Nutrition
Weight gain in pregnancy
Did you know?
Women who are breastfeeding their infants should consume an additional 2000-2100kJ per day.
News in a hurry
- When pregnant, continue to eat a variety of foods according to your appetite and do not restrict your energy intake, unless you are already obese or gaining weight at a higher rate than recommended (see below).
- Estimated energy requirements for all ages in pregnancy: 1st trimester, no additional requirement (total: 8000-10,000kJ/day); 2nd trimester, additional 1400 kJ/day; 3rd trimester, additional 1,900 kJ/day.
- If you have a BMI that's below 19.8 or above 30 at the start of pregnancy it’s recommended you receive advice from a dietitian.
- As part of your antenatal care you should receive: an individualised recommendation for energy intake, with particular focus on the second and third trimesters, and regular monitoring of your weight.
- Weight gain is much lower in the first than the second and third trimesters.
- Weight gain in the first half of pregnancy can affect the baby's growth throughout pregnancy.
- The first half of pregnancy is considered the preparation for later growth of the baby.
- 90% of the baby's growth happens in the second half of pregnancy.
- Maternal fat stores (average 3.3kg) are mainly gained between weeks 10 and 30.
- For women with a normal BMI before pregnancy, in the second and third trimesters a weight gain of 0.4kg per week is about right (0.5kg for underweight; 0.3kg for overweight; obese women need individualized advice)
Recommended weight gain, according to pre-pregnancy BMI
| Pre-pregnancy BMI |
Recommended total weight gain |
| Below 19.8 |
12.5 to 18kg |
| 19.8 to 26 |
11.5 to 16kg |
| 26 to 29 |
7 to 11kg |
| Over 29 |
6kg |
NB¹: These are known as the IOM recommendations and are the basis for the Ministry of Health’s recommendations for weight gain in pregnancy.
NB²: Body mass index is your weight divided by your height squared. BMI tends to relate to fat mass on the body but, for active or more muscular women, BMI may overestimate this. People of Asian origin tend to carry a higher fat mass for a given BMI, and those of Polynesian origin have a proportionately lower fat mass for a given BMI. The table’s recommendations may be affected by these ethnic differences.
How much energy do I need to include in my diet?
Achieving an ideal weight gain during pregnancy benefits you and your baby. The recommended weight gain during pregnancy, and the agreed amount of energy needed in the diet, will differ from woman to woman - both depends on body 'size' before pregnancy.
Weight gain in pregnancy is made up of the developing foetus, placenta and amniotic fluid increases in volume of the woman's own body (uterus, breasts, blood and cell fluid) increases in the woman's fat stores.
NZ Food and Nutrition Guidelines for healthy pregnant and breastfeeding women
On average, energy requirements increase by 12% during pregnancy. In the first trimester, there is little or no need for extra energy but, by the third trimester, you will have a higher rate of metabolism due to the rapidly growing baby and the effect of your own extra bodyweight – so you will need extra calories in your diet.
However, this need may be offset because you may become less active later in pregnancy and so burn less energy.
For well-nourished women, the optimum weight gain in pregnancy can be achieved with widely varying energy intakes. The right amount of energy in the diet is much more important for women who are underweight or overweight before pregnancy.
Who should seek expert advice?
If you have a BMI that is below 19.8 or above 30 at the start of pregnancy it’s recommended you receive advice from a registered dietitian.
If you’re undernourished, or still an adolescent, when you fall pregnant, and you restrict your calorie intake, your body will take the nutrients it needs first, compromising the growth of the baby, and raising the chances of a pre-term delivery.
If you are already overweight and you gain too much weight pregnancy, you can increase the chances of having a very large baby, ie, over 4kg.
Talk to your LMC or dietitian
Your lead maternity carer or dietitian should be able to advise you on the energy requirements that are right for you. They can also ensure the quality of your diet is the best it can be for your pregnancy - quality is every bit as important as quantity.
Pre-pregnancy weight and weight gained during pregnancy are related
It seems young, short, thin women, and smokers, gain less weight, while tall, heavy women, especially when having their first child, or they have high blood pressure, gain more weight in pregnancy. Also, the more weight gained the more seems to be retained after the pregnancy - this because, once over the recommended weight gain, the weight that goes on is mainly fat.
For women in the ideal range of BMI before pregnancy, there are recommended average increases in energy intake for the three trimesters of pregnancy (1st, no extra energy; 2nd, +1400kJ or + 340kcal per day; 3rd, +1900kJ or +450kcal per day), but care needs to be taken in applying these to individual women.
A brief history of advice given to healthy pregnant women
Many years ago pregnant women were advised to eat for 2.Then, in a complete change, they were advised to restrict food to avoid excess weight gain in order to prevent toxaemia of pregnancy (pre-eclampsia), difficult births and maternal obesity.
This was challenged in the 1960s when the detrimental effects of a low birth weight on infant health were recognised. Pregnant women were then advised against severe calorie restriction and routine limitations on weight gain.
In the 1970s, a large study managed to establish the 'normal' weight gain during pregnancy and the weight gain associated with the best outcomes for mother and baby. In pregnant women who ate without restricting their diet, it was found the total weight gain of 12.5kg was associated with the best outcome in terms of birth weight, infant survival and rates of pre-eclampsia.
In 1990, a US report for the Institute of Medicine (IOM) Food and Nutrition Board returned to the relationship between pregnancy weight gain and the best outcome for infants (in terms of birth weight) and for mothers (in terms of delivery complications and retaining the extra bodyweight after giving birth). Importantly, it showed that, because the weight gained during pregnancy actually influences your energy requirement, your BMI should be taken into account when making dietary recommendations.
See our BMI calculator.