播客摘要
Podcast Summary for S2E3: Navigating the Choices in Prenatal Genetic Testing
Yoyo Chu
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Full episode is available here (in Cantonese).
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From Age-Based Screening to Personalised Risk Assessment
For a long time, prenatal risk assessment relied heavily on a single criterion: the mother’s age. Women aged 35 or above were routinely advised to undergo invasive testing, as statistics show that the risk of chromosomal abnormalities — such as Down syndrome — increases with age.
This approach had clear limitations: older mothers with relatively low individual risk were subjected to unnecessary invasive procedures, while younger mothers with higher personal risk were sometimes missed by the screening net altogether.
Medical practice later evolved to incorporate a more refined assessment combining nuchal translucency ultrasound at 11 to 13 weeks of pregnancy, blood biochemical markers, and maternal age, producing a personalised risk estimate that more accurately reflects each individual’s circumstances.
Over the past decade, the introduction and widespread adoption of Non-Invasive Prenatal Testing (NIPT) has marked yet another significant advancement in prenatal screening.
NIPT: Capabilities and Limitations
NIPT analyses cell-free DNA fragments derived from the placenta that circulate in the mother’s bloodstream, using this information to assess the risk of certain chromosomal conditions in the foetus. Its core value lies in its role as a “triage” tool — more accurately identifying those who genuinely require further diagnostic investigation.
NIPT is a screening test, not a diagnostic test. Its results indicate probability — either high risk or low risk — and cannot provide a definitive conclusion. A confirmed diagnosis still requires invasive testing, such as amniocentesis or chorionic villus sampling (CVS), which directly analyses foetal cells.
NIPT and routine ultrasound serve distinct and complementary purposes: NIPT assesses genetic risk, while ultrasound evaluates the foetus’s structural development, including the heart, brain, spine, and limbs. Neither can replace the other.
The scope of NIPT has expanded considerably in recent years. While traditional NIPT focused on common chromosomal conditions, some tests can now detect certain single-gene disorders, offering families without a known family history an earlier opportunity to identify potential risks.
In Hong Kong, NIPT is currently a self-funded option, representing a family’s active decision to seek more information. Understanding both what NIPT can and cannot tell you is essential to making an informed choice.
Invasive Prenatal Diagnosis: Comparing Amniocentesis and CVS
Invasive prenatal diagnosis may be considered when NIPT results indicate elevated risk, when ultrasound identifies structural anomalies, or when a family has a known hereditary condition.
Chorionic villus sampling (CVS) is typically performed between 11 and 14 weeks of pregnancy. A small sample of placental tissue is collected for laboratory analysis. Its key advantage is the earlier timing, giving families more time to process results and make decisions. However, since the sample is taken from placental tissue rather than directly from foetal cells, results may occasionally require further confirmation.
Amniocentesis is typically performed between 16 and 20 weeks of pregnancy. A fine needle is inserted through the abdominal wall to withdraw a small amount of amniotic fluid containing foetal cells that have naturally shed. It carries a very high degree of diagnostic accuracy and is one of the standard methods for confirming chromosomal abnormalities.
Both procedures carry a similar risk of pregnancy loss, approximately 0.5%, meaning roughly one in every two hundred cases may experience miscarriage or other complications.
The Role of Genetic Counselling: Clarifying the Decision-Making Framework
The role of a genetic counsellor is not to direct a decision, but to help expectant parents fully understand the implications of each option and make a choice that is best suited to their own circumstances and values.
When considering whether to proceed with invasive prenatal diagnosis, the counselling process typically explores three key dimensions:
First, whether the family is emotionally prepared to receive a serious diagnosis, including whether termination of pregnancy would be considered under certain circumstances;
Second, whether viable treatment options — either during pregnancy or after birth — exist for the condition in question;
Third, the family’s psychological capacity to accept the 0.5% risk of pregnancy loss associated with the procedure.
These three dimensions involve deeply personal considerations, including individual values, religious beliefs, and family support systems. There are no standard answers, and no choice is inherently “right” or “wrong.”
Conclusion
Prenatal genetic testing is not a straightforward yes-or-no decision, but rather a deeply personal conversation centred on a family’s individual needs and circumstances.
NIPT, amniocentesis, and CVS are tools designed for different stages of the prenatal journey. What matters most is not which test is chosen, but why it is chosen — and whether the family is adequately prepared for the range of possible outcomes.
Next episode: Thalassaemia carriers — it’s not as simple as just being “anaemic.”
GENE TALKS Podcast Disclaimer
The content of this podcast is provided for general educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment of any kind.
If you have questions about your personal health, genetic test results, or medical decisions, you should consult a qualified healthcare or genetics professional.
Any cases, experiences, or opinions mentioned in this program reflect the personal views of the host, and do not represent the positions of any medical institutions or professional organisations.
While GENE TALKS and its host endeavor to provide accurate and reliable information, they are not responsible for any consequences arising from the use or interpretation of the content.
Our mission: to help you understand genetics — and yourself — not to replace professional judgment.