My feed

Weight gain in pregnancy

Weight gain during pregnancy is one of life's certainties, but studies show that many women don't know how much weight they should be putting on – and could be putting themselves and their baby at risk

By Mumsnet HQ | Last updated Jul 16, 2021

pregnant woman standing on scales

Some women find it a pleasant change to be able to 'let it all hang out' and no longer worry about having a bit of a tummy, while others find the changes to their body make them feel strangely out of control. While you should avoid gaining too much weight, a certain amount is a sign that everything is as it should be so try and accept it, even if you can't fully embrace it (and even if no one can 'fully embrace' you as your bump grows).

How much weight gain is normal during pregnancy?

Several factors determine how much weight you will put on during pregnancy: your pre-pregnancy weight, the amount you eat and your genetic make-up being just some of them. The NHS estimates that the average woman with a healthy BMI will put on around 22-28lb (10-12.5kg) and most of this is after week 20.

To get an idea of how much weight you should ideally be gaining during pregnancy, first work out your BMI. Divide your weight in kilograms by your height in metres then divide the answer by your height again to get your BMI. Or you can use an online calculator to get the number.

Once you have your BMI, the chart below will tell you how much weight gain you should be aiming for.

How much weight you should gain during pregnancy:

  • BMI less than 19.8 – 28lb to 40lb

  • BMI 19.8-26 – 25lb to 35lb

  • BMI 26.1-29 – 15lb to 25lb

  • BMI more than 29 – 15lb

If you're gaining a bit more or less than this, don’t panic. Everyone is built differently and your midwife will be keeping an eye on any sudden weight gain or loss. You can always ask at one of your appointments if you have any concerns.

What makes up the weight you gain in pregnancy?

The rest of it will be:

  • Your breasts, which alone can put on more than 1kg (3lb) as they prepare for breastfeeding

  • Increased blood volume

  • Extra fluid in the body

  • An increase in the muscle layer of the uterus

  • Increased fat stores

I gained five stone with three of my pregnancies and had lost it all by the time they were nine months. Have excelled myself this time round – six-and-a-half-stone gain, he's six weeks old and have lost four stone already. I get a lot of water retention! About a third of your weight gain by the time you reach your due date is made up of your baby, placenta and the amniotic fluid.

When do you start to gain weight in pregnancy?

This differs from one woman to the next. Most of the weight gain happens after 20 weeks, when the baby starts to grow much more quickly. During the first trimester some women actually lose weight due to pregnancy sickness or just going off lots of foods.

Pregnant woman measuring bump

How much weight will I gain in the first trimester?

An average weight gain during the first trimester is about 5lb – so you might not look that different at all by 12 weeks. If you’re very sick in the early days and weeks, you might even find you lose weight in the first three months. Lots of women report that simply cutting out the booze and eating more healthily sees off a few pounds, too!

How much weight will I gain in the second trimester?

There's a lot of variation, dependent on your metabolism, the size of your baby and what your weight was pre-pregnancy (the heavier you were to begin with the less you can expect to gain) but on average, women gain around 1lb a week in months three to six. The key is to keep your weight gain as steady as possible. Gaining at a slower pace might help you to avoid stretchmarks, too.

How much weight will I gain in the third trimester?

Ideally, you'll keep putting on weight at an average of 1lb a week in the last three months. By this stage though your baby is really laying down the pounds herself, so you'll need a little bit more fuel yourself – about 200 calories extra per day (that's an extra slice of toast and butter and a large banana).

How much weight will I put on if I’m having twins?

If you're carrying twins you can typically expect to gain around 50% more than you would with a single baby. It may well feel like more than double, however.

How can I control my weight in pregnancy?

You don't want to gain no weight at all, the main thing is to try and keep weight gain steady – it's all about common sense. Aim for a balanced diet of fruit, veg, carbohydrates, protein, fish, lean meats – and not too much red meat, sugars and excessively fatty or over-processed foods.

Make sure you're up to date on all the various dos and don’ts of pregnancy in terms of what you should be eating. And try to eat smaller meals, which you might want to do anyway if you're suffering from heartburn.

The eating for two thing, while being a good excuse to indulge, should really be discarded. You need to eat a bit more, yes, but don't go mad.

For the first two trimesters your calorie intake should be the same as before – around 2,000 calories a day. It's only in the third trimester that you'll need an extra 200 calories a day. Remember that extra 200 calories is better expended on a slice of toast and peanut butter or a small avocado than a four-finger KitKat, though.

I lost weight in the first half of the pregnancy. I probably had a bit to lose anyway, and I think the baby just “ate” the surplus! I always had a neat little bump and never got very big. There's a reason why they don't use weight gain any more as a measure of pregnancy progression – it's utterly variable.

What exercise can I do to keep weight gain steady in pregnancy?

Try to stay active, exercise moderately but regularly, drink plenty of water and take cues from your body about when and how much to exercise.

If you were fairly fit before, you should be able to carry on running or going to the gym (or whatever your preferred method of exercise was pre-pregnancy). If you were more couch sloth than gym bunny though, don't despair. There are lots of fantastic classes dedicated to pregnancy around, so now's a great time to get started.

pregnant woman doing exercise

Will I be weighed during pregnancy?

You'll be weighed as part of your booking-in appointment and have your BMI calculated. After that, you won't be weighed much at all unless you or your midwife have concerns about how much weight you are (or aren't) gaining. The midwives will measure your bump from time to time, and if they are concerned that the baby might be too big or too small you may be referred for an additional scan to have a closer look.

It used to be that women were weighed at every antenatal appointment but the NHS seems to have caught on that pregnancy can be nerve-wracking enough without being forced to step on the scales in public every few weeks.

I've started shopping at places that do great fruit and veg so I know I'm putting only good stuff into my body – and if I'm putting weight on then it's OK because I'm a bloody superwoman and I'm growing an actual human being in my belly!

What are the risks of gaining too much weight during pregnancy?

You should put on weight steadily throughout your pregnancy. Rapid weight gain can signify a problem such as pre-eclampsia so do ask your midwife if you have any concerns. Thwacking the weight on too fast can put you at greater risk of developing gestational diabetes and thrombosis, and you may be more likely to suffer heavy bleeding post birth.

Official advice from the Royal College of Obstetricians and Gynaecologists states, “It is a myth that women need to 'eat for two' during their pregnancy – energy needs do not change until the last three months of pregnancy, when women need an extra 200 calories a day. Having a normal bodyweight will help to increase the chances of conceiving naturally and reduces the risk of pregnancy and birth complications for the mother and baby.”

Excess weight gain can mean your baby is bigger and research also suggests that a baby who is big for their dates is more likely to run into problems such as shoulder dystocia during labour, making a Caesarean section more likely. Big babies are also more likely to have obesity later in life.

What are the risks of not gaining enough weight during pregnancy?

You might be surprised to know that not gaining enough weight in pregnancy might also mean your child is at greater risk of obesity in later life. You may also have an increased risk of having a small baby or premature birth.

What are the risks of being overweight or underweight before pregnancy?

Being underweight or overweight can sometimes have a detrimental effect on your ability to conceive, and then once you are pregnant, on the development of your baby.

Women who are malnourished before they become pregnant are more prone to things like:

  • Miscarriage

  • Premature birth

  • Having babies with a low birth-weight

Those who are overweight before they get pregnant run the risk of complications such as:

What should I do if I’m overweight and pregnant?

Your midwife or GP will be able to give you advice if you are either underweight or overweight. Try to eat sensibly and healthily and on no account try to lose weight once you're pregnant. You should be looking more at being active and swapping healthy foods in for less 'good for you' alternatives.

If you're already diabetic before pregnancy, you could ask your diabetes nurse to review your diet before trying to conceive and check whether you should be taking a higher dose of folic acid – some women with a high BMI are advised to do this. If you're already pregnant and diabetic, make sure your midwives are aware so that you get all the appropriate care you're entitled to.

In my first pregnancy I started at about 9st 2, went down to 8st 7 from first trimester nausea, then in five months when food became tolerable again ballooned rapidly to 13st. At 5ft 2, I looked like a weeble with size 8 shoulders and a 43 inch waistline! I lost it all within a year though.

When will I lose my baby weight?

Most women lose about two-thirds of the weight they have put on within a month of giving birth but the rest can be difficult to shift post-pregnancy and can cause self-esteem and confidence issues. It's often harder to lose the weight if you're a slightly older mum, too.

Some women find it easier to lose weight once they stop breastfeeding. Try to lay off the empty calories and just be sensible in your approach to food. Exercise will help you shift any remaining baby weight, but do wait until you've had the all-clear at your six-week check-up before getting started.

Speak to other mums at your stage of pregnancy on the Mumsnet Talk boards.