Dating Scans | Antenatal Ultrasound Clinics | Baby Gender Scans

Antenatal Ultrasound Clinic Information Continued.............

Dating Scan (10 -14 weeks)

All women that are expecting a baby will be offered a dating scan at 10-14 weeks of pregnancy.

It is recommended that you have a dating scan before you have a screening test for Down’s Syndrome. This is because having an accurate due date makes the test more reliable. The hormone levels measured in the blood test vary at the different stages of pregnancy so what might be considered normal at 14 weeks is not considered normal at 16 weeks. If the blood tests is taken too early because your dates are wrong you may get a false positive, which is when you are given a higher risk factor when there really is nothing wrong.

The purpose of the dating scan is to work out how far along in the pregnancy you are. Foetal body measurements reflect the gestational age of the foetus. This dating scan is also used to estimate the due date of the pregnancy. The length of a pregnancy is calculated from the first day of your last menstrual period (LMP),even though you don’t conceive until day 14 after your LMP, and later than this if your normal menstrual cycle is longer than 28 days. The LMP is used because most women know when their last period was, but not many know when they actually conceived.

The gestational age of the foetus is particularly relevant in early pregnancy. If you have an irregular cycle or if you have been taking the contraceptive pill, working out the date of your LMP isn’t very accurate method. Therefore it is essential that foetal measurements are taken as early as possible in pregnancy to arrive at a correct dating.

Scans are more accurate than using the LMP and if the scan date differs from your period date then the scan date will be used. The scan date is generally later that the period date so accurate dating has been found to reduce the number of women having induced labours.

What else will the dating scan reveal?

During the dating scan the sonographer will check that your baby has a heartbeat and is developing normally. At this stage of pregnancy some organs can be seen as well as the baby’s hands, limbs, head and feet. However the dating scan will not show these things in as much detail as the 20 week scan.

The dating scan will also establish the number of pregnancies e.g. if you are expecting twins, triplets or more. It is also really useful at this point to determine if the babies share a placenta, this provides you with the opportunity to plan and prepare for the birth and for your medical care.