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First three months pregnancy


Everything you need to know about the first trimester (weeks 1 to 12)

Tommy's PregnancyHub

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

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!

Try our Healthy Pregnancy Tool to find out everything you need to know about your pregnancy

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.

Review dates

Reviewed: 28 June 2018

Next review: 28 June 2021


This content is currently being reviewed by our team. Updated information will be coming soon.

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First trimester | Pregnancy Birth and Baby

First trimester | Pregnancy Birth and Baby beginning of content

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From the moment you get the news that you are pregnant, you will probably be filled with a rush of emotions – and most likely a flood of questions too. While the first trimester of pregnancy is filled with a host of changes for you and for your baby, many will be invisible to the outside world. Read on to find out what happens to your body and how to stay healthy.

What is the first trimester?

A full-term pregnancy lasts around 9 months, and most people (including your doctors and midwives) will break this up into 3 ‘trimesters’. Although you are pregnant from the moment of conception – when a male sperm fertilises your ovum (egg) – the first trimester of pregnancy is counted from the first day of your last period through to week 12. This is because most women who conceive naturally won’t know the date of conception.

Trimesters are a helpful way to think about pregnancy because the changes that happen to you and your baby fall into the 3 broad categories of early, middle and late pregnancy, called first, second and third trimesters.

What happens to your body?

For some women, the first trimester is characterised by nausea (often called ‘morning sickness’, although it can occur at any time of day). But remember that every pregnancy is different and while some women have food cravings, others experience food aversions, and some have no change in appetite at all.

Other changes in the first trimester include changes to your breasts as they become tender, larger and heavier, while your uterus will grow and put pressure on your bladder so that you need to urinate more often.

Your emotions

You might feel a range of emotions during your first trimester. Hormone changes may make you feel moody or irritable, and tiredness is common in the early months. These feelings are normal, so discuss how you feel with you partner or with a close friend. If you feel down or anxious, speak with your doctor or midwife.

What happens to the baby?

Through the first trimester, your baby goes from being a fertilised ovum to a fetus of about 6cm in length at 12 weeks. By the end of the first trimester, your baby’s heart is starting to beat, and the brain, stomach and intestines are developing. There are little bumps known as 'buds' where arms and legs are starting to grow.

What can be expected from the doctor and midwife?

Your antenatal (pregnancy) health checks might be with your GP, a midwife or an obstetrician, depending on where you will give birth. During your first antenatal health check, you will probably have your pregnancy confirmed with a urine or blood test. These are more reliable than home pregnancy tests. First trimester antenatal health checks usually happen every 4 to 6 weeks, but this can vary, based on your health and how your baby develops.

Many women are offered an ultrasound scan at around 12 weeks – you might hear the baby’s heartbeat at this scan. This ultrasound will also show if you are having a multiple birth (e.g. twins) and can help estimate the baby’s size and due date, as well as check for some health conditions.

Other health checks during the first trimester include:

  • urine tests to detect urinary infections, a common but manageable condition that if left untreated can trigger pre-term labour
  • blood tests to check your blood type (particularly Rh status), iron levels, blood sugars (for gestational diabetes), rubella (German measles) immunity, and other infections such as HIV, hepatitis B and syphilis
  • general maternal health and wellbeing checks, including a discussion of concerns you might have about your pregnancy or general health, and a medication review (including natural or alternative medicines) to check for safety during pregnancy

How to stay healthy

Staying healthy is doubly important during pregnancy. If you are a smoker, this is a great time to quit – speak with your doctor or pharmacist for support.

It is safest not to drink any alcohol while you are pregnant, since even low-level drinking, particularly in the first trimester of pregnancy, can have long-term negative effects on your baby.

Try to eat a variety of nutritious foods during pregnancy since this will help meet your baby’s nutritional requirements, as well as your own. While the amount of food you need to eat during your first trimester won’t increase by much, you will need more of some nutrients. Most women will also need folic acid and iodine supplements because it's difficult to get enough of these from food alone.

It’s important to keep up regular physical activity during your pregnancy because of the many benefits both for you and your baby. If you experience any discomfort or complications, speak to your doctor or midwife.

Things to consider in the first trimester

  • Book your antenatal appointments for the whole trimester – they are important for tracking your health and your baby’s growth.
  • Get support – ask your partner, a friend or a family member to go with you to health checks.
  • Are your vaccinations up to date? Immunisation is important, and several vaccines are funded for pregnant women under the National Immunisation Program. Speak to your doctor for guidance.
  • Your doctor or midwife can help you access a range of support services, not just for medical concerns - for example, if you feel you are at risk of violence or you are feeling vulnerable during your pregnancy.

Your pregnancy journey

Follow your pregnancy week-by-week to find out how your baby is growing and what is happening to your body.

Sources:
NSW Health (Having a baby), Royal Women's Hospital (Pregnancy and birth), Raising Children Network (Pregnancy week-by-week), Women's and Children's Health Network (The first 3 months of pregnancy: the first trimester), Better Health Channel (Pregnancy - prenatal tests)

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: May 2021


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Related pages

  • Second trimester
  • Third trimester
  • Pregnancy week-by-week

Need more information?

Pregnancy at week 7

Your baby is now about 1cm long and if you haven’t seen your doctor yet, now is a good time to start your antenatal care.