Everything you need to know about the 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!
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 9 months of pregnancy. Click here to sign up.
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NHS Choices. Your pregnancy week by week http://www.nhs.uk/conditions/pregnancy-and-baby/pages/pregnancy-week-by-week.aspx#close (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 http://publications.nice.org.uk/antenatal-care-cg62
This content is currently being reviewed by our team. Updated information will be coming soon.