Weight gain in pregnancy

How much weight will I gain during pregnancy?

By the end of pregnancy you may weigh 10kg to 12.5kg more than you did before you were pregnant (NHS 2015).

This varies from person to person, so check out our pregnancy weight gain estimator to get a more personal figure based on your own height and pre-pregnancy weight.

It's natural and healthy to put on weight during pregnancy. Your body needs to change to help you grow your baby, and to give her the best start in life.

By the time you reach your due date, just over a third of your extra weight will come from your baby, the placenta and amniotic fluid (Murray and Hassall 2014).

Every mum and baby is different, but here are some averages:

• At birth, a baby weighs about 3.3kg.
• The placenta, which keeps your baby nourished, weighs about 0.7kg.
• The amniotic fluid, which supports and cushions your baby, weighs about 0.8kg.

The other two-thirds of extra weight is due to the changes that happen to your body while you’re pregnant. On average:

• The muscle layer of your uterus (womb) grows dramatically, and weighs an extra 0.9kg.
• Your blood volume increases, and weighs an extra 1.2kg.
• You have extra fluid in your body weighing about 1.2kg.
• Your breasts weigh an extra 0.4kg.
• You store fat, about 4kg, to give you energy for breastfeeding.
  (Murray and Hassall 2014)

What is my body mass index, and how will it change during pregnancy?

Your body mass index (BMI) is a measure of your weight in relation to your height. It’s an accurate way of telling whether or not your weight is in the healthy range.

The amount of weight you should put on in pregnancy depends on what your BMI was before you were pregnant.

Your midwife or doctor will probably calculate your BMI at your first appointment (DH 2018, RANZCOG 2017). You can also work out your BMI using our BMI calculator.

The Department of Health’s guidelines for healthy weight gain during pregnancy give these ranges (DH 2018):

Pre-pregnancy BMI	BMI	Total weight gain
Underweight	Less than 18.5	12.5kg to 18kg
Healthy weight	18.5 to 24.9	11.5kg to 16kg
Overweight	25 to 29.9	7kg to 11.5kg
Obese	30 or more	5kg to 9kg

You’ll gain most of this weight after 20 weeks (NHS 2015).

If you’re pregnant with twins, you’d expect to gain more (IOM 2009):

Pre-pregnancy BMI	BMI	Total weight gain
Healthy weight	18.5 to 24.9	16.5kg to 24.5kg
Overweight	25 to 29.9	14kg to 23kg
Obese	30 or more	11kg to 19kg

If you’re expecting triplets or more, talk to your doctor about healthy weight gain for you.

Will I be weighed while I'm pregnant?

Your midwife or doctor will probably weigh you at your first or booking appointment (DH 2018, RANZCOG 2017). He'll then work out your BMI (NICE 2010).

Your caregiver may weigh you at every antenatal appointment, or not again until your third trimester (DH 2018). Putting on more weight than you expected may affect your plan for labour.

Your caregiver will measure the size of your bump regularly throughout your pregnancy to check how well your baby is growing.

If your baby seems large, you’re unlikely to have extra ultrasound scans, as long as your pregnancy is healthy. But if your baby is very small, your doctor or midwife will suggest you have a scan (NCCWCH 2008) to better check your baby’s growth.

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

If you had a BMI of 30 or more before you conceived, ask what extra support you may be able to receive. Your doctor or midwife may refer you to a dietitian or obstetrician. They will give you personalised advice on eating healthily and the best sort of exercise to do. This will help you control how much weight you gain.

Carrying a lot of extra weight at the start of pregnancy can increase your risk of complications during your pregnancy and labour, and make you more likely to have:

• high blood pressure or pre-eclampsia
• gestational diabetes
• a big baby (macrosomia) or a baby with low birth weight
• a caesarean
• a premature labour and birth
  (RANZCOG 2017)

Sadly, having a BMI of 30 or higher is also linked to a higher risk of stillbirth (Scott-Pillai et al 2013). The risk is still low, though.

But don’t be tempted to go on a diet while you’re pregnant. Low-kilojoule or crash diets may make you unwell and could affect your baby (NICE 2010).

Instead, aim to eat healthily and be active. Being healthy will make your pregnancy and your labour easier. It will also help you return to a healthy weight after you’ve had your baby (NHS 2017a).

Swap unhealthy foods for healthier alternatives. Instead of biscuits, cakes, lollies and ice cream, which are high in saturated fat and sugar, choose fresh fruit and veggie sticks, wholegrain crackers and low-fat cheese, yoghurt or a handful of nuts and some dried fruit.

Swap fizzy drinks for diet versions, or even better, water. Just simple changes such as these will really make a difference.

You could join a pregnancy exercise class, such as antenatal yoga, Pilates or aquanatal. They’re a great way to meet other mums-to-be and keep up your motivation to exercise.

Try to build extra movement into your day. For example, take the stairs instead of the lift, go on short walks, or get off the bus a stop early.

Ask your midwife or doctor for ideas about how to eat well and be more active.

What should I do if I'm underweight and pregnant?

Speak to your midwife or doctor about how to build yourself up gradually over the coming months. Follow his advice to eat a variety of healthy, nutritious foods, so you and your baby will get the kilojoules and essential vitamins and nutrients you both need.

You'll be doing the best for your baby if you keep up your weight gain. You may be more likely to have anaemia, a premature or low-birth weight baby if your BMI is low (Denison et al 2014, Scott-Pillai et al 2013). Babies who are born early and small sometimes need extra care when they’re born.

What if I'm diabetic and pregnant?

If you have diabetes, it's especially important to start your pregnancy with a healthy BMI. If you're not yet pregnant, see your GP to have a look at what you’re eating. She'll help you monitor your blood sugar levels (NCCWCH 2015) and make sure you have the right dose of folic acid (NICE 2016).

If you’re already pregnant, you’ll need to keep your blood sugar levels stable. Ask your doctor for advice on the best possible diet to keep you and your baby healthy (NCCWCH 2015). Most major maternity hospitals have a special team of doctors, midwives and nurses who are trained to look after mums-to-be with diabetes (NICE 2016).

How can I control my weight during pregnancy?

The best way to stay in control of your weight is to eat a healthy, balanced diet and keep active.

You don't need to eat for two, but you do need extra kilojoules during your second and third trimesters (NHMRC and NZ MH 2006). Those kilojoules should come from healthy food and drinks, though.

To eat healthily, have a variety of the following foods:

• Bread, pasta, potatoes, rice and cereals (carbohydrates). Choose wholegrain varieties, such as brown rice and pasta, and wholemeal bread.
• Lots of different colours of fruit and vegetables, fresh, tinned or frozen. Aim for at least five serves of vegetables and two of fruit a day.
• Proteins, such as meat (but not liver), fish, eggs and legumes.
• Dairy products, such as milk, yoghurt and cheese, or calcium-rich alternatives. Choose low-fat versions if you’re overweight.
  (NHMRC 2013)

Avoid having large meals. You could use a smaller plate if that helps you limit your portion sizes. Eating little and often may also help prevent heartburn or indigestion (NHS 2017c).

Try to make biscuits, cakes and soft drinks an occasional treat (NHMRC 2013, NHS 2017b).

More about weight and healthy eating during pregnancy

• Reasons why exercise is good for your pregnancy
• How to get more fruit and veg in your diet