Pregnancy Weight Gain: How Much Is Healthy?

Medically reviewed content. Last updated: April 2026.

Weight gain is a normal and necessary part of pregnancy. Your body is growing a baby, building a placenta, increasing blood volume, and storing energy for breastfeeding. But how much weight gain is healthy, and when should you be concerned? This guide covers what the evidence says, trimester by trimester.

How much weight should you gain?

There is no single UK guideline for target pregnancy weight gain. NICE does not set specific weight gain targets and advises against routine weighing during pregnancy. However, the internationally recognised guidelines from the Institute of Medicine (IOM, now the National Academy of Medicine) provide a useful framework based on your pre-pregnancy BMI:

• Underweight (BMI below 18.5): 12.5 to 18 kg (approximately 28 to 40 lbs)
• Healthy weight (BMI 18.5 to 24.9): 11.5 to 16 kg (approximately 25 to 35 lbs)
• Overweight (BMI 25 to 29.9): 7 to 11.5 kg (approximately 15 to 25 lbs)
• Obese (BMI 30 or above): 5 to 9 kg (approximately 11 to 20 lbs)

These are ranges, not precise targets. Every pregnancy is different, and your body will gain weight at its own pace.

Where does the weight actually go?

A total weight gain of around 12.5 kg in a healthy-weight pregnancy breaks down roughly as:

• Baby: 3 to 3.5 kg
• Placenta: 0.7 kg
• Amniotic fluid: 0.8 kg
• Increased blood volume: 1.2 kg
• Breast tissue growth: 0.4 kg
• Uterus growth: 0.9 kg
• Extra fluid retention: 1.2 kg
• Fat stores (energy for breastfeeding and recovery): 2.5 to 4 kg

This means the majority of pregnancy weight gain is not body fat. It is your baby, the structures supporting your baby, and the extra blood and fluid your body needs to sustain the pregnancy.

What does weight gain look like trimester by trimester?

First trimester (weeks 1 to 12)

Most people gain very little in the first trimester, typically 0.5 to 2 kg in total. Some people lose weight due to nausea and food aversions, and this is usually not a concern unless it is severe. You do not need any extra calories during this trimester.

Second trimester (weeks 13 to 27)

Weight gain typically picks up to around 0.4 to 0.5 kg per week. You need approximately 340 extra calories per day during this trimester, roughly equivalent to a slice of toast with peanut butter and a banana. The baby is growing steadily, your blood volume is increasing, and the placenta is fully developed.

Third trimester (weeks 28 to 40)

Weight gain continues at a similar pace of around 0.4 to 0.5 kg per week, though it may slow or plateau in the final few weeks. You need approximately 450 extra calories per day. Some fluctuation from week to week is normal and often related to fluid retention.

What if you gain too much?

Gaining more than recommended is associated with some increased risks, including gestational diabetes, pre-eclampsia, a larger baby (which can complicate delivery), and greater difficulty losing the weight after birth. However, pregnancy is not the time to diet or restrict food. If you are concerned about your weight gain, speak to your midwife for personalised advice.

Helpful strategies include:

• Focusing on nutrient-dense foods rather than calorie counting
• Being mindful of portion sizes without being restrictive
• Staying active with gentle exercise such as walking or swimming
• Avoiding the "eating for two" mentality (you need only a modest increase in calories, not double)
• Limiting high-sugar and high-fat snacks while keeping satisfying alternatives available

What if you gain too little?

Gaining less than recommended is associated with a higher risk of having a smaller baby (low birth weight) and, in severe cases, premature birth. If nausea, food aversions, or loss of appetite are making it difficult to eat enough, speak to your midwife. They can offer practical advice, and if needed, refer you to a dietitian.

Small, frequent meals can help. Focus on calorie-dense, nutritious foods such as avocado, nut butters, full-fat yoghurt, cheese, and smoothies.

What about BMI above 30?

If your BMI is 30 or above at your booking appointment, your midwife will discuss this with you. NICE recommends that people with a high BMI receive additional monitoring during pregnancy, including screening for gestational diabetes (glucose tolerance test, usually around 24 to 28 weeks).

You may be referred to a dietitian for support with healthy eating during pregnancy. The focus should be on eating well and staying active rather than losing weight. Even modest improvements in diet and activity can benefit both you and your baby.

It is important that conversations about weight are handled sensitively. Weight stigma in maternity care is a real problem, and you deserve to be treated with respect regardless of your size. If you feel uncomfortable with how weight is being discussed, you have every right to raise this with your care team.

Should you weigh yourself during pregnancy?

NICE advises against routine weighing during pregnancy because it can cause unnecessary anxiety without changing clinical management. If you find that weighing yourself helps you feel in control, there is nothing wrong with occasional check-ins. If it causes stress or disordered eating thoughts, step away from the scales and focus on how you feel instead.

Your midwife measures your bump (symphysis-fundal height) from around 24 weeks as an indicator of how your baby is growing. This is a more meaningful measure of pregnancy progress than the number on the scales.

After pregnancy

Most people lose around half of their pregnancy weight gain within six weeks of birth, with the rest coming off gradually over the following months. Breastfeeding uses extra calories, which can help, but the primary focus after birth should be recovery, rest, and looking after yourself and your baby.

There is no rush to "bounce back." Your body has done something extraordinary, and it deserves patience and kindness as it heals.

Key takeaways

• Weight gain during pregnancy is normal and necessary, with most of it going to your baby, placenta, blood, and fluid rather than body fat
• Recommended weight gain depends on your pre-pregnancy BMI, ranging from 5 to 18 kg
• You do not need extra calories in the first trimester, and only modest increases in the second and third (340 and 450 calories per day respectively)
• Gaining too much or too little both carry risks, but pregnancy is not the time to diet
• NICE advises against routine weighing, so focus on eating well, staying active, and how you feel
• If you have a BMI above 30, you will receive additional monitoring, and the focus should be on healthy habits rather than weight loss
• After birth, most pregnancy weight comes off gradually over several months

Sources

• NHS. Weight management in pregnancy. nhs.uk
• NICE Clinical Guideline CG62. Antenatal care for uncomplicated pregnancies. 2008, updated 2019
• NICE Public Health Guideline PH27. Weight management before, during and after pregnancy. 2010
• Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. 2009
• RCOG. Being overweight in pregnancy and after birth. Patient information. 2023