Weight and Fertility: A Review
May 2014
Volume 5, Issue 2

Increasing BMI Lowers Likelihood for Successful In Vitro Fertilization

Reprod Biomed Online. 2011;23(4):490-499

Introduction: This study was designed to investigate whether a woman’s body mass index affected the likelihood for pregnancy after assisted reproductive therapy (ART).

Methods: Outcome of in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) was assessed in 487 women over a 5-year period. The women underwent a total of 1,417 treatment cycles. Approximately 21% of the women were overweight (BMI 25–29.9 kg/m2) and 12% were obese (BMI ≥30 kg/m2).

Results: Per-cycle outcomes showed that BMI was linked to greater number of initiated cycles/woman (P=0.01), number of cancelled cycles/woman (P<0.01) and the total dose of gonadotrophin used/cycle (P<0.01). The most common reason for cancelling a cycle was “no fertilization” in the obese group compared with “poor ovarian response” in the normal-weight group.

In addition, obese women had a lower ongoing pregnancy rate (defined as least one fetus with fetal heartbeat verified by ultrasound in week 7) per cycle than normal-weight women (20.8% versus 28.3%; P=0.04). The live-birth rate per cycle also was lower among obese women compared with normal-weight women, although the difference did not reach statistical significance (15.2% versus 21.5%; P=0.06). By multilevel logistic regression analysis, performed on data from all treatment cycles, women’s BMI was significantly associated with a decreased likelihood for a first live birth using IVF (P=0.034). Other significant negative predictors of live births included increasing age among the women as well as among their male partners (P=0.037 and P=0.040, respectively).

The researchers also examined characteristics of only the first cycle of fresh IVF or ICSI to eliminate the probability of a pregnancy occurring after repeated treatment cycles in the same couple. This analysis showed a negative linear association between BMI and the number of retrieved oocytes (P<0.001), while an inverse U-shaped relationship was found between BMI and the number of developed embryos, with underweight and obese women having less embryos available (P=0.03). In addition, increasing BMI was linked to decreasing number of cycles resulting in positive serum human chorionic gonadotrophin (HCG; P<0.01).

Conclusion: The authors concluded that women who are obese are at a disadvantage when undergoing fertility treatments and should be counseled on the potential negative effects of obesity on pregnancy outcomes and general health. The authors also suggested that weight loss should be encouraged in overweight and obese women undergoing fertility treatments.


Tamara L. Wexler, MD, PhD, is an endocrinologist specializing in reproductive and neuroendocrinology, and an Attending in Medicine, Massachusetts General Hospital, Boston, MA.

This study was designed to measure the impact of female BMI on first assisted reproduction treatment (ART) outcomes after consecutive cycles; ART included IVF with partner or donor sperm, intracytoplasmic sperm injection (ICSI), and frozen-embryo transfer. The participating 487 couples were drawn from fertility clinics in Denmark. Female and male age average were approximately 32 years and 34.5 years, respectively. The average number of reported infertile years ranged from 3.9-4.7—slightly greater in underweight women, and particularly in obese women where it reached statistical significance (P=0.04). Outcome measures included (but were not limited to) number of oocytes retrieved, number of developed embryos, pregnancy, and live birth.

Female BMI was inversely related to number of oocytes retrieved—the more overweight the woman, the fewer the oocytes retrieved. Of note, both overweight and underweight had a negative impact on the number of developed embryos per IVF cycle. The reported inverse relationship between BMI and (+) HCG suggests that clinical pregnancy is less frequent in overweight/obese women undergoing IVF. The effect of weight on pregnancy was most notable at younger ages (<25 years), and the effect was no longer statistically significant after age 36.

Overall, live birth was negatively impacted by female BMI as well as by male and female age. However, female weight did not reach statistical significance as a predictor of live birth per cycle (P=0.06); it is possible that in a larger cohort of women, the rate of live births would reach significance. [Comparing only the first cycle of IVF or ICSI in normal-weight (n=75) and obese (n=10) women, live birth rates were 24.6% and 16.9%, but did not reach statistical significance.]

Limitations include a different distribution of diagnosed cause of infertility among women in different BMI groups. A portion of information was gathered by questionnaire (64% response rate for baseline and 1 year), opening the results to selection bias. In addition, a third of files did not include female BMI information. As only baseline BMI data was gathered, weight changes over the study period were not included. The number of women who may have had concomitant PCOS is unknown. While male age was recorded (and found to predict live birth), male BMI was not included in the analysis.

This is not the only study to report poorer ART results at higher weight.1-3 In a retrospective cohort study, Bellver and colleagues reported that female BMI was inversely related to pregnancy and live birth rates, hypothesizing that uterine receptivity was responsible.2

While the authors suggest weight loss for women prior to undergoing ART, this study did not include intervention. There are some—but few—studies of the impact of weight loss on clinical outcomes in ART. In a prospective cohort study of 170 women undergoing ART (233 cycles), Chavarro and colleagues found that both baseline BMI and short-term weight loss were associated with reproductive outcomes.3 Women who lost weight (average 3 kg), particularly those with higher baseline BMI, had more metaphase II oocytes retrieved, though no significant difference in clinical pregnancy or live birth rates was found.

Last month, a study in Obesity suggested that bariatric surgery for weight loss may have a negative impact on ART success;4 women who had undergone bariatric surgery had fewer oocytes retrieved than obese or normal-weight women with infertility. While differences between the study groups suggest further research is needed, it is important to note that the method of weight loss may itself impact fertility in some cases.

1. Rittenberg V, Seshadri S, Sunkara SK, Sobaleva S, Oteng-Ntim E, El-Toukhy T. Effect of body mass index on IVF treatment outcome: an updated systematic review and meta-analysis. Reprod Biomed Online. 2011;23(4):421-439.

2. Bellver J, Pellicer A, García-Velasco JA, Ballesteros A, Remohí J, Meseguer M. Obesity reduces uterine receptivity: clinical experience from 9,587 first cycles of ovum donation with normal weight donors. Fertil Steril. 2013;100(4):1050-1058.

3. Chavarro JE, Ehrlich S, Colaci DS, et al. Body mass index and short-term weight change in relation to treatment outcomes in women undergoing assisted reproduction. Fertil Steril. 2012;98(1):109-116.

4. Christofolini J, Bianco B, Santos G, Adami F, Christofolini D, Barbosa CP. Bariatric surgery influences the number and quality of oocytes in patients submitted to assisted reproduction techniques. Obesity (Silver Spring). 2014;22(3):939-942.

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Body Mass Index in Young Adulthood Linked to Increased Risk of Nulliparity
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