Key window 11–14 weeks
Early studies (5-8 weeks) answer basic questions: is the pregnancy uterine or ectopic, is there a heartbeat, how many fetuses are there, is the pregnancy due. The main study of the first trimester is carried out at 11–14 weeks - in this window the thickness of the nuchal translucency is measured and the nasal bone is assessed, the most important ultrasound markers of chromosomal abnormalities. Together with a biochemical blood test, they form a combined screening and allow you to calculate the individual risk of Down syndrome and other chromosomal pathologies. After 14 weeks, these markers disappear and such an assessment can no longer be carried out.
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.