First trimester: weeks 1 to 12

You're pregnant: congratulations! The first weeks of your pregnancy are a vital time as your body gets busy building a baby. How exciting!

Weeks 1-12 infographic

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!

When am I due?

Find out your due date using our due date calculator!

When will I see a midwife?

Your first midwife appointment (also known as antenatal appointment) is the 'booking' appointment. This usually happens between week 8 and 10 of your pregnancy. Find out how to register with a midwife and when your appointments will be here.

Keeping your baby safe

There are some things that you can do during pregnancy that have an effect on your baby. Find out about them by clicking the link below.

Find the complete list of pregnancy dos and don'ts (and reasons why) here

Not sure whether you are pregnant?

Find out about the symptoms that mean you may be pregnant here.

Your physical and mental health in pregnancy

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. 

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. 

Exercise, such as yoga, has been shown to reduce anxiety and is a great way to stay active during your pregnancy, too.

Read more about mental wellbeing in pregnancy

Read more about diabetes and pregnancy

Read more about pregnancy with a high BMI

Read more about exercise and pregnancy

Read about the symptoms to look out for in pregnancy

Track your baby's development

Sign up to a free pregnancy email from our midwives to track your baby's development and give you reminders of all you need to know through the nine months of pregnancy. Click here to sign up.


Find out more about the first trimester


NHS Choices. Your pregnancy week by week (Page last reviewed: 28/02/2017 Next review due: 28/02/2020)

Macdonald S, Magill-Cuerden J (2012) Mayes’ Midwifery, 14th edition, London, Ballière Tindall

NICE (2008) Antenatal care for uncomplicated pregnancies, NICE Clinical Guidelines 62. National Institute for Health and Care Excellence

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Last reviewed on June 28th, 2018. Next review date June 28th, 2021.

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Please note that these comments are monitored but not answered by Tommy’s. Please call your GP or maternity unit if you have concerns about your health or your baby’s health.
  • By Midwife @Tommys on 2 Aug 2016 - 11:44

    Yes. A positive pregnancy test means that the pregnancy hormone, HCG is present in your urine. This hormone is present once you have conceived. Some pregnancy tests can be taken several days before your period is due – but the earlier you take the test, the less reliable the result. To have a more accurate result, take the test at least a week after your period would have been due

  • By Midwife @Tommys on 2 Aug 2016 - 11:24

    As long as you do not have any history of early miscarriages , or recent episodes of bleeding., intercourse in the first trimester is absolutely fine!

  • By Anonymous (not verified) on 31 Jul 2016 - 10:49

    hi I m pregnet now my first month I wan ask some think during 1 month pregnancy can we do inter sorce

  • By Anonymous (not verified) on 29 Jul 2016 - 18:43

    Hi I last had my period on 11 July and lasted four days but since last week been feeling tired and exhausted so did a pregnancy test came back positive is it possible that I am pregnant before my actual next period came?

  • By Midwife @Tommys on 29 Jul 2016 - 16:22

    Our advice is to take any pregnancy test as a positive, tests do have slightly different sensitivity. I would suggest to wait a week and repeat the test. Or else you can go back to the GP and ask for a blood test which is more sensitive and accurate. In the meantime I would suggest to start taking folic acid and vitamin D supplement if you have not already and be aware of foods to avoid in pregnancy in case you are pregnant.

  • By Anonymous (not verified) on 29 Jul 2016 - 16:12

    I had a positive test at home so i sent a urine sample to the doctors but it came back negative the day i got told it was negative i done another test at home and it was positive again what should i do

  • By Midwife @Tommys on 26 Jul 2016 - 15:34

    The recommended time is the day after you have missed your next period as being the most accurate time , although there are some tests on the market that state they can give an earlier result

  • By Anonymous (not verified) on 26 Jul 2016 - 02:27

    When will it be a good time to test

  • By Anonymous (not verified) on 13 Jul 2016 - 10:45

    Wow, I'll learn a lot from this website.
    Keep it up guys.

  • By Anonymous (not verified) on 5 Jul 2016 - 07:47

    Very informative and nice information indeed

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