Pregnancy and Weight Control

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Women who are very overweight (or very underweight) at the start of pregnancy are at greater risk of developing complications during pregnancy or at delivery. For the overweight woman, these include high blood pressure, hypertension or pregnancy (toxaemia), caesarean birth, kidney ailments, gestational diabetes and a long labour.

If you’re pregnant or considering pregnancy, make sure you have a good understanding of what’s what when it comes to weight.

Weight gains during pregnancy

Mother’s pre-pregnancy weight, and how much weight she gains during pregnancy, have a major effect on the size of the baby. While having too large a baby may increase the baby’s risk of becoming obese, it is equally if not more important to reduce the risk of a low birthweight infant.

Too low a birthweight (less than 2.5 kg/5.5 lbs) increases the risk of birth defects and other health problems. The optimal birthweight is now considered to be 3,200 – 4,500 grams (7 – 10lbs).

Generally, the lower the weight gain in pregnancy, the lower the birthweight. This is true for all women – even in obese women. Underweight women need to gain the most weight during pregnancy and obese women the least. Some guidelines follow.

  • Ideal Weight Gain: A total weight gain of 11 – 16 kg during pregnancy is desirable. Normally, only 1.5 – 2 kg is gained in the first trimester (12 weeks). Thereafter, an average of 0.4 kg each week.
  • Excessive Weight Gain: Weight gain of over 16 kg during pregnancy may result in too large a baby. A sudden increase in weight might result from toxaemia or excess calorie intake. Dietary changes to control weight gains are best supervised by an obstetrician and dietitian. Pregnancy is not the time for extreme dieting as foetal growth can be impaired.
  • Inadequate Weight Gain: Weight gain of less than 7 kg, is more likely to result in a low birthweight baby. The past practise of over-restricting food intake to limit weight gains is no longer considered healthy. Too little weight gain, even in obese women, indicates that the dietary intake is too low to provide adequate nutrition for optimal development of the growing baby and the maintenance of mother’s health.
  • Teenagers are a high risk group for low birthweight infants. Unlike older mothers, growing teenagers may need to ‘eat for two’, to accommodate their own needs as well as those of the foetus. A weight gain of 13 – 16 kg will minimise the risk of a teenager having a low birthweight baby. Under no circumstances should a growing teenager view pregnancy as an opportunity to lose weight.
Acceptable Weight Gains During Pregnancy
Underweight: Gain 13 – 18 kg
Normal Weight: Gain 11 – 16 kg
Moderately Obese: Gain 9 – 11 kg
Very Obese: Gain 7 – 9 kg

Components of weight gain

Only 3.5 kg of the total weight gain is due to the developing baby. The remainder is comprised of vital tissues and fluids that nourish and protect the foetus before and after birth.

The components of weight gain are:

Developing baby (foetus)

Placenta

Amniotic fluid

Extra breast tissue

Extra blood

Fluid

Uterus

Fat stores

3 – 4 kg

0.5 – 1 kg

1 – 1.5 kg

0.5 – 1 kg

1.5 – 2 kg

1 – 1.5 kg

1 – 1.5 kg

1.5 – 3 kg

Approximate total weight gain 10 – 15.5 kg

Importance of fat reserves

The fat stores that the expectant mother lays down during pregnancy have important roles. They act as a safeguard against any periods of food shortage.

The energy stored in the fat is also used in producing breast-milk. Additionally, body fat insulates and protects the growing baby. The fat stores of 1.5 – 3 kg represent approximately 25,000 calories and can subsidise the extra metabolic needs of late pregnancy and breast feeding. These fat stores may not be fully used and this may contribute to residual weight gain after each pregnancy.

Calorie requirements during pregnancy

Energy requirements during pregnancy vary considerably from person to person. This reflects wide differences in the body’s energy needs and the amount of exercise performed. Extra calorie requirements are not huge, usually only 100 – 300 extra calories each day.

In women who substantially reduce their exercise, the need for extra calories may be minimal. Even towards the end of the pregnancy only 2400 calories daily is needed by the average woman (talking 2100 calories as the needs of the average non pregnant woman).

While few extra calories are required during pregnancy, there is a greater demand for extra nutrients. It is important to choose nutrient-dense foods, and to avoid high fat, and calorie-dense foods such as biscuits, confectionery and soft drinks.

Vitamin/mineral supplementation, particularly of iron, folic acid and zinc is usually prescribed as a safeguard.

Extra calories required

(Normal weight and activity level)

1st Trimester 100 – 150 calories

(e.g. 1 large banana)

2nd Trimester 200 – 300 calories

(e.g. 2 crackers/cheese)

3rd Trimester 300 calories

(e.g. 1 chicken sandwich)

Hazards of dieting during pregnancy

Pregnancy is not a good time to attempt weight loss, as the health of the growing foetus is at risk.

  • Inadequate energy intake could ‘starve’ the foetus of nutrients, especially in the third trimester, and increase the risk of a low birthweight baby.
  • Excessive weight loss can produce ketones, a by-product of fat breakdown, that may be detrimental to the baby’s development.
  • The mother runs the risk of ill-health both during pregnancy and in subsequent years. For example, inadequate calcium will increase the risk of osteoporosis (brittle bones) in later years.
  • Unbalanced nutrition during pregnancy can severely affect milk production during lactation. Adequate protein and energy is required for optimal growth of the mammary glands. Even adequate nutrition during lactation may not overcome the lack of mammary gland growth that occurred during pregnancy.

Healthy eating habits acquired during pregnancy and breast feeding can form the basis of any necessary weight loss program after the birth of the baby. If a mother breast feeds her baby for at least 4 – 6 months, she will find that by 12 months her weight should return to pre-pregnancy levels.

Extra notes and hints

Moderate exercise during pregnancy is beneficial. Swimming, walking and the exercise bike are excellent activities that are unlikely to overstress the body. Very strenuous activity is not advised as it may divert oxygen from the foetus to the exercising muscles. Lifting and carrying heavy objects should also be avoided. If any health problem is present, do not exercise without medical advice.

During pregnancy extra iron is required for the increase in mother’s blood volume and for normal growth of the foetus and placenta. Since it can be difficult to get the recommended amounts of iron from food, a daily supplement is prescribed during the 2nd and 3rd trimester. The extra iron promotes adequate stores in the mother to be used in breastfeeding.

Folate is required for the production of new cells in the foetus and placenta. A folate supplement is usually given in conjunction with iron.

Excess Alcohol can deplete the body of essential nutrients and can cause defects in the foetus. It is strongly advised not to drink alcohol during pregnancy.

Cigarette Smoking can constrict blood vessels supplying the placenta and reduce the nutrient supply to the growing baby. Smoking will also reduce oxygen supply to the developing baby. Please do not smoke during pregnancy.

Calorie King
CalorieKing's mission is to provide the best information, tools and education to Australians to help them conquer their weight.

CalorieKing is the brainchild of Allan Borushek, registered dietitian, co-found here at food.com.au and author of "Allan Borushek's Pocket Calorie & Fat Counter", Australia's best-selling calorie counter for over 30 years.

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