O&G · Antenatal care — prenatal diagnosis
Prenatal diagnosis
Also known as Invasive prenatal testing · Chorionic villus sampling · Amniocentesis · Prenatal genetic diagnosis
Exam-exhaustive FRANZCOG fellowship reference on prenatal diagnosis — chorionic villus sampling (10 to 13 weeks) and amniocentesis (15 to 20 weeks) with technique and the modern procedure-related loss risk (about 0.2 to 0.3%), chromosomal microarray versus karyotype with the Wapner incremental yield, the ACMG five-tier variant classification, and counselling for abnormal and uncertain results. Anchored on RCOG Green-top 8 and the Salomon 2019 loss-rate meta-analysis, globally tagged to MRCOG and ABOG.
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Red flags
- Quoting the historic 1% loss figure when modern evidence shows about 0.2 to 0.3% — overstates risk and misinforms consent
- Ordering a karyotype where a chromosomal microarray is indicated (fetal structural anomaly)
- Acting on a CVS result without considering confined placental mosaicism
- Acting on a variant of uncertain significance as if it were pathogenic
- Missing a balanced translocation or triploidy because microarray does not detect them
- Returning a complex abnormal result without clinical genetics involvement
A 38-year-old at 11 weeks has a cell-free DNA result of 1 in 20 for trisomy 21. She is in your clinic asking whether the baby "definitely has it." The cfDNA is a screen; only an invasive test answers her. The fellowship answer on prenatal diagnosis turns on four things: which procedure, what it samples, what the laboratory platform can miss, and how you counsel the result — including the loss rate you quote.[1][7]
Overview and definition
Prenatal diagnosis is the invasive sampling of fetal tissue to give a definitive cytogenetic, molecular or biochemical answer. It is distinct from screening — cfDNA and the combined first-trimester test estimate risk; CVS and amniocentesis give a result. The indications are a high-risk screen, a fetal structural anomaly, a parental balanced translocation, a previous affected pregnancy, or a molecular risk identified by carrier screening.[1][6][7]
References8ShowHide
- [1]Royal College of Obstetricians and Gynaecologists (RCOG) Amniocentesis and Chorionic Villus Sampling: Green-top Guideline No. 8 BJOG, 2010.Source
- [2]Salomon LJ, Sotiriadis A, Wulff CB, et al. Risk of miscarriage following amniocentesis or chorionic villus sampling: systematic review of literature and updated meta-analysis Ultrasound Obstet Gynecol, 2019.PMID 31124209
- [3]Wapner RJ, Martin CL, Levy B, et al. Chromosomal microarray versus karyotyping for prenatal diagnosis N Engl J Med, 2012.PMID 23215555
- [4]Miller DT, Adam MP, Aradhya S, et al. Consensus statement: chromosomal microarray is a first-tier clinical diagnostic test for individuals with developmental disabilities or congenital anomalies Am J Hum Genet, 2010.PMID 20466091
- [5]Richards S, Aziz N, Bale S, et al. Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology Genet Med, 2015.PMID 25741868
- [6]American College of Obstetricians and Gynecologists Practice Bulletin No. 162: Prenatal Diagnostic Testing for Genetic Disorders Obstet Gynecol, 2016.PMID 26938573
- [7]American College of Obstetricians and Gynecologists' Committee on Practice Bulletins—Obstetrics, Committee on Genetics, Society for Maternal-Fetal Medicine Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226 Obstet Gynecol, 2020.PMID 32804883
- [8]Di Mascio D, Khalil A, Rizzo G, et al. Risk of fetal loss following amniocentesis or chorionic villus sampling in twin pregnancy: systematic review and meta-analysis Ultrasound Obstet Gynecol, 2020.PMID 32632979