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Effect of Obesity on Fertility


Body mass index (BMI) is quotient of the weight of individual expressed in kilogram (kg) and height in metres square (m2). Universally, BMI is used in medicine for showing pathology in body mass of the human (Eknoyan, 2008). The percentage of obese people in developing countries has increased 3 times over the past 20 years (Hossain et al., 2007). There were 1.6 billion overweight people worldwide and from that 400 million were obese. BMI usually closely related to human body function.

Classes of BMI

There are 6 Classes of BMI which are:

  1. Underweight (<18.5 kg/m2)
  2. Normal (18.5-24.99 kg/m2)
  3. Overweight (25-29.99 kg/m2)
  4. Obesity Type I (30-34.99 kg/m2)
  5. Obesity Type II (35-39.99 kg/m2)
  6. Morbid Obesity (>39.99 kg/m2)

Relationship between BMI and Fertility

Most obese women are not infertile; however, obesity and its negative impact upon fecundity and fertility are well documented. Obese women are three times more likely to suffer infertility than women with a normal body mass index (Rich-Edwards et al. 1994). Obese women experience impaired fecundity both in natural and assisted conception cycles (Zaadstra et al. 1993, Crosignani et al. 1994). The mechanism through which its effect is exerted is more controversial. It has been proposed that obesity impairs fertility through an effect upon the control of ovulation, oocyte development, embryo development, endometrial development, implantation and pregnancy loss. Obese women, particularly those with central obesity, are less likely to conceive per cycle. Obese women suffer perturbations to the hypothalamic–pituitary–ovarian axis, menstrual cycle disturbance and are up to three times more likely to suffer anovulation. A fine hormonal balance regulates follicular development and oocyte maturation, and it has been observed that obesity can alter the hormonal milieu. Leptin, a hormone produced by adipocytes, is elevated in obese women, and raised leptin has been associated with impaired fecundity. Obesity impairs ovulation but has also been observed to detrimentally affect endometrial development and implantation (Brewer & Balen, 2010).

Public Awareness

Obesity is an increasingly prevalent health burden upon modern society. Survey done by Ministry of Health show number of adults with overweight problem increased from 16.6% (1.7million) in year 1996 to 27% (4.2million) in year 2003. Survey in 2006 follow the same trend as overweight adults increased to 43.1%.National Health and Morbidity survey 2011,33.6% adults age 18 years above were overweight and 19.5% were obese. Increasing number of adults with weight management issue showed our society lack in awareness of their health.


Studies have shown that BMI is correlated to more direct measures of body fat. Adults with BMI more than 25 kg/m2 are consider overweight and morbid obesity when BMI more than 39.99 kg/m2. Obese people usually easily get tired, less energetic and having extra fat around the waist. Besides BMI, Waist measurement helps to screen for the possible health risk related to overweight and obesity in adults. If most of fat is around waist rather than hip, there is increased risk for coronary heart disease and diabetes type 2.

Epidemiology and Success Rate

Increased obesity rates among pregnant women are a significant public health concern. In pregnancy, increasing BMI may cause various implications for prenatal care and supervision of delivery. Obese pregnant women face high risk of pregnancy complication like pre-eclampsia, eclampsia, pre- and post-term delivery, induction of labor, macrosomia, increased rate of caesarean section, and post-partum hemorrhage (Vellanki, 2012). A survey of studies reporting the effect of obesity upon ART outcome reveals inconsistent findings, although study design and definition of obesity are variable. However, the majority of the studies suggest that obesity has a deleterious effect upon ART. Obesity has been reported to affect ovarian stimulation in women undergoing treatment. Reported effects include prolonged ovarian stimulation, increased dose requirement of gonadotrophin, increased incidence of follicular asynchrony and increased cancellation rates (Mulders et al. 2003, van Swieten et al. 2005, Balen et al. 2006, Bellver et al. 2006, Maheshwari et al. 2007, Esinler et al. 2008). Obese women undergoing IVF/ICSI have lower live birth rates. It is thought that this is the cumulative effect of lower implantation and pregnancy rates, higher miscarriage rates and increased obstetric complications (Bellver et al. 2006). Whilst some authors have reported lower pregnancy and live birth rates in obese women undergoing assisted conception treatments (Wang et al. 2000, Bellver et al. 2010). Weight loss improves reproductive function in overweight and obese women (Clark et al. 1995, 1998, Crosignani et al. 2003, Tang et al. 2006). One must be careful not to promote extreme rapid dieting and acute very low calorie diets, as these have been associated with poor ART outcomes (Tsagareli et al. 2006). It is advisable for patients to aim for a normal BMI prior to commencing fertility treatment. Indeed, these guidelines recommend deferring any treatment until a woman’s BMI <35 kg/m2, and recommending that BMI <30 kg/m2 is preferable (Balen & Anderson 2007). In summary, obesity has been observed to impair both natural and assisted conception.


Active strategies for weight control and life style advice is needed for the management of obesity. It is recommended that all obese women who planning pregnancy to have sensible weight reduction, including healthy diet, exercise and referral to a dietician where appropriate.


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Last Reviewed : 14 April 2016
Writer : En. Mohd Nur Muhaimin Adli Ishak
Accreditor : En. Krishnan A/L Kanniah