Overweight and obesity are increasingly prevalent in developed countries and are linked to many health problems. In recent decades, obesity has become a global pandemic.

The origin of obesity is multifactorial, resulting from the interaction of multiple elements, including genetic, metabolic, environmental, cultural and socio-economic factors.

The body mass index (BMI) is considered in clinical practice as the most widely accepted population-based measure for estimating the degree of obesity. It is calculated as the ratio of weight (kilograms) to the square height (metres). It is considered overweight when the BMI is between 25 and 29.9 and obesity when the BMI is equal to or greater than 30.

Fertility is not outside this problem, which is why many overweight women and couples seek help when faced with the difficulty of having children, as obesity is a direct cause of numerous disorders that can negatively affect the chances of achieving a pregnancy.

Obesity And The Likelihood Of Pregnancy

Obese women are two to three times less likely to get pregnant naturally. This can be explained by ovulation problems (the woman does not ovulate or the ovulation is not of good quality), which also translates into possible problems with the embryo.

In addition to ovulation, obesity also affects the endometrial layer of the uterus, which is the most important area for proper embryo implantation.

Obesity And Endocrine Changes

The most important endocrine change caused by obesity is the elevation of basal insulin levels and insulin resistance, which leads to alterations in menstrual cycles and ovulation.

On the other hand, oestrogen -which is the sex hormone produced in women mainly in reproductive organs- is also produced in fat and fatty tissues. Because of this, women with obesity will have higher levels of this hormone, triggering an imbalance of the hormonal axis due to an excess of oestrogen.

Polycystic Ovary Syndrome And Its Relationship To Obesity

Polycystic ovary syndrome (PCOS) affects between 12% and 21% of women of reproductive age and is the most common cause of anovulation and therefore infertility.

Typically (but not exclusively) patients with PCOS are overweight and have irregular menstrual cycles.

The Rotterdam criteria are used for the diagnosis of PCOS, which require at least two of the following features: oligo- or anovulation; clinical and/or biochemical manifestations of hyperandrogenism (such as acne and hirsutism) and ultrasound-described polycystic ovarian pattern.

PCOS symptoms may improve with a weight loss of 5% to 10%.

How Obesity Affects Assisted Reproductive Treatments

Both artificial insemination and IVF are affected by obesity and are associated with a decreased chance of success in these treatments.

In assisted reproduction processes, obese women require higher doses of gonadotrophins due to greater resistance to them, causing a worse ovarian response. The dose of gonadotropins needs to be increased as the patient’s weight increases, which leads to longer and more costly treatments due to a greater use of medication.

It is also associated with a higher incidence of miscarriage and problems during pregnancy, delivery and postpartum.

During pregnancy, obesity increases the likelihood of developing gestational diabetes, high blood pressure, preeclampsia and cesarean delivery, among other complications.

There are also studies that link children born to obese mothers with a higher risk of developing later problems such as cardiovascular disease, metabolic syndrome, type II diabetes and obesity.

healthy lifestyle together with good eating habits will increase the probability of success both in achieving a pregnancy naturally and with the help of assisted reproduction techniques.

Obesity And Fertility: Not Only A Female Problem

The male partner does matter a lot in the field of assisted reproduction, as he, together with the female partner, determines the success of the results.

When we talk about overweight, problems have also been described in the number and mobility of sperm in obese men (there are studies that show that the concentration of sperm in the semen of obese men is between 10 and 20% lower than that of normal-weight men). In addition, obesity in men is also associated with hormonal alterations, such as a drop in testosterone levels and other important hormones in the field of reproduction.

As in women, a correct diet together with healthy lifestyle habits will help to improve seminal quality.

All this makes it necessary to correct problems of overweight and obesity in the couple with gestational desire before trying for a baby, whether it is sought naturally or with the help of assisted reproduction techniques.

A hypocaloric diet and physical exercise, in combination with adequate psychological support and within a multidisciplinary framework, is the first option to be advised for all obese patients who wish to achieve pregnancy.

Dr. Ana Gallardo Carvajal
Gynaecologist specialising in reproductive medicine

URE Gutenberg Centre

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