obese patients, the odds of live birth for obese patients were NOT zero.  The fact that the study investigated such a large number of women at one institution where treatment was standardized helped to strengthen the study’s results.  However, as the authors suggest, the retrospective nature of the study made it impossible for researchers to consider lifestyle characteristics of the women they studied, such as smoking or drinking habits.  The researchers were only able to base their conclusions upon data from medical charts at one institution, not upon how the women lived their daily lives.  The authors also mention that their investigation of the first ART cycle could fail to account for the fact that obese women sometimes need higher doses of medication to find success with a treatment; such higher dosages and successes would not be seen until later ART cycles.  It is stated by the authors that weight loss has potential to optimize ART cycle success, but that is likely not the only factor that contributes to ART cycle success. 

Do not be discouraged by this scientific research, for every individual’s body is different and has the potential to react differently to different treatments.  Your doctor should be able to best advise you on the treatments you can explore and the actions you can take if you are seeking to begin fertility treatments.  You may choose to use the information discussed in this blog to discuss your treatment plan with your doctor.  The information provided here is meant to empower you and inform you about the research done regarding fertility so you can have discussions with your doctor and advocate for yourself, it is not meant to serve as a medical recommendation.  Please always consult your doctor prior to deciding on a treatment plan that will be the best for you and your body.

Stay informed, stay empowered, and good luck on your journey.


The effect of body mass index on the outcomes of first assisted reproductive technology cycles

Fertility and Sterility - July 2012, Volume 98, Issue 1, Pages 102–108


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