Pregnancy weight gain

Weight gain in pregnancy is generally a good sign - it’s your body’s way of keeping you and your baby safe and healthy, as well as preparing for your little one’s arrival. However, it’s possible to experience too much, or too little, pregnancy weight gain, both of which can come with some additional risks.

So, how much weight should you gain in pregnancy? And what steps can you take to stay healthy? If you’ve got questions, we’re here to help answer them.

In truth, there are no fixed ‘rules’ when it comes to weight gain during pregnancy. Every pregnancy is different, and it all depends on the things that vary from person to person. For example, your genetics and how much you weighed before you became pregnant¹.

You can see how your body mass index (BMI) at the very beginning of your pregnancy can affect how much weight you’re expected to gain in Table 1 below.

As a general rule of thumb, most pregnant women gain between 10kg (22lb) and 12.5kg (28lb) over the course of their pregnancy, and most of that weight gain happens after week 20¹.

Table 1: A guide to weight gain during pregnancy²

Pregnancy weight gain is usually less noticeable at the beginning of your pregnancy, and increases through your second and third trimesters. 

Just like the overall amount of weight you’ll gain during your entire pregnancy, how much you’re likely to gain during each trimester depends on your BMI (you can see an easy-to-follow breakdown in Table 2 below).

Generally speaking, pregnant women tend to gain around one kilo in their first trimester and 0.4kg per week in their second and third trimesters.

Table 2: Weight gain by trimester³

Although you should expect to gain weight during pregnancy, it is possible to gain too much. 

It’s important to keep an eye on your pregnancy weight gain, as putting on too much can affect your health and lead to complications such as¹:

• Gestational diabetes or high blood sugar. Gestational diabetes can have unwanted side effects like dry mouth and blurred eyesight. It can also increase the chance of you having a larger baby and of your baby being born prematurely⁴
• Pre-eclampsia or high blood pressure. Pre-eclampsia can cause severe headaches, problems with your vision, vomiting and sudden swelling of your face, hands, feet and ankles⁵. If you experience any of these symptoms, it’s important to seek medical advice. 

While you should try to avoid gaining too much weight, it’s not a good idea to go on a diet or try to lose weight during your pregnancy¹, and it’s important not to compare yourself to others - everybody is different. If you’re concerned about your pregnancy weight gain, have a chat with your GP or midwife, who can offer you more advice about maintaining a healthy weight during your pregnancy and how to follow a delicious and balanced pregnancy diet.

Not putting on enough weight during pregnancy can also lead to potential issues, like the risk of your baby being born prematurely or with a low birth weight¹. However, some women, particularly those who are of a naturally slim build, may not put on much weight at all during pregnancy and will still have perfectly healthy babies¹.

If you have any worries about whether you’re putting on enough weight during your pregnancy, talk to your GP and midwife, who can give you advice.

Throughout your pregnancy, you’ll be offered all sorts of tests, scans and appointments to make sure your pregnancy is progressing nicely and to keep you and your baby safe.

At your first appointment (also called your booking appointment), your midwife will measure your weight and height to work out your body mass index (BMI)⁶. That’s because women with very low or high BMI could be at risk of more complications during pregnancy. Knowing your BMI will help your healthcare team to know whether you’ll need any extra tests or support¹.

For some people, the thought of being weighed during an appointment can bring up a lot of anxiety. Just remember that every test done at your antenatal appointments is to help make sure you and your little one get the very best care. You can always discuss your feelings with your midwife, who will be able to give you some reassurance and support.

During pregnancy, your body undergoes many changes that can lead to weight gain. Some of these changes are fairly obvious, like your growing bump, while others are less so, like increased blood volume.

The changes in your body that can cause weight gain in pregnancy include:

• Your baby! The average newborn weighs between 3kg and 3.5kg (7-8 lb), so a big amount of the weight you gain is down to your little one getting bigger in your womb¹.
• Your growing placenta. The placenta is an additional organ that grows during pregnancy, feeding your baby and removing waste. By the end of your pregnancy, the placenta will weigh around 500g (1.1lb)⁷. 
• Your uterus and amniotic fluid. Your uterus contains around a litre of amniotic fluid, which keeps your baby cushioned and safe. Together, these can weigh up to 2kg (4.4lb)¹. 
• Increased blood volume. Near the end of your pregnancy, the amount of blood carrying oxygen around your body increases and can weigh up to 2kg (4.4lb)¹.
• Stores of fat. As you reach the end of your pregnancy, your body stores more fat (usually around your thighs, bum and waist), which it will use to make breastmilk to feed your new arrival. That extra fat can account for 3kg (6.6lb) of your pregnancy weight gain¹.

Gaining some weight is a completely natural part of a healthy pregnancy, but gaining too much or too little can come with risks for you and your baby.

By staying active and eating a healthy diet, you’ll be in the best possible position to look after yourself and your little one both during pregnancy and after.

You’ve probably heard the classic line ‘eating for two’, which many people use to describe the ideal diet during pregnancy. But what you might not know is that it’s a myth!⁸

For most of your pregnancy, you can just stick to a healthy diet without adding extra calories. You might feel a little hungrier than usual, but starting the day with a nutritious breakfast should stop you from crashing and reaching for snacks that are high in sugar and fat later in the day⁹. In the last three months of your pregnancy, you’ll want to add around 200 extra calories to your diet to help support your baby as their growth steps up⁸.

Eating well throughout pregnancy will help you maintain a healthy weight as your body changes. You can find lots more information about tailoring your diet for a healthy pregnancy, including delicious and nutritious recipe ideas, here.

Different people experience different energy levels during pregnancy. Some feel more tired and naturally want to rest with their feet up, and others feel energised and ready to go. Either way, staying active while you’re pregnant can boost your mood and energy levels while preparing your body for the birth of your baby and helping you maintain a healthy weight ¹⁰.

If you already take part in a regular activity - keep it up (unless it’s a contact sport or scuba diving, in which case you’ll need to find a new way to stay active!). If you didn’t exercise much, or didn’t exercise at all, before pregnancy, now’s a good time to start. You can ease yourself in gradually with a few gentle walks and increase your activity levels from there.

Why not try:

• Taking the stairs instead of the lift
• Joining an exercise class like yoga or spinning
• Some extra vigorous housework or gardening

If you have other young children, some exercise classes allow them to come along and take part with you. This is a great way to spend some time together ahead of your new arrival whilst staying active at the same time.

Whatever form of exercise you choose to stay active during pregnancy, remember to¹⁰:

• Always warm up and cool down to avoid an injury
• Stay hydrated
• Avoid anything too strenuous in hot weather
• Avoid laying on your back for long periods after 16 weeks