Podcast Summary: Dr. Chapa’s OBGYN Clinical Pearls

Episode: cfDNA: Jan 2026 Practice Advisory
Date: January 10, 2026
Host: Dr. Chapa
Topic: New ACOG & SMFM Guidance on Cell-Free DNA (cfDNA) Screening for Fetal Chromosomal Abnormalities

Overview

This high-yield episode reviews the latest 2026 ACOG Practice Advisory on cfDNA for screening fetal chromosomal abnormalities, which updates and supersedes Practice Bulletin 226. Dr. Chapa provides practical pearls for medical students, residents, and clinicians on what has changed—especially regarding screening for sex chromosome abnormalities (SCAs)—and what remains the same. The episode drills into the science, accuracy, counseling, and clinical management implications of these new recommendations, connecting them to SMFM's November 2025 Consult Series 74.

Key Discussion Points & Insights

1. The Fast-Paced Nature of Medicine and New Guidance

• Medicine and science are ever-evolving, and so clinical practices are regularly updated in response to new evidence.

  “Medicine moves fast. Now, the reason medicine moves fast is because science, on which medicine is based, also moves fast.” (00:36)

2. What's Changed: The 2026 ACOG Practice Advisory

• January 2026 saw a new ACOG Practice Advisory on “Screening for Fetal Chromosomal Abnormalities,” replacing Practice Bulletin 226.
  • Driven by new recommendations and data, particularly from SMFM Consult Series 74 (Nov 2025), now endorsed by ACOG.

3. cfDNA Screening: What Remains the Same (10:00–12:30)

• cfDNA is still recommended for trisomies 21, 18, and 13 (Down, Edwards, and Patau syndromes).
• Offerable to all patients (not just high-risk) following proper pre-test counseling.
• cfDNA is approved and accurate for these aneuploidies in both singleton and twin gestations.

  “Trisomy 18, 13, 21 using cell free DNA. Super good. Whether you're multiple or twins…” (12:45)

• Not enough data for higher-order multiples (triplets or more): cfDNA not recommended.
• Still not recommended for microdeletions or large genome-wide copy number variants.

  “Micro deletion screening using cell free DNA is still not recommended.” (07:50, 12:30)

4. Sex Chromosome Aneuploidies (SCA) Screening: The Big Change—OPT-IN Required (12:30–18:20)

• SCA screening (Turner, Klinefelter, Triple X, Jacobs, etc.) is no longer “check the box”:
  • Patients must opt-in after explicit counseling on the test’s limitations and clinical implications.
• Why opt-in? The accuracy (positive predictive value, PPV) for SCA with cfDNA is substantially less than for common autosomal trisomies.
• Clinicians must explain:
  • Higher false positive rate for SCA (due to maternal mosaicism, confined placental mosaicism, etc.).
  • Specific limitations differ from trisomies 21/18/13.

  “By asking them to opt in, it now puts the challenge and the task on us to do our job, which is tell them the limitations of cell free DNA for sex chromosome abnormalities.” (03:45)

5. SCA: Test Accuracy & Counseling Pearls (18:20–27:00)

• PPV for SCA is variable and generally lower than that for autosomal trisomies:
  • Turner syndrome (45,X): PPV ~32%
  • Triple X (47,XXX): PPV ~57%
  • Klinefelter (47,XXY): PPV ~67%
  • Other rare variants can vary
• Maternal mosaicism is a key reason for false positives—approx. 8.6% incidence in one study.
• Test is much more sensitive for Y chromosome abnormalities than X chromosome:

  “Cell free DNA is much more sensitive and specific for disorders involving the Y chromosome than those involving the X chromosome, because it's living in a sea of X chromosomes, which is the mother.” (24:15)

• Other causes for abnormal results include maternal cancer (rare), transfusions, transplants, or even fibroids.
• Clinical pearl: Always interpret SCA results in context; heavily weigh patient age and result-specific PPV.

6. What To Do with an Abnormal SCA Result (27:10–32:00)

• First step: Reassure and counsel patient about high false positive rate.
• Next steps:
  1. Consider diagnostic fetal testing (e.g., amniocentesis) to confirm.
  2. If the result involves X chromosome (Turner or Triple X), consider maternal karyotype to check for mosaicism.
  3. Involve genetics and/or MFM specialists as needed.
• Always review the specific PPV for the exact abnormality detected—each lab report includes this crucial statistic.

7. cfDNA for Fetal Sex Determination—NOT for Nonmedical Use (32:00–34:10)

• Over-the-counter or “direct-to-consumer” (DTC) tests available for fetal sex are NOT recommended for nonmedical, entertainment-only purposes due to:
  • Potential for misleading results and lack of pre-test counseling.
  • Tests target only Y chromosome detection—not a substitute for full SCA screening.

  “The non medical use of cell free DNA solely for fetal sex determination is not recommended.” (34:10; also 06:20, 33:30)

• Analogy: 3D ultrasounds are legitimate clinical tools but should not be used as "keepsake" without proper counseling.

8. Practice Recommendations Recap (35:00–end)

• Eight key recommendations:
  1. Offer cfDNA screening for trisomies 21, 18, 13 to all patients with pre-test counseling.
  2. SCA screening must be opt-in with explicit, documented counseling.
  3. Do NOT use cfDNA for microdeletions or large genome-wide deletions/duplications.
  4. cfDNA for trisomies appropriate in twins (but NOT for SCA or higher-order multiples).
  5. If abnormal SCA result: confirm with diagnostic test and consider maternal testing.
  6. Over-the-counter cfDNA as entertainment or for solely sex determination is not endorsed.
• Sensitivity, specificity, and positive predictive value are not interchangeable—understand and explain limitations to patients.

Notable Quotes & Memorable Moments

• “The non medical use of cell free DNA solely for fetal sex determination is not recommended.” (Host quoting SMFM/ACOG, 06:20, 34:10)
• “By asking them to opt in, it now puts the challenge and the task on us to do our job, which is tell them the limitations of cell free DNA for sex chromosome abnormalities.” (03:45)
• “[For SCA] The accuracy...is not as good as it is for autosomal trisomies. And that's the catch.” (20:45)
• “Cell free DNA is much more sensitive and specific for disorders involving the Y chromosome than those involving the X chromosome.” (24:15)
• “Microdeletion screening using cell free DNA is still not recommended.” (07:50, repeated multiple times as “Say it twice!”)

Humor:

• “It’s science. As Ron Burgundy would say.” (throughout)
• “If you don’t know who Ron Burgundy is…that’s tragic!” (09:59)

Timestamps for Critical Segments

• 00:36: Introduction to new ACOG Practice Advisory
• 03:45: The rationale and mechanics behind opt-in for SCA screening
• 09:59: Recap on what’s unchanged in aneuploidy screening recommendations
• 12:30: Clarification on singletons, twins, and higher-order multiple gestations
• 18:20: Detailed discussion on SCA counseling, test accuracy, and maternal mosaicism
• 27:10: Stepwise management of an abnormal SCA screening result
• 32:00: Direct-to-consumer fetal sex testing and official recommendations
• 34:10: Quote reiteration: cfDNA not for pure fetal sex determination use
• 35:00: Final recap of major practice points

Language & Tone

• Dr. Chapa’s delivery is energetic, colloquial, and practical—laced with humor (“It’s science!”), analogies, and direct advice aimed at clinicians in the trenches, students, and residents.
• Repetition is used intentionally to reinforce key clinical pearls.

Take-Home Clinical Pearls

• cfDNA remains the gold standard for trisomies 21, 18, 13—offer to all, with counseling.
• Screening for sex chromosome aneuploidies now requires specific, documented opt-in consent (not automatic).
• Do NOT use cfDNA for microdeletion screening or for nonmedical fetal sex determination.
• False positives for SCA are far more common than with trisomies, mainly due to maternal factors.
• Abnormal SCA results require confirmatory diagnostic testing and possibly maternal karyotyping.
• cfDNA in twins OK for trisomies, NOT for SCA; NOT for higher-order multiples.
• Always counsel—science is powerful, but it must be used responsibly.

End of Summary.

For further details and specific scenarios, listen to Dr. Chapa’s OBGYN Clinical Pearls, and refer directly to the 2026 ACOG Practice Advisory and SMFM Consult Series 74.