ad. 4. Why is it so important to undergo an anatomical examination before 20 weeks of gestation?
- the ratio of the ultrasound beam width to the size of the fetus is better up to 20 weeks, this allows to apply a wider range of the transducer clearance angles and thereby to reduce the time of an examination.
- up to 20 weeks the assessment of the markers for genetic disorders is most sensitive in the second trimester; in that case, beside the assessment of the anatomy of organs it is possible to perform their assessment reliably;
- in questionable cases this gives time to carry out amniocentesis to identify full karyotype before 22 weeks. It allows to plan the further course of the pregnancy.