There has been an increase in the prevalence of obesity worldwide. According to World Health Organisation (WHO), the worldwide prevalence of obesity has almost doubled in the last three decades.
Obesity is defined as body mass index (BMI) of more than 30kg/M2. We know that women with a BMI over 30kg/M2 are three times more likely to suffer from infertility.
In the UK, we do not collect data on the prevalence of obesity in women in the reproductive age group (between 19 to 50 years of age). So, it is difficult to know the exact prevalence of overweight and obesity in women in the reproductive age group.
Someone gets the label obese if their BMI is over 30kg/M2. With a BMI of over 25kg/M2 someone is by definition overweight. Given these measures, it is important to understand how obesity can affect female fertility.
Can it affect ovulation?
Women with BMI of over 27kg/M2 are three times more likely to experience irregular or infrequent ovulation. The fatty tissue (technically adipose tissue) disturbs the female hormone system. This happens through special chemicals such as leptins, insulin and adipokinins. These chemicals create a hormonal imbalance both in the ovary and in the regulatory system in the brain.
The changed hormonal environment prevents proper development of the follicle and ovulation each month. This leads to absent or infrequent ovulation. It also reduces your chances of conceiving each month. These effects are seen in obese women with or without polycystic ovarian syndrome (PCOS).
When thinking of fertility, even a loss of 5% of the current weight can regulate your ovulation and period. Patients with BMI of more than 30kg/M2 will not be eligible for the NHS funding of the fertility treatments. Most private fertility clinics will treat patients with BMI of less than 35kg/M2.
Can obesity affect the womb lining?
As we know, the implantation rate of the embryos following an IVF or ICSI treatment drops with increasing BMI over 30kg/M2. It is not exactly understood how BMI affects the womb lining or endometrium. Scientists think that the fatty tissue converts the high circulating amounts of steroid hormone into oestrogen.
The result is higher circulating levels of oestrogen. Together with high levels of other hormones such as Insulin, the potential of the womb lining to receive the embryo is affected. The womb becomes less receptive and favourable for embryo implantation and an ongoing pregnancy.
Does obesity affect the egg maturity and quality?
Important to note is that high BMI not only affects regular ovulation. It also influences the quality and the maturity of the released egg. This effect is seen in natural ovulation and with fertility treatments. There is a lack of clear understanding. Scientists think that this results from a hormonal imbalance in the ovaries.
Does higher BMI affect the chance of my fertility treatment working?
As mentioned earlier, it can affect your response to the ovulation Induction fertility drugs. These are clomiphene (Clomid®) or gonadotropin injections. It may lead to a higher cancellation rate of the ovulation induction treatment cycles. If you are going through an IVF or ICSI treatment, you will start on a higher dose of the stimulation drugs (Menopur®, Gonal F®, Fostimon®, etc.). Also, you may need a much higher total dose of the stimulation drugs. Despite the use of higher fertility drug doses, it may result in the development of fewer follicles.
At egg collection, we observe lower numbers of mature eggs. When inseminating the eggs with sperms, the fertilisation rates are almost 5-15% lower than with women who have a BMI of less than 25kg/M2. In view of these effects on egg quality, it also affects the quality of the embryos. If it does, then these embryos will be less capable of implanting and resulting in an ongoing pregnancy. This results in the rise in early pregnancy loss or miscarriage.
If you are overweight or obese, we recommend managing your weight before starting fertility treatment. This will help you in improving your fertility treatment (IVF, ICSI or Ovulation induction) success rate.