9. Congenital fetal anomalies - prenatal screening and diagnosis
Covers the causes of congenital fetal anomalies (chromosomal, single-gene, multifactorial and teratogenic) and then the difference between screening for risk and diagnosis for a definite answer. It compares combined, quadruple and cell-free DNA tests for trisomy 21 in a table, and sets out structural screening by ultrasound and serum AFP. A second table gives miscarriage risks for chorionic villus sampling, amniocentesis and cordocentesis, followed by the samples and laboratory tests used.
Topic 9 of 61 in the MU Sofia syllabus for Obstetrics and Gynecology (Medicine, Year 5). The free AceMed note covers it in 5 sections, about 189 words (2 min of reading), with 15 flashcards.
In this note
Introduction
Causes
Screening for chromosomal anomalies
Screening for structural anomalies
Prenatal diagnosis
Introduction
Major congenital anomalies affect about 2–3% of births. Prenatal care separates screening (offered to every woman, gives a risk) from diagnosis (offered to the high-risk group, gives a definite answer).
Causes
Chromosomal: trisomy 21 (Down), 18 (Edwards), 13 (Patau), Turner (45,X); risk of trisomies rises with maternal age.
A high-risk result (for example above 1 in 150) is followed by NIPT or by a diagnostic test. A positive NIPT must be confirmed by CVS or amniocentesis before any decision.
Screening for structural anomalies
First-trimester scan: anencephaly, large defects, increased nuchal translucency (also linked with heart defects).
Anomaly scan at 18–22 weeks: the main screen for structural defects (spina bifida, heart, kidneys, limbs, abdominal wall).
Raised maternal serum AFP suggests an open neural tube or abdominal wall defect.
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