🌱 A Hopeful Start: PGT-A Tested Embryo, A Healthy Pregnancy
This is a real-life surrogacy case involving a false positive NIPT Trisomy 13 result that shocked a hopeful intended mother-to-be—despite transferring a PGT-A-tested embryo. The embryo her surrogate transferred had passed Preimplantation Genetic Testing for Aneuploidy (PGT-A)—screened and labeled as chromosomally normal. The embryo implanted successfully, and the pregnancy progressed smoothly.
With each heartbeat, she allowed herself to hope a little more.
😟 At 14 Weeks: An Alarming NIPT Result for Trisomy 13
At 14 weeks gestation, the surrogate underwent Non-Invasive Prenatal Testing (NIPT)—a widely used screening that analyzes cell-free DNA from the placenta for chromosomal abnormalities.
To L.’s shock and heartbreak, the NIPT result came back high risk for Trisomy 13.
Trisomy 13 (Patau syndrome) is a serious condition often associated with severe physical and intellectual disability. The news brought waves of panic. How could this happen? The embryo was PGT-A tested. Was there a mistake? Was the baby truly affected?
The days that followed were filled with anxiety, fear, and endless questions. L. consulted with genetic counselors, reviewed every medical detail, and tried to prepare herself for the worst—all while clinging to a thin thread of hope.
🧬 The Truth Revealed: Amniocentesis Results
Understanding that NIPT is a screening tool, not a diagnostic test, L. proceeded with amniocentesis—a diagnostic test performed by extracting amniotic fluid to analyze the fetus’s own chromosomes directly.
Several weeks later, the results came in.
The fetus had a normal chromosomal profile. There was no Trisomy 13.
Tears of relief flowed. The heavy weight lifted, if only slightly at first. A subsequent detailed anatomy scan revealed no structural anomalies. L. could finally breathe again.
🧠 What This Case Teaches Us
This experience illuminated several key realities:
1. PGT-A, NIPT, and Amniocentesis Test Different Things
This case perfectly illustrates why results can differ. The most likely reason is Confined Placental Mosaicism (CPM).
- PGT-A tests a few cells from the trophectoderm (the part of the embryo that becomes the placenta).
- NIPT analyzes cell-free DNA, which comes almost entirely from the placenta as a whole.
- Amniocentesis tests cells shed from the fetus itself.
In L.’s case, the placenta likely contained some Trisomy 13 cells (a mosaic), which triggered the high-risk NIPT result, while the fetus itself was chromosomally normal. This shows that even a “normal” PGT-A result isn’t a 100% guarantee, as it only samples a tiny portion of the future placenta.
2. NIPT Has Limitations, Especially for Trisomy 13
NIPT is an excellent tool for early screening, but its accuracy varies across conditions. The Positive Predictive Value (PPV) is key—it tells you the chance that a high-risk result is a true positive.
ConditionSensitivitySpecificityPositive Predictive Value (PPV)*Trisomy 21~99.3%>99.9%~91%Trisomy 18~97.4%>99.9%~77%Trisomy 13~87.5%>99.9%~40%
*Note: PPV depends heavily on maternal age and the prevalence of the condition.
A 40% PPV for Trisomy 13 means that more than half of positive NIPT results for this condition may actually be false positives.
3. Don’t Panic—Seek Diagnostic Confirmation
If your NIPT flags a high-risk result, remember: it’s not a diagnosis. Speak with a genetic counselor. Confirm with a diagnostic test like amniocentesis or CVS before making any major decisions.
✅ FAQ: False Positive Trisomy 13 on NIPT During Surrogacy
1. Can NIPT be wrong about Trisomy 13?
Yes. Although NIPT is highly accurate for Trisomy 21, its positive predictive value (PPV) for Trisomy 13 is only about 40%, meaning more than half of positive results could be false.
2. Why did NIPT show Trisomy 13 if the baby is healthy?
False positives can happen due to placental mosaicism, vanishing twins, or technical limitations. NIPT analyzes placental DNA, which may not perfectly represent the fetus.
3. What should I do if I get a high-risk NIPT result?
Don’t panic. Talk to a genetic counselor and consider diagnostic testing like amniocentesis, which directly examines fetal chromosomes and can confirm or rule out the condition.
4. Is NIPT a diagnostic test?
No, NIPT is a screening test. It estimates risk but does not provide a definitive diagnosis. Only amniocentesis or chorionic villus sampling (CVS) can confirm chromosomal conditions.
5. Is PGT-A always reliable?
PGT-A is helpful but not foolproof. It may miss low-level mosaicism, and some embryos labeled as “normal” can still lead to false NIPT results or other surprises later in pregnancy.
6. How accurate is NIPT for different conditions?
NIPT is most accurate for Trisomy 21 (~91% PPV), less so for Trisomy 18 (~77%), and even less for Trisomy 13 (~40%), depending on maternal age and population risk.
💬 Final Thoughts
L.’s journey is one of resilience, uncertainty, and ultimately—relief. Her story reminds us that while medical technology is incredibly advanced, no test is absolute. We must approach each result with context, caution, and the right follow-up.
📚 References
- ACOG Practice Bulletin No. 226: Screening for Fetal Chromosomal Abnormalities. (2020). Obstetrics & Gynecology, 136(4), e49-e67.
- Benn, P., Borrell, A., Chiu, R. W. K., et al. (2022). Position statement from the International Society for Prenatal Diagnosis on the use of genome-wide NIPT. Prenatal Diagnosis, 42(2), 182–188.
- Bianchi, D. W., et al. (2014). DNA sequencing versus standard prenatal aneuploidy screening. New England Journal of Medicine, 370(9), 799–808.
- Gil, M. M., Quezada, M. S., Revello, R., et al. (2015). Analysis of cell-free DNA in maternal blood in screening for fetal aneuploidies: updated meta-analysis. Ultrasound in Obstetrics & Gynecology, 45(3), 249–266.
