Effects of Obesity on Fertility and Pregnancy

Obesity is becoming a common problem in women of reproductive age. According to the definition by the World Health Organization (WHO), the body mass index of 25 and above (BMI = weight in kilograms divided by squared height in meters) characterizes a person as overweight. BMI of 30 or above defines obesity, 35-40 corresponds to severe obesity and above 40 is extreme obesity.

The WHO reports that in most European countries and the United States up to 60% of women are at least overweight, 30% are obese and 6% could be severely obese.

Infertility in couples is defined as failure to conceive naturally after 12 months of unprotected intercourse and is becoming a rising problem today, affecting at least 1 in 8 couples. Sperm problems, disorders of ovulation, advanced reproductive age in women, anatomical problems such as obstructed fallopian tubes and endometriosis are known causes, while in 10% of cases the infertility remains unexplained.

There are many consequences of obesity which affect general health:

• Insulin resistance and diabetes
• Hyperlipidaemia and cardiovascular disease
• Sleep apnea and respiratory problems
• Osteoarthritis

There is much evidence that obesity has also a negative impact on fertility in both sexes, and this becomes worse with increasing BMI. Obesity has also negative impact on the course and outcome of pregnancy.

It is well known for decades that obese women with polycystic ovaries and higher levels of androgens have irregular periods and difficulties to conceive because of lack of ovulation.

Many population studies have confirmed that obesity is linked to delay in natural conception and this becomes worse with increased BMI.

It is also documented that the effectiveness of fertility treatments is reduced with the degree of obesity. Women with increased body weight do not respond well to clomiphen citrate induction of ovulation and also require larger doses of gonadotrophin injections to achieve ovarian stimulation for in vitro fertilization (IVF).  Many studies have also indicated that the success rates of IVF are becoming lower the higher the BMI is.

Obesity affects the course of pregnancy, after natural or assisted conception. There is evidence that severe obesity is related to early miscarriage or even recurrent miscarriages and the aetiology is not very clear. Obese pregnant women have higher risk to develop gestational diabetes, hypertension and preeclampsia. These conditions would lead to more premature deliveries, more caesarean sections and more maternal and fetal risks and complications.

It seems that obesity is a severe metabolic derangement which affects many body systems. The excess adipose tissue acts as endocrine organ that produces many hormonal substances such as leptin, adiponectin, resistin, cytokines, that affect metabolism, neuroendocrine functions and induce a chronic inflammation status.

The most well known mechanism is that obesity promotes insulin resistance, increases the levels of insulin and androgens and causes disturbance of ovulation, especially in women with significant abdominal obesity. The obesity related decrease in reproductive performance exists also in obese women without insulin resistance and ovulation disorders. This fact indicates that obesity also affects fertility in various other levels: These can be the secretion of gonadotrophins from the pituitary, the maturation and quality of oocytes and the receptivity of the endometrium which can be influenced negatively by the above mentioned endocrine and inflammatory factors.

It is a difficult task to treat obesity, and the options are diet, lifestyle changes and regular exercise, or even bariatric surgery in extreme cases. It should be noted that reduction of body weight improves significantly the chances of conception and the success rates in IVF. All obese patients with infertility should be encouraged to a quick weight loss before entering IVF treatment, especially those with BMI above 35. Even a 5-10% reduction in body weight results in increased conception rates and reduction of pregnancy complications.