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Weight gain during pregnancy

Hadyn Luke posted this on Tuesday 26th of March 2013 Hadyn Luke 26/03/2013

Tags: Special populations


Weight gain during pregnancy

Today’s blog investigates why it’s important for women to gain weight during pregnancy and what they should expect across the three trimesters. 

During pregnancy, the body goes through key physiological changes, one of which is weight gain. Personal trainers will often have female clients who are concerned about weight gain but there are good reasons why they should not skimp on calories and nutrition during pregnancy.

Calorie intake during the different trimesters of pregnancy

The trimesters in pregnancy are as follows:

First trimester: 0-13 weeks

Second trimester: 14-27 weeks

Third trimester: 28-41 weeks

Pregnant women often talk about “eating for two” and indeed calorie intake should be increased by 150 calories a day during the second trimester and 300 calories during the third trimester, when the baby is growing exponentially. 

Breaking down weight gain during pregnancy

It’s important that a personal trainer reassures clients that they are putting on baby weight rather than “getting fat”. It may be helpful to break this down into the amount of weight a healthy woman is expected to put on during pregnancy. 

In the first trimester there is an increase in insulin resistance, which leads to maternal fat storage. In the first and second trimester, the weight gain should be around 7-11lbs (3-5kg), which again is mostly maternal body fat. The third trimester sees more rapid weight gain, as much as 1lb (0.4kg) per week, which is largely because of the increased foetal growth rate. In total, the weight gain should be 24-33lb (11kg-15kg). 

Weight gain is distributed as follows: 

  • Baby 8lb (3.6kg)
  • Placenta 2lb 3oz (1kg)
  • Amniotic fluid 2lb 3oz (1kg)
  • Breast tissue 2lb 3oz (1kg)
  • Blood supply 4lb (1.8kg)
  • Fat stores for delivery and breastfeeding 5lb –  8lb 13oz (2.3-4kg)
  • Uterus increase 2lb 3oz – 5lb (1-2.3kg)

Insulin resistance during pregnancy

Insulin resistance is increased during pregnancy, indeed the effect that pregnancy has on insulin is similar to a mild case of diabetes. One in 300 pregnant women develop gestational diabetes, but those who are physically active in the pre-natal period are less likely to have this condition. A fitness professional should make their female clients aware of this fact if they are looking to fall pregnant and considering whether to continue exercising.

During mid- to late pregnancy, the mother-to-be will start to utilise fat as her primary energy source rather than her glycogen store. By doing this she will become more oxidative (fat dependent), and the carbohydrates she ingests will be broken down into glucose, which is transported in nutrients to help the baby grow and develop and to supply the placenta.

The risks of insufficient weight gain during pregnancy

In a study reported in the Obstetrics & Gynecology journal (2000; 96:194-200) under the heading “Prepregnancy Body Mass Index and Pregnancy Weight Gain: Associations with Preterm Delivery”, the reported conclusion was as follows:

“Low weight gain in pregnancy was associated with increased risk of preterm delivery, particularly if women were underweight or of average weight before pregnancy.”

This relates in particular to women under 18.5 on the BMI scale who don’t gain the required weight.

Premature birth is not only a risk for the child at the point it is born, but it can result in health problems in later years 

If a woman keeps active during pregnancy and eats a healthy diet, she will increase her chances of having a healthy pregnancy and will find it easier to lose any weight gained during this time once the baby is born.


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