Obesity, Fertility & Pregnancy

The prevalence of excess weight and its extreme obesity, has more than doubled in Australia in the past 20 years. Experts are linking the rise to sedentary lifestyles and a lack of education.

The prevalence of excess weight and its extreme obesity, has more than doubled in Australia in the past 20 years. Experts are linking the rise to sedentary lifestyles and a lack of education. A recent Australian Diabetes, Obesity and Lifestyle Study found that Body Mass Index (BMI) or waist circumference considered almost 60% of men and women overweight or obese as defined.
BMI is a formula used universally that identifies the percentage of body tissue that is actually fat by taking your weight in kilograms and dividing it by the square of your height in metres.

Obesity is generally defined as weighing more than 20% above the expected weight in relation to your age, height and body build. This equates to an excess of approximately 15.9kg or 35 lbs or a BMI of 30-40.


How does excess weight and obesity affect fertility?

Excess weight and obesity affects fertility by causing hormonal imbalances that have an impact on ovulation and menstruation. Being overweight is thought to account for around 10% of infertility cases.

Fat cells produce the hormone estrogen in the form of estrone – E. When there is too much estrogen in your body, it responds as though you are on the contraceptive pill. Often this prevents the egg being released from the ovary and therefore it is impossible for conception to take place.
In some cases an egg may be released but hormonal disturbances may not be adequate enough to support the rest of the cycle.

Polycystic Ovary Syndrome

The condition polycystic ovary syndrome (PCOS) is closely associated with excess weight and obesity. This is a hormonal, or ‘endocrine’ disorder with any combination of the following symptoms:

  • Irregular cycles
  • cysts in the ovaries
  • pain whilst ovulating
  • failure to ovulate
  • heavy and painful periods
  • acne
  • excess body hair on the face, chest, below the navel and toes, and
  • a high LH-FSH ratio greater than 3:1

If you are experiencing a combination of these symptoms and suspect that you may have PCOS contact your health specialist. Diagnosis may involve a physical examination and an ultrasound to check the health of the ovaries and the blood flow.

Weight Distribution

A study published in the British Medical Journal found that women with a BMI greater than 38 had lower rates of conception.
While BMI is an acceptable method the study found that in this instance the distribution of body fat had a greater impact on fertility.

The study concluded that women with a high waist-hip ratio had more trouble conceiving. Therefore being shaped like an apple is not as good for conception having a pear-shaped figure.

Pregnancy & Obesity

For many women pregnancy is a time when weight comes under scrutiny.
Beginning a pregnancy with excess weight or gaining excessive weight during pregnancy increases the risk of complications.

Excess weight often causes breathlessness, lethargy, increased abdominal pressure, indigestion, heartburn, depression and added physical pressure on knee joints as the pregnancy progresses.

If your weight gain is more significant you may develop gestational diabetes or pre-eclampsia. Both conditions are serious and your health professional must be advised.

Gestational Diabetes

Gestational diabetes is diagnosed when there are high blood sugar levels during pregnancy. The body’s need for insulin, the hormone that controls the level of sugar in the blood, increases and sometimes there is not the reserve to make the extra required to balance the levels. This is when diabetes develops. Symptoms include extreme thirst, frequent urination and fatigue. If you experience these symptoms, contact your health professional. For many women the first they know of gestational diabetes is sugar in the urine, detected via a routine urine test.


Pre-eclampsia affects between 5-10% of all pregnant women. Known as "the disease of theories" the causes are not clearly known although poor nutrition is thought to be a key factor.

Pre-eclampsia must be treated seriously as it affects the placenta reducing blood and oxygen supply to the baby. If the condition is allowed to progress, clots and fatty acids build up in the placenta blocking the arteries and causing placental failure.

In its most severe form, it is known as eclampsia.


There is evidence that women who are overweight or obese may carry larger babies and may not carry to full term. They may be more likely to have labour complications requiring intervention involving anaesthesia and/or Caesarean section.

Obesity and Miscarriage

Although excess weight is not thought to contribute to miscarriage, the condition PCOS, which is common in overweight women, is associated with a greater statistical chance of pregnancy loss than normal because of hormone imbalance.

Professional Help

Pregnancy brings an urgent need to address weight problems or poor eating habits. This includes under-eating as well as compulsive over-eating and addictions.
If your problem is due to an eating disorder you are likely to receive the help you need if your medical professionals know about the problem you have.

For most women it is very difficult if not impossible to resolve eating difficulties without professional help and there is no reason why you should feel obliged to sort out these issues alone. Help is out there to assist you during this time.

It is important to note that a slight weight gain is unlikely to place your health and the health of your baby in danger especially if you are eating a well-balanced diet that would provide all the nourishment you need. If you are unsure about your weight contact your health professional for advice.

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