Early Ultrasound (Dating/Viability)

A Dating scan is an ultrasound examination which is performed in order to establish the gestational age of the pregnancy.

Dating scans also reveal other important information such as:

  • The number of fetuses, gestation sacs and placentas.

  • The presence of a heart beat.

  • The size of the fetus, from which the gestational age is estimated.

  • Features of the uterus and maternal structures.

What is a Dating Scan?

Sometimes called a Viability Scan or Dating Scan this may be the first pregnancy scan you will have. It may also be useful for women who do not know the date of their last menstrual period.

This is an Ultrasound examination that is usually carried out vaginally but can be done abdominally. Ideally this scan is performed at around 6 and a half to 7 weeks onwards. It aims to determine the number of fetuses present and whether the pregnancy is progressing normally inside the uterus.

This scan is also useful for women who are experiencing pain or bleeding in the pregnancy and those who have had previous miscarriages or ectopic pregnancies.

What can be seen?

At around 5 ½ weeks gestation, you may be able to see a tiny sac in the uterus, but don't be surprised if the baby and its heartbeat aren't detectable just yet. The term "5 ½ weeks gestation" refers to the time since the first day of the last menstrual period, which can be about 3 ½ weeks from the actual conception date – a little tricky to grasp, right?

However, as your pregnancy progresses to 6 to 7 weeks gestation, exciting developments take place. Through a transvaginal ultrasound, you can clearly see the developing baby, and even witness its heartbeat at this early stage. The heartbeat typically ranges from 90 to 110 beats per minute under 6 to 7 weeks, and then accelerates to 110 to 200 beats per minute as the baby matures.

FAQs

Do I need a full bladder for the scan?

Most early pregnancy ultrasounds are performed with external and internal/vaginal approaches. If you are okay with having an internal scan we do not need a full bladder.

The small internal vaginal scanner causes less discomfort than a smear test examination. It almost always gives clearer and more accurate information about early pregnancy development. 

How long does the scan take?

A dating ultrasound typically takes around 15-30 minutes to complete.

Ultrasound due date or LMP due date, which is correct?

The 'expected date of delivery' (EDD or EDC) is typically determined based on your last menstrual period. If the early dating scan establishes an EDD within 5 days of the one calculated from your last menstrual period, then the EDD is derived from the last menstrual period.

However, if the last menstrual period's information is uncertain or unreliable, or if the dating scan indicates a difference of more than 5 days from the last menstrual period's calculation, the EDD from the early dating scan is utilized. It's important to note that even for women with regular 28-day menstrual cycles, ovulation doesn't always occur on day 14 of the cycle. As a result, your due date might vary based on your conception date.