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 normal babies.
Getting pregnant is not so easy, even for couples who have normal physiological parameters. For example, a couple who has no medical abnormalities and who has normal weight, with a body mass index of 19-25 kg/m2, has only 80 percent chance of getting pregnant within one year of having unprotected sex. This 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 effects of obesity on key 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 is characterised by excess fat storage. Definitions of obesity can vary, but the most widely accepted definition is that of the World Health Organisation’s BMI (kg/m2) criteria.
A person is obese if his/her BMI is more than or equal to 30 kg 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 80 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, fertility treatment is denied to obese persons.
According to the Europepub Med Journal, a study of 26,638 women ages 20 to 40 was conducted to determine the association between obesity, menstrual abnormalities and infertility. It was found that women with anovulatory cycles i.e., irregular cycles greater than 36 days, and hirsutism (male-like hair growth), were 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 greater than 36 days, irregular cycles, virile hair growth with facial hair, or heavy flow were also significantly heavier than women with normal values for these factors.
A longer duration of obesity was associated with facial hair. Another analysis found that teenage obesity was greater for never-pregnant married women than for previously pregnant married women, and for women having ovarian surgery for polycystic ovaries than for women having ovarian surgery for other reasons.
This 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 adulthood.
Studies presented by members of the WHO convention for setting guidelines for infertility treatments this year also support that a high BMI increases the risk of complications in pregnancy. Regardless of their method of conception, overweight or obese women have an increased risk of pre-eclampsia, gestational diabetes, miscarriage, stillbirth, premature babies and perinatal death. They also have a small increase in the risk of congenital foetal 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. These factors are at the root cause of their reduced fertility and decrease in the success of their having a live, healthy baby. These adverse effects of obesity are specifically evident in polycystic ovary syndrome, which is a major cause of infertility.
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 suffer reduced numbers of or totally 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 has been associated with reduced fertility. Obesity has also been observed to have a negative impact on the development of the lining of the uterus (endometrium). This can affect implantation of the embryo so that even when fertilisation does occur, attachment of the embryo to the womb is a problem.