The science of getting pregnant and having healthy babies is such a complex process that those who get pregnant and bear live healthy babies with ease are indeed lucky. Being in good health, with balanced and synchronised hormones, minerals and vitamins, organs, and systems is essential to achieving pregnancy, carrying the pregnancy to term and giving birth to live and healthy babies.

Getting pregnant is not so easy, even for couples who have normal physiological parameters. For example, a couple who have no medical abnormalities, including healthy weight with a body mass index (BMI of 19-25kg/m2), have only an eighty per cent chance of getting pregnant within one year of having unprotected sex. It gives an insight into how even being overweight or obese can decrease your chances of getting pregnant or carrying a pregnancy safely for nine months without complications. In this article, we will discuss the effect of obesity upon fundamental reproductive mechanisms and its relation to fertility treatments.

Obese women experience impaired fertility in both natural and assisted conception cycles. The mechanism through which obesity affects fertility is, however, controversial—obesity characterised by excess fat storage. Definitions of obesity can vary, but the most widely accepted definition is that of the World Health Organisation’s body mass index [BMI (kg/m2)] criteria. A person is obese if his/her BMI is more than or equal to thirty kilogrammes per metre (kg/m2). There are degrees of obesity: class 1 (30.0–34.9 kg/m2), class 2 (35.0–39.9 kg/m2) and class 3 (more than or equal to 40 kg/m2). Alternatively, although less commonly used, parameters for the assessment of obesity include waist circumference and waist to hip ratio. A waist circumference of more than eighty centimetres in women is an accepted indicator of abdominal fat accumulation and also referred to as central obesity. A high body mass index is associated with reduced fertility and increased risk of complications in pregnancy. The likelihood of pregnancy declines with increasing BMI. In some countries, an obese person is denied fertility treatment.

According to the Europepub Med Journal, a study of 26,638 women ages 20 to 40 conducted to determine the association between obesity, menstrual abnormalities, and the ability to conceive. We now know that women with cycles without ovulation, i.e., irregular periods higher than thirty-six days, and hirsutism (male-like hair growth), was more than 30 pounds (13.6 kg) heavier than women with no menstrual abnormalities after adjusting for height and age. The study also concluded that the more overweight or obese a woman is, the more likely that she would have anovulatory cycles. Women with a single menstrual abnormality, including cycles higher than 36 days, irregular cycles, virile growing hair, with facial hair, or heavy flow were also significantly heavier than women with average values for these factors. A longer duration of high Body Mass Index was associated with facial hair. Another analysis found that teenage obesity was higher for never-pregnant married women than for previously pregnant married women, and for women having ovarian surgery for polycystic ovary syndrome than for women having ovarian surgery for other reasons. It also supports an association of obesity with anovulatory cycles. These findings showing evidence of abnormal ovulation, menstrual abnormalities, and excess hair growth in obese women may be explained by other recent studies demonstrating an association between obesity and hormonal imbalances.

The American Journal of the National Institutes of Health corroborates this when it reports that fertility can be negatively affected by obesity. In women, early onset of obesity favours the development of menses irregularities, chronic oligo-anovulation (reduced to absent ovulation), and infertility in the adult age. Studies presented by members of the WHO convention for setting guidelines for infertility treatments this year also supports that a high BMI increases the risk of complication in pregnancy s. Regardless of their method of conception, overweight or obese women have an increased risk of pre-eclampsia, gestational diabetes, miscarriage, stillbirth, and premature babies, and perinatal death. They also have a small increase in the risk of congenital fetal anomalies. Obesity in women can also increase the risk of miscarriages and reduce the success of assisted reproductive technologies. Obese couples are likely to have insulin in excess and be insulin resistant.

In men, obesity is associated with low testosterone levels. In massively obese men, reduced spermatogenesis (formation of sperms) associated with severely low testosterone levels may favour infertility. Moreover, the frequency of erectile dysfunction increases with increasing body mass index.

Obese women, particularly those with central obesity, are less likely to conceive per menstrual cycle. Obese women suffer disturbances to the hypothalamic-pituitary-ovarian axis (which is very important for reproductive function), women who are suffering from menstrual cycle disturbances are up to three times more likely to experience reduced numbers of or absent ovulatory cycles. Their periods may stop, or they may even have their periods but fail to ovulate; that is, they will not produce any eggs. Leptin, a hormone produced by adipocytes (fat cells), is elevated in obese women. Raised leptin is associated with reduced fertility. Obesity negatively affects ovulation, harms the development of the endometrium, which is the lining of the uterus. It can affect the implantation of the embryo so that even when fertilisation does occur, attachment of the embryo to the womb is a problem. Obese women can get pregnant but will have several complications, including high blood pressure, with the danger of eclampsia leading to convulsions.

Much more attention devoted to the impact of obesity on fertility in both women and men. It appears to be particularly important for women before assisted reproductive technologies are used. Treatment of obesity may improve androgen imbalance and erectile dysfunction, the major causes of infertility in obese men.

Professor Oladapo Ashiru

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