When to have dating ultrasound
Your sonographer will be experienced at performing these ultrasounds during pregnancy. It involves scanning with the ultrasound probe lying in the vagina.The transvaginal ultrasound probe is thin, about 2cm diameter.For example, this test will not tell us "no, the baby definitely does not have trisomy 13, 18 or 21" and, this test will not tell us “yes, your baby definitely has trisomy 13, 18 or 21”.To get a definitive 100% answer for chromosome abnormalities including Down syndrome, a prenatal diagnostic test is needed (chorionic villus sampling or amniocentesis).The probe is covered with a disposable protective sheath.A small amount of ultrasound gel is placed on the end of this probe.The thickness of this fluid can be precisely measured and this is called the nuchal translucency (or NT) measurement.
If you have concerns about transvaginal ultrasound, please discuss this with your sonographer.
This means that combined first trimester screening simply tells us if your risk is low or high.
For example, it tells us whether your baby has a low risk of having trisomy 13, 18 or 21, or whether your baby has a high risk of having trisomy 13, 18 or 21.
An increased NT measurement does not always mean the baby has a problem but it does increase the risk.
There are established and strict criteria for the accurate measurement of the nuchal translucency.