How can we improve the chances of pregnancy for women who are obese? 0

The extent of the issue

Obesity is a public health issue both in the general population and in women of childbearing age. Far from improving, the problem has progressively increased over the last few years.

A study published in the journal The Lancet concludes that 13% of the world population has weight issues. In Spain, there is a growing trend in the number of people suffering from this illness which is particularly alarming as it positions Spain as the second European country, after the United Kingdom, with the largest number of cases of obesity and excess weight.

The prevalence of obesity is high in the USA and Europe and it is increasing in practically all countries. In the USA, over 36.5% of adults are obese; obesity (BMI: Body Mass Index ≥ 30 kg/m2) during a woman’s childbearing age affects 31.8% of women between 20 and 39 years of age and this figure increases to 58.5% when excess weight and obesity are combined.

The impact of obesity on fertility

Fertility issues in obese women (BMI ≥ 30) are, in most cases, linked to ovulatory dysfunction and, in some cases, to polycystic ovary syndrome. Furthermore, it should be highlighted that in women with normal ovulatory cycles, obesity itself is linked to a lower spontaneous pregnancy rate and an increase in the time taken to get pregnant. A recent study found that obese women who are in the latter stage of their reproductive years (35 to 49 years of age) have significantly lower levels of AMH (anti-Müllerian hormone, a hormone that provides information on ovarian reserve). That is, up to 65% compared with women of the same age and normal weight.

What this tells is that obese women will have more issues getting pregnant naturally, will take longer to do so and also have less real time in which to achieve it, even if they have apparently normal cycles, because they appear to have a lower ovarian reserve. Numerous studies prove that a 5 to 10% weight loss leads to a notable improvement in their prognosis.

Assisted reproduction treatment (ART) in obese women

The data suggests that, as a woman’s BMI increases, there is an increased failure rate following ART (IVF: in vitro fertilisationICSI: intracytoplasmic sperm injection) and it has been linked to a decrease in the quality of the oocytes obtained, poorer ovarian response, poorer endometrial quality and endometrial receptivity or a combination of all these factors.

A meta-analysis analysing 48,000 cycles of IVF/ICSI confirms a lower clinical pregnancy and live newborn infant rate and a higher spontaneous pregnancy loss rate in women with a BMI > 25 kg/m2 in comparison with women who have a normal BMI. An increase in the prevalence of other types of complications, such as ectopic pregnancies, ovarian hyperstimulation syndrome and so on, has not been demonstrated.

A recent study (2017) looks into the impact of obesity on fertility in obese women. Obesity would be appear to affect the oocyte and embryo pre-implantation, amongst many other factors that are being analysed. This might explain subfertility, which is caused by abnormal receptivity and which can lead to abnormalities in the placenta that manifest themselves in increased cases of spontaneous pregnancy loss, foetal death and preeclampsia amongst the obese.


Several observational studies have found that a 5 to 10% weight loss in obese women with fertility issues improves ovulation frequency and the chances of getting pregnant.  Women with obesity (BMI ≥ 30 kg/m2) should speak to a team of experts so that their cases can be assessed.

Alicia López, nutritionist and dietician at Instituto Bernabeu

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