Prenatal screening – Structural Echoscopic Examination (SEO)

Second trimester 

Between 19 and 21 weeks of pregnancy, you will be ready for the structural echoscopic examination (SEO). 

The 20 weeks’ ultrasound is also called the structural echosopic examination. The main purpose of this test is to find out whether the baby may be having a split spine or anencephaly. We study in detail how the baby’s organs are developing and we are able to see if any other physical abnormalities might be present (see examples below). Also, we decide on whether the child is growing properly and whether sufficient amniotic fluids exist. 

Abnormalities that may be seen during the 20 weeks’ ultrasound include a split spine, anencephaly, hydrocephalus, cardiac abnormality, fracture or hole in the diaphragm, fracture or hole in the abdominal wall, lack of or abnormal kidneys, lack of or abnormal bones, lack of or abnormal arms or legs. Even If abnormalities do not present themselves during the 20 weeks’ ultrasound, this does not mean a perfectly healthy baby should be taken for granted. Not every abnormality can be seen during the ultrasound.

If you need more information about this test you may contact your obstetrician or read the RIVM leaflet.

Informatie over de 20 weken echo engels    Download here the RIVM leaflet on the structural echoscopic examination.



A negative ultrasound and/or screening outcome usually means a troubled pregnancy. To diagnose matters properly, a follow-up test in recommended in most cases. 

The follow-up test involves a so-called corionic villus sampling (between 11 and 14 weeks of pregnancy) or an amniocentesis (after 15 weeks of the pregnancy). 

Sometimes a detailed ultrasound is performed. This follow-up test is also referred to as the prenatal examination. 

Depending on the nature and seriousness of the abnormality at hand, this test will be performed in the second or third line (at the regional or academic hospital). 

The ultrasound operator will answer all your questions about the results and schedule a follow-up test (if necessary) or an appointment with your obstetrician and/or gynaecologist.