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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.

When are women mostly fertile?

Fertility is a combination of many factors.  For women, it varies during their menstrual cycle as they cannot get all days during their cycle. Women’s fertility greatly varies during their lives.  In addition, women of the same age have different chances of getting pregnant, due to different lifestyles and general health.

During the menstrual cycle there is the so called “fertile window” during which women can get pregnant.  Ovulation is the time that the oocyte is released from the follicle and can be fertilized by the sperm for about 24 hours. The sperm may be possible to fertilize the oocyte for about three days depending on the sperm quality. As a result, having regular intercourse at the time of ovulation and a few days before ovulation is the optimal time to achieve a pregnancy.

Women are born with a finite number of oocytes. Every month a number of oocytes becomes atretic and can no longer be used.  Oocytes of better quality are first used during a woman’s life. As a result, the number of oocytes is reduced with age, oocyte quality deteriorates and the chance of getting pregnant decreases. The chance of having a miscarriage also increases with age because of increased number of chromosomal anomalies in oocytes of older women.

Age is the most important factor related to a woman’s fertility and her chance of getting pregnant.  It is a fact that the chances of getting pregnant decreases with age although the exact time when it starts to happen may vary.  In general, women younger than 35 years of age have better chances of conceiving a child. Women during the third decade of their lives have even higher chances. Women younger than thirty have about 20%chances of getting pregnant every month. This is reduced to 5% by the age of 40. A fact not only for natural conception but also for assisted reproduction treatments.

However, women of all ages, even younger women, may improve their conception potential by improving their lifestyle.

Quitting smoking that affects oocyte quality but also harms the embryo during pregnancy is an important step.

Reducing caffeine and alcohol consumption may assist.

Improving diet (Mediterranean diet is an excellent example of a healthy diet) and having a BMI within normal range maximizes the chances of getting pregnant.

Obesity is related to reduced fertility and increased pregnancy complications.

Hormones play a key role in reproduction and a  normal thyroid function and optimal vitD levels improve the chances of getting pregnant and reduce miscarriage rates.