First trimester: weeks 1 to 12

First trimester: key stages

The first trimester begins on the first day of your last period and lasts until the end of week 12. This means that by the time you know for sure you're pregnant, you might already be five or six weeks pregnant!

A lot happens during these first three months. The fertilised egg rapidly divides into layers of cells and implants in the wall of your womb where it carries on growing. These layers of cells become an embryo, which is what the baby is called at this stage.

During this trimester, your baby grows faster than at any other time. By six weeks, a heartbeat can usually be heard and by the end of week 12, your baby's bones, muscles and all the organs of the body have formed. At this point, your baby looks like a tiny human being and is now called a fetus. He or she will even be practising swallowing!

Lifestyle changes in the first trimester of pregnancy

You may need to make some lifestyle changes now that you are pregnant. Find out which foods and medicines you should avoid to keep your baby safe and healthy. You’ll also need to cut out alcohol and smoking, and reduce your caffeine intake.

You might be surprised to learn that caffeine is not just found in coffee, but also in tea, chocolate and energy drinks! Find out how much caffeine is in your daily diet.

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Try not to worry if you smoked or drank alcohol before you found out you were pregnant. Now that you know, you can take steps to looking after yourself and your baby.

Get help to stop smoking.

We also have lots of useful tips for coping with everyday pregnancy niggles. It’s common for women to experience symptoms such as morning sickness, cramp and indigestion during the first trimester. But try not to worry, these symptoms mean that your baby is growing strong and healthy!

Don't forget that your mental health is just as important as your physical health. It's normal to feel some anxiety and stress but it shouldn't be ongoing. If what you’re feeling isn’t normal for you, talk to your GP or midwife about it. They are there to help. 

Read more about mental wellbeing in pregnancy.