General Information
Body Mass Index (BMI) is an approximate measure of whether someone is underweight, healthy weight or overweight. It is calculated by dividing weight in kilograms by height in metres squared [1]
BMI does not perfectly correlate with fat mass. However, it gives an idea of disease risk [1]
BMI is divided into four categories:
Less than 18.5 kg/㎡ is underweight
18.5 to 24.9 kg/㎡ is healthy weight
More than 25 kg/㎡ is overweight
More than 30 kg/㎡ is obese
Waist-to-hip ratio (WHR) can be used in conjunction with BMI to determine abdominal adiposity and the risk of type 2 diabetes, cardiovascular disease and reproductive function issues including ovarian and testicular cancers. WHR is calculated by (waist measurement in cm ÷ hip measurement in cm) [1]
To decrease disease risk and subfertility, the ideal waist circumference and waist to hip ratios are:
Men’s ideal waist circumference is 85cm or less and WHR = 0.9 or less
Women’s ideal waist circumference is 80cm or less and WHR = 0.7 or less
The World Health Organization estimates 39% of adults worldwide are overweight, and 13% are obese [2]
Of those overweight, 39% are men and 40% are women [2]
Of those obese, 11% are men and 15% are women [2]
Over 340 million children worldwide, aged 5-19 years, are overweight or obese [2]
41 million children worldwide, under the age of 5, are overweight or obese [2]
For women of a healthy weight, weight gain of 11.5 to 16 kg during pregnancy is recommended.
For women overweight, weight gain of 5 to 11.5 kg during pregnancy is suggested. However, the recommendation is to optimise weight prior to becoming pregnant to reduce complications [3]
Overweight and obese adults are at an increased risk of developing type 2 diabetes mellitus, high blood pressure, cardiovascular disease, metabolic syndrome, pancreatitis, and musculoskeletal diseases [4]
Infertility in overweight and obese men
Increased weight in males disrupts hormones and increases inflammation in the body, leading to infertility [5]
Excess weight impairs sperm production, size and shape and ability to swim effectively, leading to infertility [5]
Increased weight affects hormone levels which decreases the production of testosterone from Leydig cells in the testes. The number of sperm is reduced, their ability to swim is decreased, and their size and shape are abnormal – therefore inhibiting the sperm’s ability to fertilize an egg [5]
Excess weight increases oxidative stress which decreases sperm quality [6]
Excess weight upregulates expression of the hormone Ghrelin. This inhibits testicular function, causing poor sperm health and infertility [7]
Overweight and obese men have increased heat around the testes. This induces oxidative stress and damaged sperm [8]
Infertility in overweight and obese women
Excess weight disrupts hormone levels resulting in ovulation problems [9]
Excess weight increases the risk of miscarriage, gestational diabetes and stillbirth [9,10]
Obese women with a history of unexplained recurrent miscarriages have a 73% increased risk of experiencing another miscarriage [10]
Obesity increases the risk of Gestational Diabetes, a condition that affects around 14% of pregnant women worldwide [11]
Gestational Diabetes increases the risk of preterm and cesarean delivery, and giving birth to a large baby. This increases the child’s risk of obesity, heart disease and blood sugar problems [11]
Excess weight in women with Polycystic Ovarian Syndrome (the leading cause of infertility among women of reproductive age) impairs ovulation and conception chances [9]
Overweight and obese women require higher doses of hormones, have fewer oocytes retrieved and have increased cycle cancellation rates when undergoing Assisted Reproductive Therapies. This reduces the chance of successful conception even through ICSI or IVF [12]
There is good news!
Losing weight regulates the menstrual cycle and can restore ovulation. This directly increases a couple’s chances of conception and taking home a healthy baby [13].
Weight loss of 10% body weight for women over 100 kg can restart ovulation. Even a 5 kg loss increases the chance of giving birth to a baby by 61.9% [13].
The closer to your ideal weight when trying to conceive, the better your chances of taking home a healthy baby when all major factors impacting conception in a couple’s case are taken into consideration.
Impact of maternal weight on foetal development
Obesity increases the risk of stillbirth and miscarriage [10]
Obese women have a 37% increased risk of miscarriage [14]
Obese women with poor blood sugar control (as seen in diabetes) have a 4-fold increased risk of miscarriage [15]
Maternal obesity increases the risk of a child developing neural tube defects and structural heart defects 3-fold [16]
Folic acid supplementation is less effective in preventing neural tube defects in obese women [16]
Maternal overweight and obesity increases a prospective child’s risk of asthma. Gaining more than 25 kg during pregnancy increases inflammation in the child’s airways, causing asthma by 9 years of age [17, 18]
Excessive weight gain during pregnancy increases a prospective child’s risk of obesity. This increases their risk of chronic diseases later in life [19]
References:
[1] http://apps.who.int/iris/bitstream/handle/10665/44583/9789241501491_eng.pdf?sequence=1
[2] http://www.who.int/mediacentre/factsheets/fs311/en/
[3] https://www.betterhealth.vic.gov.au/health/healthyliving/pregnancy-and-diet
[4] https://www.iasj.net/iasj?func=fulltext&aId=64666
[5] https://www.ncbi.nlm.nih.gov/pubmed/22693175/
[6] https://www.ncbi.nlm.nih.gov/pubmed/14511216/
[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4464503/
[8] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4492061/
[9] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4456969/
[10] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3515955/
[11] http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD009021.pub2/full
[12]https://www.researchgate.net/publication/233740615_Impact_of_overweight_and_underweight_on_assisted_reproduction_treatmen
[13] https://www.ncbi.nlm.nih.gov/pubmed/28739335?dopt=Abstract
[14] https://www.fertstert.org/article/S0015-0282(07)01525-7/fulltext
[15] https://academic.oup.com/humrep/article/19/7/1644/2356447
[16] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5096465/
[17] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5695645/
[18] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3735244/
[19] https://www.ncbi.nlm.nih.gov/pubmed/29421859
