Effects of Obesity on Fertility Research

Effects of Obesity on Fertility Research

According to the WHO latest data, more than 1.9 billion adults over 18 are overweight, while more than 600 million people around the world already progressed to some form of obesity. When it comes to obesity, there are probably no people who have never heard of that being overweight is associated with a higher risk of cardiovascular diseases, diabetes, disorders of the musculoskeletal system, as well as the emergence of many other serious health problems. But what many may not know is that overweight significantly reduces the chances of conceiving a child, and further in this paper, we explore a variety of direct effects obesity produces on fertility in both women and men. Effects of Obesity on Fertility Research


Obesity and reproductive system

According to Sharma et al. (66), up to 15% of world population may be impacted by infertility today, as the key factor causing the increase in this indicator is seen in the lifestyle factors, mainly eating disorders and hypodynamism. Indeed, as Martini et al. (139) mark, since obesity and infertility have been showing growth in parallel during the last decades, the appearance of a hypothesis on their co-dependence seems to be grounded enough.

Thus, as studies show, when body mass index moves from the “overweight” level (BMI of 25-29.9) to “obese” (BMI of 30 and above), drastic hormonal changes start being observed. For instance, obesity in women is characterized by either hyperandrogenism or increased secretion of estrogen, both of which lead to the reduced frequency of spontaneous pregnancies occurrence (Sharma et al. 68). Moreover, according to Southall (26), these mechanisms are formed back in adolescence. In obese adolescents, menstruation onset takes place significantly later or earlier it normally should, and when the active reproductive age is reached, abnormal metabolic processes lead to other menstrual function disorders like irregular cycles, hypomenstrual syndrome, and even cessation of menstruation (Southall 27).

Besides, obesity is often associated with polycystic ovary syndrome (Stern 763). At PCOS, one of the major pathogenetic mechanisms is insulin resistance (Nelson 23). As Nelson (24) explains, being the main risk factor on the way to diabetes, developing insulin resistance also provokes abnormal menstrual cycles and leads to anovulation, a condition where the organism does not produce a mature egg. It is believed that hyperinsulinemia response violates normal folliculogenesis, and the recovery of ovulation observed in women with PCOS due to body weight loss and metformin treatment (Nelson 25), supports this idea. Effects of Obesity on Fertility Research

However, even in the absence of PCOS, obese women have fertility problems. For instance, time to pregnancy is known to increase proportionally to the increase in body weight, since the adverse factors associated with obesity damage ovarian function and reduce the overall quality of oocytes, as well as negatively affect the receptor apparatus of the endometrium (Stern 764-5). As a result, according to Sharma et al. (68), women with BMI over 30 have longer time to pregnancy than women with BMI between 20 and 25, and a significantly lower miscarriage rate (10.7% in normal BMI to 13.6% in obese women).

Moreover, obesity complicates pregnancy regardless of whether partners practice a natural method of conception or resort to reproductive technologies such as in vitro fertilization. Specifically, obese women have higher risk of failure in the treatment of infertility using assisted reproductive technologies compared to women with normal body weight. Several studies have demonstrated that reduced effectiveness of infertility treatment was associated with a lower quality and quantity of oocytes obtained as well as low quality of embryos (Stern 765). Other studies have shown that under comparable indicators of frequency of clinical pregnancy and live births, women with obesity require higher doses of gonadotropins to stimulate ovulation compared with women with normal body weight (Nelson 25). Overall, a systematic review and meta-analysis of studies that included nearly 48 thousand of IVF treatment cycles using own oocytes reveals that women with the BMI ≥25 kg/m2 compared to women with the BMI <25 kg/m2 show small but statistically significant decrease in the frequency of clinical pregnancy (RR = 0.90) and live births (RR = 0.84), and a significant increase in the risk of early pregnancy loss (RR = 1.31) (Stern 766). According to Nelson (25), the risk of miscarriage can be caused by both hormonal disorders noted above and the poor quality of the egg, which the ovaries produce.

However, while the connection between obesity and infertility in women had long been known, studied and proven, the male obesity was noticed much later. Meanwhile, obesity in men is often a key issue in childless couples. Thus, it is well established that obesity in men results in much less normal sperm cells than in men of average weight. In particular, the higher BMI becomes, the more there are defects in composition and characteristics of sperm, such as the total number of sperm cells, the number of progressively motile sperm cells, viscosity and liquefaction of the ejaculate (Martini et al. 142). In addition, men with the BMI of less than 25 generally have larger volumes of ejaculation (Martini et al. 143). In some cases, there is also a connection of high percentage of body fat with an amount with impaired protein providing sperm quality and functionality (Martini et al. 143).

Obesity in men also leads to a decrease in testosterone levels, which is directly linked with infertility. As Martini et al. (144) report, some studies demonstrate that the possible mechanisms beyond the negative impact of excessive BMI on testosterone levels are the reduced pituitary and hypothalamic secretory function, reduced circulating sex-hormone binding globulin and excess estrogen production found in obese men. In addition, obese men are more likely to develop erectile dysfunction – another key reason for the decline in male fertility. In general, irrespective of the differences in location and methods applied, various international studies reveal a higher prevalence of erectile dysfunction in obese males in comparison to men with normal BMI (Sharma et al. 68). Meanwhile, as Sharma et al. (69) cite Corona et al., 96.5% out of 236 men with metabolic syndrome report erectile dysfunction and nearly 40% struggle with reduced libido and hypoactive sexual desire.


Although it is not fully known now, which of these factors (or their combination) is the major cause of infertility in obese men and women, it is clearly understood that obesity has a negative effect on their reproductive system, while weight reduction shows to result in the restoration of fertility.Effects of Obesity on Fertility Research

Conclusion and Recommendations

Obesity is an endocrine disease, but it is based on the violation of the balance of energy consumption and expenditure, as well as qualitative hunger, i.e. insufficient intake of micronutrients required for normal metabolism. Therefore, metabolic disorders in obesity inevitably involve the endocrine and reproduction systems in the pathological process. Thus, in men, obesity is associated with hypoandrogenaemia and hypogonadism. In contrast, women with obesity are characterized by hyperandrogenemia as a result of male type obesity or increased secretion of estrogen in case of female type obesity. Moreover, women with obesity compared to women with normal body weight have decreased occurrence frequency of spontaneous pregnancies and the effectiveness of infertility treatment by various methods (ovulation stimulation, ART).

A number of studies demonstrate that weight loss has a positive effect on menstrual function, increases the likelihood of conception and birth of a healthy child, reduces the risk of adverse pregnancy outcomes in women, as well as decreases the hormonal imbalance and restores the quality of sperm in men. Thus, working on one’s weight and taking the path of a healthy lifestyle that includes regular exercise, reducing portion sizes and a choice of healthy foods can significantly reverse the destructive processes and restore reproductive function.Effects of Obesity on Fertility Research