Dating scan

A dating scan is an ultrasound scan done in the first trimester of pregnancy. Measurements of your baby are taken to estimate how long you have been pregnant and when your baby is due.

A dating scan can also:

• confirm if you are pregnant with one baby or multiple babies
• check that your pregnancy is not ectopic (when the baby grows outside the uterus)
• check that your baby is growing as expected
• check the position of your placenta

A dating scan can provide an accurate estimated due date (or EDD). You may need a dating scan to work out your due date if you:

• have long or irregular menstrual cycles
• don't know when you had your last period
• got pregnant while taking contraception that affected your menstrual cycle

It's important to have an estimated due date because it helps you:

• have the recommended tests at the right time during your pregnancy
• know if your baby is born prematurely
• know if your pregnancy goes past your estimated due date — in this case, you might consider having your labour induced

If you think you may need a dating scan to help estimate when your baby is due, speak to your midwife or doctor.

A dating scan is most often done in the first trimester, usually between 6 and 8 weeks of pregnancy. At this point, most babies of the same gestational age are about the same size.

If your doctor or midwife also recommends you have a nuchal translucency scan, you may be able to have both together. This way you can have both scans at a single ultrasound appointment between 11 and 13 weeks.

Not everyone needs a dating scan. You, your doctor and your midwife can decide together which tests and ultrasounds you will have during pregnancy.

You will be given information about each test so that you can make an informed decision.

A dating scan is usually done by a trained technician called a sonographer. Other health staff may also be trained to perform a dating scan, such as a doctor or midwife.

Sonographers may be male or female. If you are not comfortable with a male sonographer, tell the reception staff before having your scan.

A dating scan is usually done:

• in a radiology clinic
• in an ultrasound clinic
• at a hospital

In early pregnancy, ultrasounds (including dating scans) can be done through your abdomen (tummy) or vagina. Your sonographer will recommend what type of scan you have based on:

• how far along your pregnancy is
• the position of your baby
• your body shape

Abdominal dating scan

An abdominal ultrasound will usually follow these steps:

• The sonographer will apply a gel to your abdomen.
• The sonographer will gently move an ultrasound wand across your abdomen. It shouldn't hurt, but the gel can feel cold.
• The ultrasound wand sends information back to the ultrasound machine which creates images of your uterus.
• The sonographer may ask for a specialist to come into the room and view the images if necessary.

During the scan, the sonographer will measure your baby's length from head to bottom, known as their 'crown-rump length' (CRL). This measurement can help estimate your baby's gestational age and when they are likely to be born.

If your dating scan is done through your abdomen, you should not urinate (wee) before the scan. This makes it easier for the sonographer to see your uterus (womb).

​​​​​​​Transvaginal dating scan

Your sonographer may recommend a transvaginal ultrasound scan to get a clearer picture of your uterus. A transvaginal ultrasound scan is done through your vagina. If you choose to have one, the sonographer will need to gently insert a small, lubricated ultrasound probe into your vagina. The probe may be a little uncomfortable but isn't usually painful.

You do not need to have a full bladder for a transvaginal ultrasound scan.

Before a transvaginal ultrasound scan, your sonographer will explain why this type of scan is recommended and what will happen. You do not have to have the scan if you don't want to, and it will only proceed with your consent.

When you make the appointment ask if you need to drink water so that you have a full bladder.

Wear loose clothes so it's easy to access your tummy for the scan.

Ultrasounds, including dating scans, do not harm you or your baby or increase your risk of miscarriage. No radiation is used during an ultrasound.

Medicare will cover the cost of your dating scan, but there may be out-of-pocket costs depending on where you go for the test.

It's a good idea to ask about fees when you book your appointment.

You can bring your partner, a family member or a friend to your ultrasound appointments. It can be useful for someone else to listen to the information provided so that you can discuss it afterwards.

​​​​​​​Questions for your doctor

Here are some questions you might want to ask your midwife or doctor:

• Why are you suggesting this test?
• What does the scan involve?
• Do I need to do anything differently on the day?
• When will I get the results?
• Who will contact me to give me the results?
• Do I need to do anything to care for myself after the procedure?

More questions to ask your doctor about tests and scans.

Your midwife, doctor, or obstetrician can answer your questions and give you more information about your estimated due date. Ask if they recommend you have a dating scan.

Visit the Inside Radiology page to find out more about ultrasounds during pregnancy.

Languages other than English

You can learn more about pregnancy and birth with factsheets in many languages on the Royal Women's Hospital page.