You usually have one or more ultrasound scans during pregnancy. The two scans usually offered are the nuchal scan and the anatomy scan.
It's not usual to have a dating scan early in your pregnancy to work out how many weeks pregnant you are and your due date. However, you may need a scan in early pregnancy if you have complications such as bleeding.
Sometimes other scans are carried out to check the growth of your baby or the position of your baby or the placenta. You will need extra scans if you’re carrying twins or if you have had complications in this pregnancy or a previous pregnancy.
Nuchal translucency scan
You will be offered this scan at 12–14 weeks' gestation. This scan confirms your pregnancy due date, finds out if you are having twins and looks for abnormalities in your baby. However, your baby is still quite small at this stage (about 5–8cm long) so most abnormalities are better checked for at 20 weeks when your baby is bigger.
The nuchal translucency is the measurement of fluid behind your baby’s neck. This result can be used (along with blood tests) to calculate the chance of your baby being born with some genetic conditions such as Down syndrome. If the scan and blood tests show that your baby has an increased chance of having Down syndrome, you have the option of having further testing such as amniocentesis or NIPT (non-invasive prenatal testing).
Sometimes the sonographer will need to do an internal (transvaginal) ultrasound to get good images of your baby.
You will be offered a scan at around 18–20 weeks’ gestation, which is also called the second trimester scan or morphology scan.
Many important structural problems can be seen with a scan at this stage. This scan is usually the most detailed examination and includes assessment of the development of your baby and the position of the placenta.
Placenta previa (where the placenta is covering your cervix) may be diagnosed during the anatomy scan. However, as your baby develops and your uterus gets bigger, the placenta usually moves away from your cervix. It is usually not possible to know if the placenta has moved far enough for a normal birth until 32 weeks and sometimes even later. You may be offered additional scans later in your pregnancy to check for this.
At this scan, you can usually find out your baby’s sex. However, if your baby is lying in an awkward position their sex can’t be worked out.
A report of the ultrasound findings will be sent to your doctor or midwife. They will discuss the results with you.