Are you too heavy to get pregnant? The role of weight in infertility in women and couples

A 2015 figure from the American Society for Reproductive Medicine shows that obesity affects about 50% of the infertile population in the world; this finding suggests that there may be a clear correlation between weight gain and reduced fertility in the general population.

Overweight and obesity are one of the major public health problems of our times. According to the WHO, they could come to replace more traditional problems such as malnutrition and infectious diseases.

Obesity is defined as an excessive accumulation of fat tissue compared to lean body mass. In particular, a measure to define the balance between fat mass and lean mass in the human body is given by the measurement of the Body Mass Index , known as BMI¹: a BMI greater than 25 kg/m2 represents an overweight condition , while if the BMI is higher than 30 kg/m2 we speak of obesity .

Obesity in 2004 is defined by WHO experts as a global epidemic. In 2014, the prevalence of obesity was 600 million people worldwide and today this value is constantly increasing.

The link between obesity and infertility

Obesity is currently considered one of the main health challenges of our millennium: in the vast majority of cases, voluptuary habits, psychogenic causes, inadequate or insufficient physical activity or family aggregation phenomena are responsible for it, only rarely is obesity the consequence of a pathological condition on a genetic or endocrine basis.

A 2015 figure from the American Society for Reproductive Medicine shows that obesity affects about 50% of the infertile population in the world ; this finding suggests that there may be a clear correlation between weight gain and reduced fertility in the general population.

Infertility is defined as the inability of a couple to achieve pregnancy after at least 12 months of regular unprotected intercourse. This condition affects about 15% of couples.

The link between obesity and infertility has been extensively studied and it is now clear that as the BMI increases, the woman’s risk of developing fertility problems also increases. In particular, overweight and obesity are responsible for the appearance of irregular cycles, up to frankly anovulatory pictures, have a negative impact on the development and quality of oocytes and embryos and have a direct negative effect on endometrial receptivity, thus increasing the risk of failed intrauterine implantation of the embryo and first trimester miscarriage.

Many studies in the literature demonstrate that in obese women there is an alteration of the gene expression of the endometrial receptors precisely during the implantation window, i.e. in the days in which there should be a direct dialogue between the mother’s uterus and the embryo. This phenomenon unfortunately involves the alteration of those signals which should allow the mother’s uterus and her embryo to speak and understand each other, with a consequent reduction in the possibility of pregnancy onset and an increased risk of miscarriage.

Obesity is also a disease closely linked to the development of insulin resistance , a clinical condition underlying the onset of diabetes but also typical of situations at risk of chronic anovulation such as micropolycystic ovary syndrome : the presence of an insulin resistance mediated by excess adipose tissue has a negative impact on the production of ovarian hormones, estrogen and progesterone, with consequent alteration of the functionality of the ovaries themselves and progressive disappearance of ovulation phenomena.

Obese women have a 4 times increased risk compared to normal weight women of not ovulating , i.e. of not producing the egg cell adequately, and this risk is all the more serious the earlier the onset of obesity (childhood obesity) is.

Fat cells also produce a hormone, leptin , which worsens this mechanism. Therefore insulin resistance and impairment of ovarian function are proportional to the severity of obesity.

The disposition of body fat also plays an important role, in particular the phenomena described up to now are more evident in the presence of central obesity, i.e. an accumulation of “apple-shaped” body fat, i.e. at the abdominal level.

Micropolycystic ovarian syndrome (PCOs) is one of the main causes of female infertility and affects about 10% of women of childbearing age. Often the woman affected by PCOs is overweight or even obese, and presents an apple-shaped obesity. This condition, which also recognizes a genetic predisposition, is frequently associated with chronic anovulation.

But obesity not only plays an important role in the natural fertility of couples, it also has a negative impact on the outcome of Medically Assisted Reproduction treatments.

Obesity and success of assisted reproduction treatments

First of all, in an obese woman subjected to hormonal stimulation for PMA, it is necessary to use a higher dosage of drugs than in a normal weight patient in order to obtain an adequate response to the proposed therapy. The use of higher drug dosages and for a longer time is due to the fact that in these patients the drug seems to have less efficacy. However, despite these precautions, the number and quality of oocytes recovered in these patients is lower than in patients of normal weight : the oocytes of obese patients, damaged by oxidative stress phenomena, are genetically more fragile and therefore give rise to poor quality embryos that find it difficult to implant themselves in the uterus and give rise to a pregnancy.

Furthermore, the alteration of endometrial receptivity, typical of these women, leads to an increased risk of miscarriage and a drop in implantation rates even after IVF/ICSI.

Finally, it should not be forgotten that an obese patient undergoing IVF/ICSI has an increased risk of experiencing complications during the treatment : injuries during the oocyte retrieval operation, abnormal bleeding, difficulty in recovering the oocytes.

But obesity and its impact on fertility are not just a female problem, in fact it has been amply demonstrated that men too suffer a reduction in fertility proportional to the pathological increase in body weight.

The role of obesity in male infertility

The mechanisms underlying this condition are mainly due to the excessive production of estrogen by excess adipose tissue, with consequent alteration of the control mechanisms of the hypothalamic-pituitary hormonal axis, and negative influence on sperm production . Often in obese males there may be an increase in intratesticular temperature due to poor movement and prolonged sitting. Finally, as for women, there is also evidence for men that demonstrates how obesity also has a negative impact on the outcome of Medically Assisted Procreation treatments , as a consequence of the reduced concentration and motility of sperm.

Considering what we have said so far, we can conclude that obesity can be considered a cause of infertility.

The comforting fact is that it is a reversible condition, as the damage to reproductive capacity due to obesity regresses in the presence of an adequate weight loss.

How to lose weight?

It is extremely important to carry out appropriate counseling with infertile couples, in which one or both partners are affected by obesity, regarding the importance of undergoing an adequate diet and undertaking a course of physical activity aimed at losing weight and consequent restoration of reproductive capacity.

There is clear evidence that weight loss increases spontaneous ovulation phenomena in women with anovulatory cycles, improves insulin resistance and reduces the incidence of genetic damage from oxidative stress. In men, on the other hand, weight loss improves sperm quality and reduces sperm DNA fragmentation (i.e. damage to the cell nucleus), thus improving egg fertilization rates.

Weight loss can be achieved with diet or physical exercise, but the ideal would be to combine the two in order to reduce time and optimize results: among the physical activities, aerobic sport is preferable (running, brisk walking, Nordic walking, tennis, swimming) versus isometric and concentric work sports (such as weight training). Physical activity not only plays an important role in improving insulin resistance, but also has an effect on oxidative stress which significantly damages the functionality of oocytes and sperm, inducing the formation of embryos that are unlikely to implant in the mother’s uterus and they will give birth to pregnancies.

To optimize times and if necessary, specific drugs, recently approved by the FDA, can be added to diet and physical exercise and should be administered for a period of at least 6-12 months (Orlistat, Sibutramine as well as some antidepressants): it should be specified that these substances are absolutely contraindicated during pregnancy and therefore, during their use it is advisable to associate contraceptive methods.

What weight to achieve before trying to get pregnant?

Weight reduction is always effective, however there are no precise guidelines on what is the ideal body weight for an obese patient to reach before directing him to seek pregnancy or embark on a path of ART.  There is evidence that would demonstrate that a weight loss equal to 3-5% of body weight can already lead to a marked improvement in fertility.

Clinical practice suggests that it is preferable to obtain a BMI of less than 30 kg/m2.

The fact that the importance of restoring an adequate body weight also has a direct impact on the patient’s self-esteem and therefore on his social life and sexual activity should not be underestimated, which also determines further success in terms of improving fertility .

An important fact to underline is that, if it is true that excessive body weight negatively affects fertility and the outcome of MAP treatments, the opposite is absolutely not true: i.e. MAP treatments aimed at seeking pregnancy have no impact on changes in body weight.