AN81.1-3 | Prenatal Diagnosis — Glossary

Transabdominal aspiration of amniotic fluid under ultrasound guidance at 15-20 weeks; a diagnostic test for chromosomal, genetic, and neural tube defect screening

Aspiration of chorionic villi from the chorion frondosum at 10-13 weeks via transcervical or transabdominal route; provides earlier diagnostic results than amniocentesis

Non-invasive prenatal testing; analysis of cell-free fetal DNA in maternal blood from 10 weeks; >99% sensitivity for trisomy 21 but is a screening test, not diagnostic

Fragments of fetal DNA from apoptotic placental trophoblast cells circulating in maternal blood from 10 weeks; the basis of NIPT

The fluid-filled space at the back of the fetal neck measured on 1st trimester ultrasound; increased NT (>3.5 mm) suggests risk of trisomies and cardiac defects

A fetal protein produced by the yolk sac and liver; elevated in maternal serum in open NTDs; decreased in Down syndrome and trisomy 18

Second-trimester maternal serum screening measuring AFP, hCG, and unconjugated estriol (uE3) for Down syndrome and NTD risk assessment

Triple screen plus inhibin A; improves Down syndrome detection sensitivity compared to the triple test

Fluorescence in situ hybridisation; a rapid technique (48 hours) using fluorescent probes to detect specific chromosomal aneuploidies (13, 18, 21, X, Y)

The complete set of chromosomes arranged by size and banding pattern; requires cell culture (2-3 weeks for amniocytes); the gold standard for chromosomal diagnosis

Chromosomal mosaicism present in placental (chorionic villus) cells but not in the fetus; a source of false-positive CVS results (1-2%)

Genetic analysis of embryo cells during IVF before transfer; PGT-M for monogenic disorders, PGT-A for aneuploidy screening

Percutaneous umbilical blood sampling (PUBS) from the umbilical cord vein at 18+ weeks; provides fetal blood for rapid karyotype and haematological assessment

Pre-Conception and Pre-Natal Diagnostic Techniques Act 1994 (India); prohibits sex determination for sex-selective abortion; regulates prenatal diagnostic centres

Trisomy 21 (47,XX/XY,+21); the most common chromosomal cause of intellectual disability; risk increases with maternal age; triple screen pattern: AFP down, hCG up, uE3 down

Edwards syndrome (47,XX/XY,+18); second most common autosomal trisomy; clenched fist, rocker-bottom feet, VSD; most die within first year

Patau syndrome (47,XX/XY,+13); holoprosencephaly, cleft lip/palate, polydactyly, cardiac defects; most die within first month

A detailed ultrasound at 18-20 weeks surveying fetal anatomy (brain, spine, face, heart, abdomen, limbs, genitalia) to detect structural defects

Specialised ultrasound of the fetal heart at 22-24 weeks to diagnose congenital cardiac defects

The process of helping individuals understand genetic contributions to disease, interpret test results, and make informed reproductive decisions

A haemoglobin disorder common in India (carrier frequency 3-4%); prenatal diagnosis by CVS or amniocentesis with DNA analysis prevents affected births

A drug used in karyotyping to arrest cell division at metaphase by depolymerising spindle microtubules, allowing chromosome visualisation