3D Sonogram


The number of 3d sonogram scans that a woman should have during pregnancy is not set in stone.

A scan is required when a medical professional suspects an abnormality. Otherwise a scan is usually booked for about 7 weeks to confirm pregnancy, exclude ectopic or molar pregnancies, confirm cardiac pulsation and measure the crown-rump length for dating purposes.


A further scan is undertaken at around 18 to 20 weeks. At this time the fetus is big enough for an accurate survey of fetal anatomy and the operator can look for congenital malformations. At this stage it is possible to firmly diagnose multiple pregnancies and assessments dates and growth can also be performed. Placental positioning is also confirmed. Additional scans may be required if abnormalities are suspected.

A large number of centers are now performing an earlier screening scan at around 11-14 weeks in order to measure the fetal nuchal translucency and to assess the fetal nasal bone (and more recently, to detect tricuspid regurgitation) to help in the diagnosis of Down Syndrome. A number of centers will do blood test biochemical screening at the same visit.

More 3d sonogram scans may be carried out at around 32 weeks or later to evaluate fetal size (to estimate the fetal weight) and assess fetal growth. Sometimes these additional scans will be done as a follow up on possible abnormalities identified at an earlier scan.

Placental positioning is further confirmed. The most prevalent reason for having more scans in the later part of pregnancy is fetal growth retardation. In this case, fetal doppler scans may also be required.

3D Sonogram Totals

The total number of scans will depend on what has been detected by a previous scan and whether certain abnormalities were suspected that require follow-up assessment.

What is often called a Level II scan merely indicates a "targeted" examination that is carried out when an abnormality is suspected following a previous examination. Professional bodies like the American Institute of Ultrasound in Medicine do not endorse or encourage the use of these terms. Usually, a more "thorough" examination will be performed at a perinatal center or specialized clinic where more expertise and better equipments are available.

We shouldn’t dwell too much on the definitions or guidelines for a level II ultrasound scan. The prenatal sonologist should always attempt to look for and assess any abnormality that may be present in the fetus. It is not useful to be talking about level III or even level IV scans.

It is gradually becoming routine practice that a pregnancy should be scanned with a 3D sonogram at around 18 to 20 weeks.

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