
What is an early pregnancy dating ultrasound?
A dating scan is an ultrasound done within the first 12 weeks of your pregnancy. The purpose of a pregnancy dating scan is to establish how far along you are in your pregnancy. In early pregnancy, babies around the same gestational age typically have very similar measurements. Therefore, an ultrasound done at this time is able to help give a more accurate estimated due date than the date of your last menstrual period alone.
Do I need a dating scan?
In some areas, these early ultrasound scans are offered routinely. However, a lot of the time, the 12 week scan will be the first ultrasound that a pregnant Mama has.
If you are unsure of dates, if you have irregular or long cycles, or if you have a medical condition/history that may indicate a more accurate due date needs to be established, then your provider may recommend an early ultrasound.
When is a dating scan usually done?
Dating scans are always done before 12 weeks. The optimum time is 8-12 weeks gestation, but it can be done a little earlier. What can be seen varies from week to week. At 5 weeks, a gestational sac can often be seen, and at 5.5-6 weeks, a heartbeat can often be detected.
What will happen during my first trimester dating scan?
Depending on your gestation, and what can be visualised, a dating scan often involves a transvaginal ultrasound. This is when the ultrasound probe is inserted into your vagina to allow for a closer and more detailed view of what’s going on in your uterus. This can be a little uncomfortable, but shouldn’t be painful.
When the sonographer is looking at your baby, they will take several measurements, including the crown-rump-length (CRL). They’ll also look for a heartbeat, and assess that any development is appropriate for your baby’s gestation. Following your dating scan, your Dr will be able to determine a more accurate due date for your little one.



Pregnant Mamas once you are in your second trimester make sure you check out our FREE Prenatal class that 8 out of 10 new mothers say they wish they took before birth to ease their stress and worries. You can even watch it at your own pace from the comforts of your own home! Sign up here!
It’s important to note that ultrasounds should be discussed with a healthcare provider to ensure safety and suitability for individual circumstances. This blog is general education only. For any personal based advice regarding you or your baby please seek advice from your own healthcare professional.
- American Pregnancy Association. (2022). Ultrasound: Sonogram. American Pregnancy Association. https://americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/ultrasound/
- Butt, K., & Lim, K. (2019). Guideline No. 388-Determination of Gestational Age by Ultrasound. Journal of Obstetrics and Gynaecology Canada, 41(10), 1497–1507. https://doi.org/10.1016/j.jogc.2019.04.010
- Lj, S., Alfirevic, Z., Cm, B., Ge, C., Ghi, T., Kagan, K. O., Tk, L., Papageorghiou, A. T., Nj, R., Stirnemann, J., Suresh, S., Tabor, A., Timor-Tritsch, I. E., A, T., & Yeo, G. (2012). ISUOG Practice Guidelines: performance of first‐trimester fetal ultrasound scan. Ultrasound in Obstetrics & Gynecology, 41(1), 102–113. https://doi.org/10.1002/uog.12342
- NHS. (2022, September 16). Ultrasound scans in pregnancy. nhs.uk. https://www.nhs.uk/pregnancy/your-pregnancy-care/ultrasound-scans/
- Methods for estimating the due date. (2017). ACOG. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date
- Morgan JA, Cooper DB. Pregnancy Dating. [Updated 2022 Sep 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK442018/