What is a dating scan?

A dating scan is an early pregnancy ultrasound used to measure the developing baby and estimate gestational age. It also confirms the baby’s heartbeat, checks for multiple pregnancies, and verifies the pregnancy location in the uterus.

At QUFW, dating scans are performed by our caring, experienced sonographers using high-resolution equipment to ensure accurate measurement and clear images.

This fact sheet answers the following questions:

1. When should I have a dating scan?
2. What happens during a dating scan?
3. How accurate is a dating scan?
4. Do I need a dating scan?
5. What is the difference between a dating scan and the 13 week early anatomy scan?

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1. When should I have a dating scan?

The most accurate time for a dating scan is between 7 and 10 weeks of pregnancy.

• Before 7 weeks: The scan can confirm a gestational sac and yolk sac from 5 weeks, a heartbeat after 6 weeks, but measurements may be less reliable to confirm viability and dating A gestational sac visualised within the uterus confirms correct pregnancy location.
• Between 7 and 10 weeks: The crown–rump length (CRL) measurement is most accurate for establishing your estimated due date (EDD).
• After 10 weeks: Dating is possible, but accuracy decreases as babies start to vary more in size.

Some people have an earlier scan (6–7 weeks) if they have irregular cycles, are unsure of their last menstrual period (LMP), have conceived through IVF, or have a history of pregnancy complications.

8 week fetus with heartbeat

2. What happens during a dating scan?

At QUFW, your sonographer will:

1. Review your referral and confirm your details.
2. Explain the scan process and answer any questions.
3. Perform the scan using either a transabdominal (across the abdomen) or transvaginal (internal) approach, depending on gestational age and image clarity.
4. Measure the CRL, check for heartbeat, number of babies, and other factors such as ovaries. Provide images and send a detailed report to your referring doctor.

Most dating scans take around 15–30 minutes. They are safe, non-invasive, and use no radiation, however we always practice ALARA (As Low As Reasonably Achievable) principles.

3. How accurate is a dating scan?

A dating scan in the first trimester is a reliable way to determine gestational age.

• CRL measurements taken between 7 and 10 weeks are accurate to within ± 5 days.
• Later scans may be less accurate because individual growth patterns vary.

If the scan’s EDD differs from your LMP-based date, your healthcare provider will usually use the ultrasound date.

4. Do I need a dating scan?

You may be advised to have one if:

• You are unsure of your LMP or have irregular cycles.
• You have conceived via assisted reproduction.
• You have a history of early pregnancy loss or ectopic pregnancy.
• Your doctor recommends one for clinical reasons.

5. What is the difference between a dating scan and the 13 week early anatomy scan?

While both are first-trimester ultrasounds, their purposes differ:

Dating scan	Early anatomy scan/First Trimester Combined Screening ultrasound
7–12 weeks	13-13+6 weeks
Measures CRL to determine EDD	Measures CRL to confirm EDD and appropriate growth of baby. Can be used as a dating scan if no prior dating ultrasound has been performed.
Confirms heartbeat, multiples, location of pregnancy	Checks early anatomy structures including a heart beat In the instance of no prior NIPT, it can provide a First trimester risk assessment for chromosomal abnormalities such as Trisomy 21, 18 and 13when combined with First trimester blood tests and measuring the fluid at the back of the baby’s neck (Nuchal Translucency) Can also provide Pre-eclampsia screening

 

FAQs

Is a dating scan safe?

Yes. Ultrasound is considered safe in pregnancy and does not use radiation.

Can my due date change after a dating scan?

Yes. If ultrasound findings differ from LMP-based dates, your healthcare provider may adjust your due date.

Can a dating scan detect twins?

Yes. A dating scan can confirm if you are carrying more than one baby and whether they share the same placenta or have separate placentas which is important for managing your pregnancy moving forward.

Do I need a full bladder for a dating scan?

For an early dating scan, a partially full bladder may help improve image clarity. Your clinic will confirm preparation instructions when booking.

What if the scan doesn’t show a heartbeat?

If it’s too early in pregnancy, the heartbeat may not be visible yet. Your doctor may recommend repeating the scan in one to two weeks.

Can a dating scan show the baby’s gender?

No. It is too early in pregnancy for accurate gender determination.

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