How does screening differ from regular ultrasound?
The screening study is carried out according to a standardized protocol: the doctor is required to obtain and document a certain set of sections and measurements - from a four-chamber section of the heart to sections of the brain and spine. This formalized approach reduces the likelihood of missing a developmental defect, which is the main goal of screening. The timing of 16–22 weeks was not chosen by chance: the anatomy is already distinguishable, and if a severe pathology is detected, the family has time to make decisions and plan the management of the pregnancy. Additionally, markers of chromosomal abnormalities in the second trimester and the condition of the placenta are assessed.
Why are timing screenings needed?
It is no coincidence that ultrasound examinations during pregnancy are carried out at certain times: each window shows its own signs. At 11–14 weeks, the thickness of the nuchal translucency and nasal bone are assessed - markers of chromosomal abnormalities that later disappear. At 18–22 weeks, the formation of organs allows for a detailed examination of the anatomy of the fetus. In the third trimester, the main things are growth, fetal position, condition of the placenta and blood flow.
Missing the screening window means losing information that cannot be obtained at another time.
What is being assessed
- heart rate, number of fetuses and gestational age
- fetometry - dimensions and compliance with deadlines
- anatomy of organs and identification of malformations
- localization, structure and maturity of the placenta
- amount of amniotic fluid
- blood flow in the arteries of the umbilical cord, uterus and fetal vessels
Security
Ultrasound during pregnancy has been used for more than half a century and is recognized as safe when used for medical reasons. International recommendations advise not to conduct research without indications solely for the sake of photos or videos, and also to limit the duration of exposure - the principle of reasonable sufficiency.