Screening for birth defects in pregnancy (prenatal screening) is designed to detect the risk of serious defects in the fetus which mostly originate randomly as a “genetic accident” at conception or in the first weeks of pregnancy.
Procedure of prenatal sequential screening
1. First visit of prenatal counseling
- Information regarding the possibility of screening for congenital defects
- Ultrasound confirmation and detection of pregnancy duration
First part of the screening:
- pregnancy week 10 - 11 - the first blood sample is taken from the patient to examine the following values:
- pregnancy-associated plasma protein A (PAPP-A)
- free beta-subunits of human chorionic gonadotropin (FB-hCG)
- pregnancy week 12 - 13 - I. ultrasound examination to determine:
- measurement of nuchal translucency - NT
- detection of nasal bone (NB) presence of the fetus
- other fetal features (such as blood flow in the vessels of the mother and fetus)
Results of the first part of screening:
The risk of malformation of the fetus is estimated from the combined results of blood tests and first part of the ultrasound screening.
Mothers with significant risk are sent for consultation to the center of prenatal diagnosis where the physician recommends them adequate course of future treatment (e.g. further blood tests to examine free DNA, chorionic villus sampling or amniocentesis).
Second part of the screening:
- pregnancy week 14 to 17 - second blood sample is taken from the patient to examine the following values:
- alpha-fetoprotein (AFP)
- chorionic gonadotropin (T-hCG)
- unconjugated estriol (uE3) - in the event that the results of the first part of the screening were negative
Results of the second part of screening:
To calculate the risk of congenital birth defects of the fetus we use (integrate) the results of the first and second part of the screening. Mothers with a significant risk are sent to the center of prenatal diagnosis for genetic consultation.
- pregnancy week 20
- screening is completed with a detailed ultrasound examination with respect to the progress of the pregnancy so far
- examination of fetal morphology
- examination of fetal heart
Prenatal examination in pregnant women over 35 years and men over 45 years
Risk of certain genetic defects in offspring increases with rising age of the parents. For this reason, age limit of 35 years for women and 45 years for men was determined in the past for recommendation of genetic examinations of the fetus (amniocentesis, chorionic villus sampling). The age of the parents is rather a reason for recommendation of a genetic consultation during which the parents opt for the most suitable procedure of monitoring of fetal development given the current possibilities of indirect prenatal screening (ultrasound, blood tests).