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Losing weight in your first trimester? Here's why

Medically reviewed October 2021

Short on time? Then the key things to know are:

  • It's common for some women to lose weight (up to 2-3 pounds) during the first trimester due to morning sickness, nausea or through adopting a healthier lifestyle
  • Small unintentional weight loss in early pregnancy will not cause any harm to your baby
  • Significant weight loss (more than 5-10% of your body weight) after the first trimester needs to be assessed by your midwife or GP
  • Maintaining a sensible, balanced diet, drinking plenty of water and keeping active during pregnancy is the best way to stay healthy during this time of significant physical and psychological changes to your body


The first trimester of pregnancy can be both incredibly exciting and overwhelming, so when something unexpected occurs it can cause a lot of anxiety, especially when combined with first-trimester exhaustion!

It is common to think that once you are pregnant you will immediately start blossoming on your journey towards your final pregnant shape and bump. So, it seems reasonable to expect to see some weight gain from the beginning of your pregnancy journey, but how much weight gain in the first trimester is ‘normal’?

Well, by the end of the first trimester, most women will notice about 0.5 - 2kg weight gain. However, each pregnancy is a unique journey, and it can be normal for some women to actually lose weight during the first trimester of pregnancy and this is not necessarily a cause for alarm.

Why am I losing weight during pregnancy?

There are two main reasons why women may lose weight while pregnant during the first trimester: morning sickness and nausea which reduces your appetite, or through adopting healthier eating habits.

Get pregnancy advice and support online

Losing weight due to morning sickness

Firstly, many women experience morning sickness around weeks 6-12 of pregnancy. Even if you are not actually vomiting, the experience of nausea can result in you consuming fewer calories each day due to feeling so unwell and being unable to face eating or drinking much.

Losing a small amount of weight due to morning sickness and the associated vomiting or nausea is common and will not cause your baby any harm. Remember, by 12 weeks your baby is only about 5cm in length, so the number of calories and nutritional elements needed are very small at this stage (although vitally important).

However, if you lose more than 5-10% of your body weight, this is significant and more serious causes, such as Hyperemesis gravidarum (excessive nausea and vomiting that often requires hospital treatment), may need further assessment and treatment. If you notice this level of weight loss, it is important to consult your doctor or midwife for assessment.

To work out what percentage of weight you have lost you can use the following simple calculation: simply divide the amount of weight you have lost (in kg) by your starting weight (in kg) and multiply the answer by 100. Find out more about morning sickness in pregnancy.

Why am I losing weight during pregnancy without morning sickness?

The second reason that some women may lose weight during the first trimester is due to a healthier diet and lifestyle. Many expectant mothers consciously make healthier choices when it comes to diet and exercise when they discover they are pregnant. Therefore, their overall calorie intake is often lower than the calories they are burning during exercise and growing their baby.

While it is healthy for mother and baby to make these healthier lifestyle choices, when it comes to exercise and nutrition, it is important to remember that your body is growing a new life and you may need to add some extra healthy snacks into your daily intake as the pregnancy progresses.

Can you lose weight while pregnant?

Although choosing a healthy diet and taking regular exercise is sensible during pregnancy, it is important to remember that it is not advisable to actively diet with the aim of losing weight at this time. Your baby’s growth and development depend upon adequate energy and nutrition from your diet. Actively dieting during pregnancy can result in complications for the pregnancy and your baby such as being born prematurely.

If you notice you are losing weight unintentionally after the first trimester, it is important to discuss this with your midwife or doctor. Weight loss at these stages of pregnancy may indicate problems related to the pregnancy itself or other health conditions. Health conditions that may cause weight loss include diabetes and an overactive thyroid among other problems which need to be investigated further by your GP.

Staying healthy during pregnancy

Unfortunately, the concept of ‘eating for two’ is not accurate. During the first and second trimesters you do not need to increase your calorie intake, so keeping to a daily intake of around 2,000 calories is appropriate for a woman with an average weight and build.

When you reach the third trimester it is recommended that you increase your daily intake by about 200 calories to meet the needs of both your body preparing for delivery and breastfeeding and your baby’s continued growth and development.

It can often be confusing keeping up with advice from different sources about different aspects of being pregnant, but if you follow the simple suggestions below then you will be giving your baby a great start with their growth and development while keeping yourself healthy.

How to stay healthy during your pregnancy:

  • Maintain a balanced diet that includes plenty of fruit, vegetables and lean protein
  • Remember to take a folic acid supplement for the first trimester
  • Keep yourself well-hydrated every day, avoiding too much caffeine or sugary drinks
  • Keep active, regular exercise such as walking or swimming during pregnancy has physical and mental benefits for mum and reduces the risk of complications in pregnancy


In summary, it's not uncommon to lose weight during your first trimester, most often due to morning sickness. However if you lose more than a few pounds, or suffer from extreme sickness, it's best to talk to a GP or midwife. Get more advice from our team of experts at Naytal including the best foods to eat to avoid constipation during pregnancy and the best remedies for dry nipples.

If you have any concerns about your weight during the course of your pregnancy our midwives can help give you advice on what might be going on and what to do next. Book a consultation for one-to-one guidance today.

Dr Alice Wood, Naytal Medical Advisor

Dr Alice is an experienced GP with a special interest in Women's health and emerging health technologies.

First trimester
Pregnancy symptoms
Diet and nutrition