Woman holding her pregnant belly Woman holding her pregnant belly

Pregnancy weight gain

Every woman is an individual and unique. Genetics, gender, age, environment, diet, occupation, lifestyle factors and metabolism all play a role in what any of us weigh and how much weight we gain or lose over our lifetimes. 

Most women who are within an average height and weight range at the start of their pregnancy  can expect to gain between 10-15 kilograms over the full 40 weeks of gestation. This can be more in cases of multiple pregnancies or if there are some pregnancy complications. 

The majority of pregnant women have a very small weight gain within their first trimester and some will even lose weight. Nausea, combined with changes in the normal eating pattern, can mean a weight loss of up to a couple of kilograms. However, during the second and third trimesters, most women regain what they may have lost and gradually start to gain more. 

But don’t I have to eat for two? 

The old saying of pregnant women needing to eat for two has no scientific basis. In fact, doubling portion sizes and increasing food volume during pregnancy is not only unnecessary, it can be dangerous. What is needed is not so much an increase in food intake, but a doubling of nutrition quality. These are two very separate things. 

Most pregnant women only need to increase their kilojoule intake by around 10%. During the first trimester this means an extra 420 kilojoules/day, during the second trimester an extra 1050 kilojoules/day and in the third trimester, an extra 1255 kilojoules/day. 

Broken down, this means in the first trimester the extra kilojoules could be met by a glass of low fat milk a day, in the second trimester by some nuts and an extra piece of fruit a day and in the third trimester, some fruit and an extra piece of bread per day. 

Where does the extra weight come from? 

Pregnancy weight gain can be divided into how much the mother contributes to her overall gain and what her baby does. It is considered fairly normal for most women to gain around 3 kg of extra body fat over the course of a normal pregnancy. Extra weight deposits around their thighs, hips, bottom and arms act as reservoirs or energy stores which can be used by the body during breastfeeding. 

Maternal weight gain comes from:

  • Extra circulating blood volume

  • Water retention and general fluid increase

  • Extra weight of the breasts

  • Extra weight of the expanding uterus

  • Amniotic fluid and placenta

  • The baby (at birth an average weight is around 3.5 kg) 

In the early stages of pregnancy, most maternal weight gain is as a result of changes within the mother, rather than the baby. More blood is produced to support the growing foetus and to supply it with the oxygen and nutrients it relies on to grow. 

It is normal for there to be fluctuations and changes in a pregnant mother’s weight gain. But any sudden increase or decrease can be cause for concern. This is why most midwives and obstetricians monitor the weight gain of their clients as it is an indicator of some complications. 

A lot of pregnant women like to keep a check on their weight themselves and the best way to do this is with a weekly weigh, at around the same time of the day. The ideal way to gain pregnancy weight is slowly and steadily.

A gain of more than 1.5 kg in one week in the second trimester or a gain of more than 900 grams in one week in the third trimester, is reason enough to check with your midwife or doctor. 

A guide for average weight gain in each trimester:

  • First Trimester: 900 grams – 1.8 kilograms total

  • Second Trimester: 500 grams/week from 4-6 months to a total of 5-6 kg

  • Third Trimester: Around 500 grams/week to a total of 3-5 kg 

What’s a BMI?

Some midwives and doctors use the BMI (body mass index) to estimate the ideal weight gain during pregnancy. This is a measurement of an individual’s body fat, which is worked out using a mathematical formula, i.e. weight in kilograms divided by height in metres squared. An average BMI is between 18.5 to 26. Having a high or low BMI can influence the advice offered by healthcare providers regarding how much food a pregnant woman should be eating each day. 

How long will it take to lose it?

Many experts agree that it is fair to assume what took 9 months to gain, will take around the same period of time to lose. Some women just drop their pregnancy weight so quickly, they are back in their pre-pregnancy clothes within a couple of weeks of giving birth. Others take longer. 

The same basic maths for losing weight at any other time, applies equally after birth. The more energy that is taken into the body in the form of food (fuel) the more needs to be used up. Too much food for the amount that is being used, is stored as fat. To lose excess weight requires some attention to portion control and some form of daily exercise. 

What about dieting?

Pregnancy is not a time for any woman to diet. Kilojoule restriction can lead to malnutrition and may affect the baby’s growth. There is also an increased incidence of neonatal death and low birth-weight babies in women who diet during their pregnancy. Losing weight too quickly after birth can lead to problems with low lactation and flagging energy levels. 

Being underweight during pregnancy can lead to problems with:

  • Having a small and underweight baby at birth

  • Increased risk of premature delivery and the associated problems with having a pre-term baby

  • Potential problems with lactation and low breast milk supply 

Having a BMI that is too low or being very underweight can also lead to problems conceiving. A normal menstrual cycle is dependent on having a healthy ratio of fat to lean muscle and an adequate daily food intake. 

Being overweight during pregnancy can lead to problems with:

  • Higher risk of problems with labour and delivery

  • An overweight baby that may have problems regulating its blood sugar levels, and associated problems with delivering a larger baby

  • Haemorrhoids, stretch marks, pelvic floor problems, urinary incontinence

  • Feeling more uncomfortable and becoming heat intolerant

  • Backaches, leg aches, swollen feet and ankles and problems with mobility

  • Raised blood pressure, higher incidence of Pre-eclampsia, and an increased risk of developing gestational diabetes

  • Extra strain on the vital organs such as the heart, liver and kidneys

  • Higher incidence of insulin resistance and type 2 diabetes 

The best advice regarding weight gain during pregnancy is to think in terms of the quality of the food you are eating, not the quantity. While your baby is in your uterus, it depends fully on you to supply it with all the nutrients and elements it needs to grow. 

Bodies that are carrying too much fat don’t work as effectively as they should. The toll of excess weight on energy, mood and general health is too high just for the sake of eating too much. 

Learn to listen to your body’s signals that it is full and your stomach has enough food in it. 
Try to think in terms of being satiated during meals, meaning your hunger is satisfied and you do not need to eat any more. Avoid missing meals as this can put your body into a “starvation mode”, which leads to issues with metabolism and low energy.


If you would like to know more If you would like to know more
Name should not be blank