Dating Scan
If you are unsure about your dates and are unable to establish when you fell pregnant, it is likely that you will be offered an ultrasound scan to find out your conception date. This will usually happen at your first antenatal appointment and can be the first time you get to see your baby.
When will I have a dating scan?
Most women will be offered a dating scan at around 10 to 14 weeks of pregnancy, but this all depends on your hospital or antenatal unit.
Scans carried out during the first fourteen weeks of pregnancy are incredibly accurate at establishing this information. If you are very opposed to having an ultrasound scan, you may be offered an internal examination. This can also help to ascertain how pregnant you are. The dating scan is also important if you are planning to have tests for Down's syndrome and/or Spina Bifida, because if these tests are performed at specific weeks of pregnancy they are more accurate.
What happens at an ultrasound scan?
At an early scan you need to drink plenty of water, which enables the sonographer to see as much of the uterus as possible. You lie on your back and the sonographer puts some clear gel on your stomach, which helps the ultrasound transducer’s contact with your skin. Sometimes in early pregnancy an abdominal ultrasound cannot pick up much because your baby is still too small. If this is the case you may have to have a vaginal scan, usually called a transvaginal ultrasonography. A small probe is placed inside your vagina to see a clearer picture of how your baby is growing. The probe does not hurt, but will sometimes feel cold from the gel placed on it.
You should be informed of what the sonographer is doing and you should feel able to ask questions about what you can see. Usually, you are able to keep the picture of the scan, but sometimes you may be asked to donate a small fee for it.
The scan will check your baby's heartbeat and that he is developing normally. The sonographer will be able to see your baby's head, arms and legs and some organs, although checking for abnormalities and growth problems doesn't occur until your 20 week scan.
How accurate is a dating scan?
The length of your pregnancy and therefore your due date is worked out from the first day of your last period. This is because most women know when their last monthly period (or LMP) was rather than being able to pin point the exact day they conceived. The confusion occurs because you wouldn't have conceived until 12-14 days after the start of your LMP! The point of the dating scan is to try to reduce the number of women who need labour to be induced because of wrong dates and being overdue. See our Due Date calculator and let gurgle work our when your baby is due.
How big will my baby be at this scan?
As this is probably your first scan your baby will seem very small, in fact it will look like a blob jumping around on the screen and a heartbeat. At this stage your baby will be very small and will be measured from head to bottom, which is called the Crown Rump Length. This is because when babies are very small their legs are all curled up so it is more accurate to measure them from head to bottom.
At around 10 weeks your baby might measure somewhere around 3cm, at 12 weeks it might measure 5-6cm and at 13 weeks it might measure 7cm. This of course is a rough estimate and even at this early stage the size of your bbaby can differ.
How safe are ultrasound scans?
An ultrasound scan is a procedure which uses high-frequency sound-waves to view the internal organs and images of the human body, by reflecting the solid tissue back onto the a computer screen. It is a non-evasive treatment, which means it doesn’t penetrate the skin or body openings, so doesn’t expose you to any infections. This is why it is ideal for tracking the progress of developing babies, as unlike X-rays, it doesn’t expose you or your baby to any radiation.
Can a dating scan show up if I am having twins or not?
The ultrasound can show whether you are carrying twins or multiples as early as your 12 week scan. The sonographer can even identify whether you are carrying identical or fraternal twins by measuring the thickness of the membranes which separate the two amniotic sacs in your uterus. At 12 weeks it’s too early to tell what sex your babies are.
To see what happens at later scans see Antenatal Scans for more information.
Visit our Early Pregnancy area for all your pregnancy queries answered.
Last Modified:
Mothercare
ELC
