What is the first trimester?
Trimesters are a helpful way to think about pregnancy. The changes that happen to you and your baby fall into the 3 time periods of pregnancy:
A full-term pregnancy lasts around 9 months. Most people (including your doctors and midwives) will break this time up into 3 ‘trimesters’ of around 3 months each.
Although you are pregnant from the moment of conception — when a 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 when you conceive naturally, you usually won’t know the date of conception.
What happens to my body in the first trimester?
You might experience nausea during the first trimester, but remember that every pregnancy is different. This is often called ‘morning sickness’, although it can occur at any time of day. While you may have food cravings, you might also experience food aversions, or 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. Your uterus will grow and put pressure on your bladder so that you need to urinate (wee) more often.
What happens to my emotions in the first trimester?
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, but it can help to discuss how you feel with you partner or with a close friend. If you very feel down or anxious, speak with your doctor or midwife, as this can be a sign of antenatal depression or anxiety.
What happens to my baby in the first trimester?
Through the first trimester, your baby goes from being a fertilised ovum to a foetus of about 6cm in length at 12 weeks. By the end of the first trimester, your baby’s heart is starting to beat. The brain, stomach and intestines are developing. There are little bumps known as 'limb buds' where arms and legs are starting to grow.
What can I expect from my doctor or midwife?
Your antenatal (pregnancy) health checks might be with your, GP, a midwife or an obstetrician, depending on the choices you make and where you will give birth. During your first antenatal health check, you will usually 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.
Your doctor will usually offer you an ultrasound scan towards the end of the first trimester. You might hear the baby’s heartbeat at this scan. This ultrasound will also show if you are having a multiple birth (for example, twins) and can help work out the baby’s size and due date. It will also 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 preterm labour
- blood tests to check:
- general maternal health and wellbeing checks, including a discussion of concerns you might have about your pregnancy or general health, and a medicines review (including natural or alternative medicines) to check for their safety during pregnancy
What is the first trimester genetic screening test?
Combined first trimester screen
Your doctor will also discuss with you the combined first trimester screen. If you decide have this screening test, it will check if your baby is at an increased risk of having certain genetic conditions. The screening test involves a blood test and an ultrasound.
The blood test checks for 2 different hormones (beta HCG and PAPP-A). The ultrasound measures the thickness in the fluid in the area behind your baby’s neck. This is known as the nuchal translucency. This area may be larger in babies with certain genetic conditions. A computer program then uses these results, together with your age, weight and how many weeks pregnant you are, to calculate the risk of your baby having a genetic condition.
Non-invasive prenatal testing (NIPT)
Another genetic screening test you may choose to do in the first trimester is non-invasive prenatal testing (NIPT). This is a blood test that can be done from 10 weeks of gestation.
During pregnancy, some of your baby’s DNA (genetic material) from the placenta crosses into your blood stream. NIPT analyses this DNA to see if your baby is at increased risk for certain genetic condition.
NIPT is a more accurate screening test than the combined first trimester screen. However, NIPT is not covered by Medicare, so make sure you ask your provider about costs if you are thinking about having it.
How can I stay healthy through the first trimester?
Staying healthy is especially important during pregnancy. If you smoke, or your partner does, 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. Even low-level drinking, especially in the first trimester of pregnancy, can cause long-term problems for your baby.
Try to eat a variety of nutritious foods during pregnancy as this will help meet your baby’s nutritional needs, 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 certain nutrients. Folic acid and iodine supplements are recommended, as it's difficult to get enough of these key nutrients 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 have any discomfort or complications, speak to your doctor or midwife.
When should I seek medical help?
Bleeding or pain in early pregnancy may be caused by:
- implantation bleeding — when the fertilised egg implants into the uterus lining it can cause some cramping pain or light bleeding
- bleeding from the cervix
- miscarriage — when the pregnancy is lost before 20 weeks of pregnancy
- ectopic pregnancy — when the pregnancy takes place somewhere outside the uterus, like in the fallopian tubes
- molar pregnancy — a rare, abnormal development of the placenta
What else should I consider in the first trimester?
Here are some more things to think about in your first trimester of pregnancy:
- 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 come with you to important health checks.
- Are your vaccinations up to date? Immunisation is important, and some vaccines are funded if you’re pregnant under the National Immunisation Program, so you don’t need to pay. Speak to your doctor or midwife 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, let someone in your health team know.
Your pregnancy journey
Follow your pregnancy week-by-week to find out how your baby is growing and what is happening to your body.
Resources and support
For more information about the first trimester of pregnancy, as well as later stages of pregnancy and birth, see the following resources:
- the NSW Health publication Having a baby
- the Royal Women’s Hospital website
- the Queensland Government online resource What to expect during pregnancy
Speak to a maternal child health nurse
Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.
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Last reviewed: May 2023