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

Introduction

Welcome from Tamara L. Wexler, MD, PhD

In this issue of EndoScan, we review a cross-section of topics related to the impact of weight on fertility.  Any of the topics covered in this issue could be the focus of its own in-depth review.

Over one-third of the adult U.S. population is obese.1 Media reports on the dangers of obesity abound, including its impact on the health of pregnant women and their children. In addition, there is evidence that obesity makes it more difficult to conceive, both spontaneously and via assisted reproductive technology (ART). We review studies examining the association between overweight/obesity and fecundity,2 ART outcomes ,3 and fertility in women with known polycystic ovary syndrome (PCOS),4 as well as general guidance from the American Society for Reproductive Medicine (ASRM) on weight and fertility.5,6

Obesity rates in children as well as adults remain high.1,7 One of our reviewed articles, by Jacobsen and colleagues, examines the relationship between adolescent or young adult weight and later fertility,8 noting the predictive value of being overweight—and of being underweight.

Less attention has been paid recently to the impact of low BMI on fertility; in addition to Jacobsen and colleagues’ epidemiologic study, we review an early paper suggesting that difficulties conceiving in even mildly underweight women may be solved by moderate weight gain .9

While this issue of EndoScan focuses on the effect of female BMI, male weight has also been shown to impact fertility.  Recent reviews and studies demonstrate an association between male BMI and sperm count,10,11 sperm quality,11,12 and other semen parameters.11 We will cover these issues in depth in the next issue of EndoScan.

Overweight
Excess weight is associated with reduced fertility.2,8,13,14 The exact mechanism by which obesity affects fertility is not clear, though various hypotheses have been proposed, including menstrual cycle irregularity, ovulatory dysfunction, or abnormal levels of insulin or other hormones.2,5

Gesink Law and colleagues demonstrate that the negative relationship between obesity (and to a lesser extent overweight) and fecundity holds true even when controlling for menstrual irregularities and smoking.2 The negative effect of weight on fertility may be most pronounced in time to first pregnancy.2,8 Even in women with known PCOS, increasing BMI appears to have a negative impact on fertility, as is reported in Legro and colleagues’ 2014 report from a large multicenter trial (the PPCOSII study).4 Studies also suggest that overweight/obesity negatively impacts in vitro fertilization (IVF) and other ART outcomes.3,15-18

The effect of weight loss
Most of the studies looking at weight and fertility are observational in nature; fewer studies have investigated the potential impact of weight loss on improving fertility.  In a small non-blinded 1995 study by Clark and colleagues, weight loss in obese women was found to restore fertility.19

Of those studies that examine the effect of weight loss on fertility in obese women, the majority focus on women with known PCOS or on women undergoing ART. In a prospective cohort study of 170 women undergoing assisted reproduction (233 ART cycles), short-term weight loss (average 3 kg)—particularly in women with higher baseline BMI—was associated with better oocyte retrieval, though not with a significant difference in clinical pregnancy or live birth.15

The method of weight loss may be important. One recent paper reported reduced oocyte retrieval and quality in women undergoing ART who had previously received bariatric surgery, compared to obese and normal-weight women with infertility.18 Other papers have cited bariatric surgery as improving fertility in young women by virtue of weight reduction and BMI achieved but not by surgical weight loss method used, or as reducing complications of pregnancy though with a potential increased risk for small-for-gestational-age neonates.20,21

As the U.S. population of overweight/obesity remains high,22 it is important not only to elucidate the mechanism by which weight interferes with conception, but also to define measures to improve fecundity. A study examining the impact of weight loss on conception—and of the method of weight loss, given the potentially confounding effects of vigorous exercise and bariatric surgery—would provide important data for managing obesity in women seeking fertility.

Underweight, and the impact of weight gain
In recent decades, less attention has been paid to the impact of being underweight. Results regarding the effect of low BMI on fertility differ, with many studies demonstrating that underweight makes conception more difficult,8,9,13,14,23, but others finding only borderline significance or a small effect, if any.

Jacobsen and colleagues’ retrospective population analysis of a large cohort of women showed significant effect of underweight at age 20 on later fertility (though not as strong as the effect of overweight in same group).6

Bates and colleagues demonstrate the impact of moderate weight gain in promoting spontaneous conception in mildly underweight women with unexplained infertility.9 In 26 women deemed mildly underweight (91% ideal body weight [IBW]) and with apparently normal menses but averaging >4 years of unexplained infertility, 73% were able to conceive after moderate weight gain via dietary program. While this is an early paper, and not a randomized controlled trial, it represents an interventional study in women who are mildly underweight, and suggests that weight gain alone may be sufficient to restore fertility.

The Jacobsen study used BMI as its measure of weight, and the 1982 Bates study used percent IBW (standard at the time).8,9 It may be that other measures, such as body fat, are more relevant in terms of fertility and pregnancy.  A certain amount of body fat is felt to be necessary to sustain a healthy pregnancy, and the same threshold may be important in becoming pregnant.

It is Important to Remember…
Of course, the impact of underweight and overweight on the health of any woman is of importance apart from fertility. While this EndoScan focuses on the impact of weight (underweight and overweight) on conceiving, it is important to note the potential impact of obesity on overall maternal and personal health. The 2008 ASRM educational bulletin we review provides an excellent resource for obesity and maternal health.5 To underscore that fertility itself is influenced by many factors unrelated to weight, we include its 2013 ASRM counterpart as a resource on fertility in general.6

Key points

  • Extremes of weight are associated with reduced fertility. Since a higher percentage of U.S. women are overweight/obese than are underweight,23,24 the population effect of high BMI is greater.
  • Being overweight or obese has a negative impact on fecundity, including in women with known PCOS.  Weight loss likely improves fertility, though the method of weight loss may be important.
  • Being underweight makes it more difficult to conceive, perhaps due the lack of sufficient body fat. Gaining even a small amount of weight may be sufficient for conception.
  • Weight at late adolescence/early adulthood may predict fertility in later adult life.
  • As the U.S. population of overweight/obesity remains high,1,7,23 it is important to elucidate the mechanism by which weight interferes with conception—and to define measures to improve fecundity.
  • Randomized trials investigating the impact of weight loss on conception in overweight/obese individuals would provide important data.

 

References

  1. Ogden CL, Carroll MD, Kit BK, Flegal KM. Prevalence of childhood and adult obesity in the United States, 2011-2012. JAMA. 2014;311(8):806-814.
  2. Gesink Law DC, Maclehose RF, Longnecker MP. Obesity and time to pregnancy. Hum Reprod. 2007;22(2):414-420.
  3. Pinborg A, Gaarslev C, Hougaard CO, et al. Influence of female bodyweight on IVF outcome: a longitudinal multicentre cohort study of 487 infertile couples. Reprod Biomed Online. 2011;23(4):490-499.
  4. Legro RS, Brzyski RG, Diamond MP, et al. The Pregnancy in Polycystic Ovary Syndrome II study: baseline characteristics and effects of obesity from a multicenter randomized clinical trial. Fertil Steril. 2014;101(1):258-269.
  5. Practice Committee of American Society for Reproductive Medicine. Obesity and reproduction: an educational bulletin. Fertil Steril. 2008;90(5 Suppl):S21-29.
  6. Practice Committee of American Society for Reproductive Medicine in collaboration with Society for Reproductive Endocrinology and Infertility. Optimizing natural fertility: a committee opinion. Fertil Steril. 2013;100(3):631-637.
  7. Skinner AC, Skelton JA. Prevalence and trends in obesity and severe obesity among children in the United States, 1999-2012. JAMA Pediatr. 2014 Apr 7. doi: 10.1001/jamapediatrics.2014.21. [Epub ahead of print]
  8. Jacobsen BK, Knutsen SF, Oda K, Fraser GE. Body mass index at age 20 and subsequent childbearing: the Adventist Health Study-2. J Womens Health (Larchmt). 2013;22(5):460-466.
  9. Bates GW, Bates SR, Whitworth NS. Reproductive failure in women who practice weight control. Fertil Steril. 1982;37(3):373-378.
  10. Sermondade N, Faure C, Fezeu L, et al. BMI in relation to sperm count: an updated systematic review and collaborative meta-analysis. Hum Reprod Update. 2013;19(3):221-231.
  11. Eisenberg ML, Kim S, Chen Z, Sundaram R, Schisterman EF, Buck Louis GM. The relationship between male BMI and waist circumference on semen quality: data from the LIFE study. Hum Reprod. 2014;29(2):193-200.
  12. Hammiche F, Laven JS, Twigt JM, Boellaard WP, Steegers EA, Steegers-Theunissen RP. Body mass index and central adiposity are associated with sperm quality in men of subfertile couples. Hum Reprod. 2012;27(8):2365-2372.
  13. Rich-Edwards JW, Spiegelman D, Garland M, et al. Physical activity, body mass index, and ovulatory disorder infertility. Epidemiology. 2002;13(2):184-190.
  14. Davies MJ. Evidence for effects of weight on reproduction in women. Reprod Biomed Online. 2006;12(5):552-561.
  15. Chavarro JE, Ehrlich S, Colaci DS, Wright DL, Toth TL, Petrozza JC, Hauser R. 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.
  16. 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.
  17. 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.
  18. 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.
  19. Clark AM, Ledger W, Galletly C, et al. Weight loss results in significant improvement in pregnancy and ovulation rates in anovulatory obese women. Hum Reprod. 1995;10(10):2705-2712.
  20. Musella M, Milone M, Bellini M, Sosa Fernandez LM, Leongito M, Milone F. Effect of bariatric surgery on obesity-related infertility. Surg Obes Relat Dis. 2012;8(4):445-449.
  21. Sheiner E, Willis K, Yogev Y. Bariatric surgery: impact on pregnancy outcomes. Curr Diab Rep. 2013;13(1):19-26.
  22. National Center for Health Statistics. NCHS Data on Obesity. February 2012. http://www.cdc.gov/nchs/data/factsheets/factsheet_obesity.htm. Accessed May 5, 2014.
  23. Centers for Disease Control and Prevention. Adult Obesity Facts. March 28, 2014. http://www.cdc.gov/obesity/data/adult.html. Accessed May 5, 2014.
  24. Fryar CD, Ogden CL. NCHS Health E-Stat. Prevalence of Underweight Among Adults Aged 20 Years and Over: United States, 1960–1962 Through 2007–2010. http://www.cdc.gov/nchs/data/hestat/underweight_adult_07_10/underweight_adult_07_10.htm. Accessed May 5, 2014.
First Article:
Obesity Reduces Fecundity Regardless of Menstrual Cycle Regularity or Smoking Status
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