Weight gain during pregnancy: how much is too much?

During a healthy pregnancy, women gain weight as the baby grows. This is normal and necessary.

But recent research indicates that excessive weight gain during pregnancy increases health risks for mothers and their children.

So how do you get the right balance?

Recommended weight gain in pregnancy is based on body weight and body mass index (BMI) prior to becoming pregnant. If your pre-pregnancy BMI is:

• less than 18.5, aim to gain between 12.5 and 18 kg
• 18.5 to 24.9, aim to gain 11.5 to 16 kg
• 25.0 to 29.9, aim to gain 7 to 11.5 kg
• 30 or more, aim to gain just 5 to 9 kg.

Most weight gain occurs from week 13. For some women, body weight will not change too much during the first trimester of pregnancy, particularly for women who have had morning (noon and night) sickness.

Weight gain recommendations are higher for those having twins, with the target range depending on the woman’s pre-pregnancy BMI: 18.5-24.9 (weight gain: 17-25 kg), 25-29.9 (weight gain: 14-23 kg) and 30 or more (weight gain: 11-19 kg).

A recent review covering more than one million pregnancies found half the women gained too much weight. Even women who started pregnancy at a healthy weight (those with a BMI of 18.5 to 24.9) typically gained too much weight.

Our study of women in the United Kingdom found excessive weight gain was more common among women who were having their first baby.

Gaining too much weight in pregnancy can affect the mother’s health. Excess weight gain has been linked to a higher risk of developing diabetes in pregnancy, high blood pressure, and complications during birth.

It can also affect the health of the baby in both the short-term and in the future. In a review of one million pregnancies, mothers who gained too much weight in pregnancy were more likely to have babies with a high birth weight compared to other mothers. Children of the mothers who gained too much weight were then at a higher risk of becoming obese as a child or adult.

Excess pregnancy weight gain can also make it more challenging to lose weight after the baby is born. Our recent study showed that women who gained more weight than recommended retained, on average, an extra 4kg six months after their baby was born. Of concern is that this extra weight can still be retained decades after pregnancy. Not shifting those extra few kilos after pregnancy increases the chances of developing obesity in the future.

Not gaining enough weight in pregnancy can also be a problem. Weight gain below the recommendations is associated with having a baby that is small for gestational age, or a preterm birth.

It’s important for women not to try and lose weight during pregnancy. Dieting or limiting food intake could mean the baby doesn’t get enough nutrients needed for their development.

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