When ‘Project Baby’ is in the offing, body weight takes on a new meaning. But the focus here is on healthy weight not ‘operation Size Zero’! This article explores the connection between obesity and its impact on fertility.

Overweight and obesity at a glance

Is your weight healthy for someone of your height? The best way to find out is to do a body composition analysis to determine your body fat percent. However the Body Mass Index (BMI) can help you figure this out. It is calculated as follows:

BMI = WEIGHT (kg) / HEIGHT (m) x HEIGHT (m)

Interpreting your BMI
Optimal weight range: BMI between 18.5 and 24.9kg/m2
Overweight: BMI above 24.9kg/m2
Obese: BMI above 30kg/m2

Excess body weight adversely affects fertility

Although you need some body fat for ovulation, you can have too much of a good thing: studies show that as BMI increases, the chances that a woman will conceive decrease drastically.

For instance, compared to women with a BMI below 30kg/m2, women with a BMI of 35kg/m2 or more were 26% less likely to get pregnant. And those with a BMI equal to or above 40kg/m2 were 43% less likely to achieve a spontaneous pregnancy.

Obesity hinders ovulation

Obesity affects ovulation by causing mayhem among the reproductive hormones. Scientists speculate that excess body fat disrupts the menstrual cycle and hampers ovulation via the following mechanisms:

  • Obesity is associated with elevated levels of insulin, which leads to a reduction in the synthesis of sex hormone-binding globulins (SHBG). Low levels of SHBG cause a surge in the level of free sex steroids such as testosterone.
  • The hormone oestrogen is produced mostly by the ovaries and in less important amounts by the adrenal glands and fat cells. Hence, if a woman has excessive body fat, there will be an oversupply of oestrogen.

The high levels of free sex steroids and/or oestrogen signal the brain to stop stimulating the development of follicles — sac like structures needed for the eggs to mature and develop — and, thus, ovulation does not occur. No ovulation, no pregnancy.

Obesity thwarts fertilisation

Not all obese women face ovulation issues. However, even among obese women who ovulate, the chances of conceiving are low. Why? Well, in a nutshell, it appears that obese individuals have elevated levels of the hormone leptin, which may impede successful fertilisation.

Obesity reduces the chances of successful IVF

Australian researchers found that, compared to obese women, those with a BMI between 20 and 24.9kg/m2 had a 60% greater chance of a successful assisted reproduction treatment. The scientists speculated that this reduced fecundity may be due to disturbed endometrial function — in other words, the uterus of obese women appears less capable of receiving the embryo after the transfer.

Other studies suggest that overweight and obese women have a lower response rate to fertility drugs. It seems that high levels of body fat impede the proper absorption of the fertility drugs used during treatment.

Polycystic Ovarian Syndrome (PCOS)

Women with PCOS often have trouble conceiving. This endocrine condition is characterised by insulin resistance, which causes the ovaries to produce an excessive amount of testosterone. As explained earlier excessive testosterone inhibits ovulation, making it harder for the women to conceive. People with insulin resistance are also more prone to weight gain.

Improve your chances of conceiving

According to the American Society for Reproductive Medicine, reducing body weight by only 5-10% can considerably improve ovulation and pregnancy rates.

Losing it: Making weight loss easier

Be realistic

If you have some excess weight to shed, remember that these extra kilos didn’t appear overnight. So be patient and don’t fall for the fad diet du jour as trying to lose weight fast can wreck havoc on your body and your hormones would go haywire. In fact, crash dieting would be like playing Russian roulette with your reproductive system; research has even linked extreme diets to infertility among young women. Aim to lose not more than 4kg per month.

Exercise and eat healthy

Everyone knows that exercising regularly and adopting healthy eating habits can help drop excess kilos. So, here’s an incentive: a US study involving 439 overweight-to-obese, sedentary women showed that participants who improved their diets and exercised regularly lost almost 11% of their original weight (an average of about 10kg). On the other hand, those who changed their diets only but remained sedentary lost 8.5% of their starting weight while those who exercised but did not improve their eating habits shed 2.4% of their weight.

Exercise tips:

  • Start slowly (even if it’s only 10 minutes per day) and gradually increase to 30-45 minutes a day.
  • There’s no need to be an athlete or hit the gym everyday; walking, biking, swimming or your favourite sports count as well.
  • Try a mix of aerobics and cardiovascular exercises for better results.

Diet tips:

  • Don’t skip your main meals, especially breakfast. This will help prevent overeating at the next meal.
  • Have 500ml of water at least 30 minutes prior to your meal — studies suggest that this could help reduce your overall calorie intake.
  • Keep your portion size in check; use the Eatwell guide as a guide. Make sure to always include a lean protein source (beef, chicken, fish, legumes or pulses) and lots of vegetables (especially green leafy ones) at every meal. Protein and fibre exert great satiety effects — this can help you reduce your food intake without much effort.
  • Try to eliminate refined products (like white bread, white pasta and products made from white flour) and sugary foods from your diet. These foods are rapidly digested causing a surge in blood glucose levels. This in turn causes a spike in insulin levels promoting accumulation of body fat. The same goes for soft drinks and fruit juices.

Keep a food journal

Recording what you eat and drink throughout the day can help you spot ‘sneaky’ foods and beverages that are high in calories and may be thwarting your weight loss efforts.

Drink up!

We often mistake hunger as thirst so when you feel hungry, down a tall glass of water first and wait a bit before eating.

Eat home-made food

Prepare your food yourself — doing so will give you more control over what and how much you eat.


    Bates GW (2013) Prevention of Infertility Source Document. Abnormal body weight: A preventable cause of infertility (Accessed August 2013).

    Mason et al (2013) History of weight cycling does not impede future weight loss or metabolic improvements in postmenopausal women. Metabolism. 62(1):127-36.

    Gesink Law DC, Maclehose RF and Longnecker MP (2007) Obesity and time to pregnancy. Hum Reprod. 22(2):414-420.

    Pigny et al (2000) Serum levels of inhibins are differentially altered in patients with polycystic ovary syndrome: effects of being overweight and relevance to hyperandrogenism. Fertil Steril. 73(5):972-977.

    Wang JX, Davies M, Norman RJ (2000) Body mass and probability of pregnancy during assisted reproduction treatment: Retrospective study. BMJ. 321(7272):1320-1321.