All About Fertility

Sterility and Infertility - "Weight and Infertility"

Body weight has important implications on the chances of a couple reproducing. A drastic change in normal body weight, whether weight gain or weight loss, can cause infertility in both men and women, and can even lower the chances of success of assisted reproduction treatments. It has even been suggested that as much as 12% of primary infertility is a consequence of weight problems.

Body fat affects the production of Gonadotropin-releasing hormone (GnRH) which is essential both for regular ovulation in women and for sperm production in men. Specifically, GnRH activates the secretion of Luteinizing hormone (LH) and of Follicle-stimulating hormone (FSH), both of which are vital for the development of ova and spermatozoa.

weigth and infertility

What is the Body Mass Index?

For discussing ideal weight, obesity or low weight, we normally talk about Body Mass Index (BMI). Body Mass Index (BMI) is a measure of the relationship between an individual’s weight and their height. It is calculated using a simple mathematical formula: weight (in kilograms) divided by height (in metres) squared. A BMI between 18 and 25 is considered an ideal or normal relationship between weight and height.


A.) In women: a great number of common disorders are related to obesity in women, which can have a negative effect both on getting pregnant (either naturally or with the help of assisted reproduction techniques) and on carrying a pregnancy to full term. Some of the main problems relating to obesity which affect fertility are:

Due to high levels of insulin in the blood, the ovaries release too many androgen hormones, and this can cause excessive growth of facial hair, weight gain and infertility. Women who suffer from PCOS have a greater risk of developing diabetes and of suffering from cardiac diseases.

Losing weight can be very beneficial for curing this disorder or condition in part, however it may not be necessary to lose a significant amount of weight. Losing just 5% of their body weight could be beneficial for helping women to become pregnant.

  • Polycystic Ovarian Syndrome: Polycystic Ovarian Syndrome (PCOS) is one of the biggest causes of anovulation, and, as a result, of sterility. In order for PCOS to be diagnosed precisely, women must present at least two of the following symptoms:
    • Irregular menstruation
    • Enlarged ovaries, with many small follicles, identified by ultrasound
    • An excess of androgen hormones
  • Hypothyroidism: hypothyroidism is a type of disorder of the thyroid, and it is characterised by abnormal production of hormones in the thyroid gland. This condition commonly causes people to gain weight and afterwards it is very difficult for them to lose the weight gained in the past. It also causes periods to be irregular and can sometimes interrupt ovulation or even stop it altogether.
  • Luteal phase defects: luteal phase defects are part of a series of hormonal changes relating to the adequate development of the endometrium, which is vital for embryo implantation and consequently for achieving a full-term pregnancy. During the second half of a woman’s menstrual cycle, the corpus luteum is responsible for producing progesterone in order to thicken the endometrium. If the luteal phase is too long, or if on the other hand it is not long enough, progesterone levels will not be adequate, giving rise to abnormal menstruation.
    When a woman is pregnant, luteal phase defects can cause spontaneous miscarriage.
  • An excess of oestrogen: oestrogens are sex hormones produced in women’s bodies, mainly by the reproductive organs, but also elsewhere in the body, including in lipocytes, or fat cells. Given that oestrogen is produced by fat-storing cells, women who are obese or overweight – in general – have larger quantities of oestrogens in their system than women who are a normal weight. At normal levels, oestrogens play a fundamental role in many organic functions. However, when there is an excess of oestrogens in the system, these can attack the woman’s reproductive system and lead to an imbalance, causing infertility. Even in cases where women become pregnant, excess oestrogen can increase their chances of having a spontaneous miscarriage. On the other hand, it must be taken into consideration that weight is not the only factor that can bring about an increase in oestrogen levels.

B.) In men: excess body weight can cause a lower sperm count or lead to lower sperm activity. In fact, excessive weight can reduce the sperm count and the concentration of spermatozoa in a semen sample by approximately 21.6%, and in cases of morbid obesity this rises to 23.9%.

Being Underweight

A.) In women: drastic weight loss or illnesses such as anorexia nervosa can have an effect on a woman’s fertility.

GnRH production can also be reduced as a consequence of low body weight in women. As a result, ovulation can become irregular and can even stop. Decreased levels of GnRH can also affect the availability of the uterine lining for enabling an embryo to become implanted.

Too much exercise can also alter the balance of hormones and cause a decrease in fertility.

B.) In men: having a low body weight can cause an even more severe reduction than obesity in terms of a man’s sperm count and sperm activity. In fact, being underweight can reduce the sperm count and the concentration of spermatozoa in a semen sample by approximately 28.1%, and for those who are severely undernourished it can be reduced by as much as 36.4%.

What can you do?

Returning – healthily – to a normal weight is often enough to remedy hormonal imbalances, and this normalisation enables fertility to be restored. In addition, weight loss by obese individuals increases their chances of a successful pregnancy.

Alternatively, medications can be used to increase fertility, though this process is always controlled by a doctor. However maintaining a healthy weight is the best treatment.

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