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| Oladapo Ashiru |
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.
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