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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Obstetrics

How Triploidy is Diagnosed

At a Glance

Standard NIPT often misses triploidy because the extra chromosomes maintain a balanced ratio. Definitively diagnosing triploidy requires direct testing through CVS or amniocentesis. If a pregnancy ends, placental pathology is essential to rule out a molar pregnancy and determine follow-up care.

Understanding how triploidy is diagnosed can be confusing, particularly if early screening tests indicated that everything was normal.

The Role and Limits of Screening (NIPT)

Many parents first encounter potential concerns through Non-Invasive Prenatal Testing (NIPT), a blood test that analyzes fragments of placental DNA floating in the mother’s blood [1].

However, standard NIPT often completely misses triploidy. Standard NIPT works by counting the ratio of chromosomes. Because a triploid baby has a complete extra set of all chromosomes, the ratio remains balanced (1:1:1 instead of 1:1) [2]. To standard NIPT, this looks perfectly normal. Only a specialized version of NIPT (called SNP-based NIPT) can actually detect the presence of the extra chromosomal set [3][2].

Additionally, in cases of digynic triploidy (the maternal type), the placenta is small and doesn’t release much DNA [4]. This can result in a “low fetal fraction,” leading the NIPT to return a “no call” or “unreportable” result [5][6]. While frustrating, a “no call” is often the first signal to doctors to look closer [7][8].

Definitive Diagnostic Tests

To confirm a diagnosis, doctors rely on invasive tests that directly sample the baby’s or placenta’s cells.

  1. Chorionic Villus Sampling (CVS): Usually performed between 10 and 13 weeks, taking a small sample of tissue from the placenta.
  2. Amniocentesis: Typically performed after 15 weeks, collecting a small amount of amniotic fluid.

The lab uses specialized methods on these samples:

  • QF-PCR: A rapid test that counts specific chromosomes to quickly identify triploidy [9][10].
  • Chromosomal Microarray (CMA): A highly detailed test that can definitively see the three sets of chromosomes and even identify which parent they came from [11][12].

Understanding the Pathology Report

If the pregnancy is terminated or ends in miscarriage, a pathology report on the placental tissue provides vital answers about your health risks.

Why They Test the Tissue

The main goal of the pathology report is to determine if the tissue is molar (which requires close follow-up) or non-molar [13].

  • Protein Staining (p57): Pathologists use a special stain to look for a protein called p57 [14]. If p57 is present, it means maternal DNA is present [15][16]. This is important because it rules out a completely different, dangerous condition called a complete molar pregnancy (which has only paternal DNA and no maternal DNA) [14].
  • DNA Fingerprinting (Genotyping): To definitively tell if the triploidy was paternal (diandric) or maternal (digynic), doctors use DNA fingerprinting [16][17]. Knowing this determines whether you need extended monitoring for complications like high blood pressure or persistent placental tissue [13].

While the laboratory mechanics are complex, their purpose is simple: to ensure you receive the correct care for your physical recovery.

Common questions in this guide

Why did my NIPT result say everything was normal if the baby has triploidy?
Standard NIPT works by checking the ratio of chromosomes in the blood. Because a triploid baby has a complete extra set of all chromosomes, the ratio remains balanced and looks perfectly normal to standard screening tests. Only specialized SNP-based NIPT can detect the extra set.
What does a 'no call' NIPT result mean for triploidy?
In maternal (digynic) triploidy, the placenta is usually very small and does not release enough DNA into the mother's blood. This low DNA level leads to a 'no call' or 'unreportable' NIPT result, which often signals doctors to look closer with an ultrasound or diagnostic test.
How is triploidy definitively diagnosed during pregnancy?
Doctors confirm triploidy using invasive diagnostic tests like Chorionic Villus Sampling (CVS) or amniocentesis. These procedures collect direct cellular samples of the placenta or amniotic fluid, allowing labs to definitively map the baby's chromosomes.
Why is a pathology report needed after a triploidy miscarriage or termination?
The pathology report determines if the placental tissue is molar or non-molar. By identifying whether the extra chromosomes came from the mother or the father, doctors can determine if you need extended medical monitoring to prevent complications like high blood pressure.
What does the p57 test check for on my pathology report?
Pathologists use a p57 stain to verify the presence of maternal DNA in the tissue. This is a critical step because it rules out a complete molar pregnancy, a serious condition that contains only paternal DNA and requires specialized follow-up care.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Did my NIPT test use the standard counting method, or was it a SNP-based test?
  2. 2.Which invasive test—CVS or amniocentesis—is more appropriate for my current situation?
  3. 3.Will the pathology report specifically check the tissue to rule out a complete molar pregnancy?
  4. 4.Will genetic testing definitively determine if the triploidy was diandric or digynic?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
  1. 1

    False Negative NIPT Results: Risk Figures for Chromosomes 13, 18 and 21 Based on Chorionic Villi Results in 5967 Cases and Literature Review.

    Van Opstal D, Srebniak MI, Polak J, et al.

    PloS one 2016; (11(1)):e0146794 doi:10.1371/journal.pone.0146794.

    PMID: 26771677
  2. 2

    The value of quantitative fluorescence polymerase chain reaction for the products of conception in the era of copy number variation sequencing.

    Yang S, Zhang H, Wang Y, et al.

    Frontiers in genetics 2025; (16()):1750362 doi:10.3389/fgene.2025.1750362.

    PMID: 41584928
  3. 3

    Non-invasive prenatal screening for fetal triploidy using single nucleotide polymorphism-based testing: Differential diagnosis and clinical management in cases showing an extra haplotype.

    Kantor V, Jelsema R, Xu W, et al.

    Prenatal diagnosis 2022; (42(8)):994-999 doi:10.1002/pd.6169.

    PMID: 35574995
  4. 4

    Unexpected finding of uniparental disomy mosaicism in term placentas: Is it a common feature in trisomic placentas?

    Van Opstal D, Diderich KEM, Joosten M, et al.

    Prenatal diagnosis 2018; (38(12)):911-919 doi:10.1002/pd.5354.

    PMID: 30187503
  5. 5

    Evaluation of repeat testing of a non-sequencing based NIPT test on a Finnish general-risk population.

    Karlsson F, Ahola T, Dahlberg J, et al.

    Acta obstetricia et gynecologica Scandinavica 2021; (100(8)):1497-1500 doi:10.1111/aogs.14125.

    PMID: 33576010
  6. 6

    Factors, pregnancy outcomes, and management associated with non-reportable results in prenatal cell-free DNA testing.

    Yin H, Wang J, Wu X, et al.

    Archives of gynecology and obstetrics 2025; (312(1)):197-205 doi:10.1007/s00404-025-07977-w.

    PMID: 39966114
  7. 7

    Factors associated with test failure in pregnant women undergoing cell-free DNA-based testing for fetal trisomy.

    Chang J, Qi Q, Zhou X, et al.

    Journal of medical screening 2021; (28(4)):411-418 doi:10.1177/09691413211009940.

    PMID: 33884933
  8. 8

    Reply: The missing role of diagnosis of confined placental mosaicism in the management of fetal growth restriction.

    Eggenhuizen GM, Go A, Galjaard RJ

    Human reproduction update 2021; (28(1)):151-152 doi:10.1093/humupd/dmab033.

    PMID: 34642759
  9. 9

    Prenatal Diagnostic Value of Chromosomal Microarray in Fetuses with Nuchal Translucency Greater than 2.5 mm.

    Zhang Z, Hu T, Wang J, et al.

    BioMed research international 2019; (2019()):6504159 doi:10.1155/2019/6504159.

    PMID: 32908864
  10. 10

    [Application of quantitative fluorescencet-PCR in the prenatal diagnosis of chromosomale aneuploidies].

    Qin S, Wang X, Chen X, et al.

    Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 2018; (35(2)):228-231 doi:10.3760/cma.j.issn.1003-9406.2018.02.018.

    PMID: 29652998
  11. 11

    Screening of triploid in miscarriage tissues using medium-coverage whole genome sequencing with a three-algorithm integrated approach.

    Zheng J, Zhang Q, Xu L, et al.

    Journal of assisted reproduction and genetics 2025; (42(9)):3133-3142 doi:10.1007/s10815-025-03607-1.

    PMID: 40750717
  12. 12

    Prenatal diagnosis of maternal uniparental disomy 5 by amniocentesis associated with confined placental mosaicism for trisomy 5 and fetal trisomy 21 in a pregnancy.

    Chen CP, Chern SR, Wang LK, et al.

    Taiwanese journal of obstetrics & gynecology 2020; (59(6)):938-940 doi:10.1016/j.tjog.2020.09.023.

    PMID: 33218416
  13. 13

    The Contribution of QF-PCR and Pathology Studies in the Diagnosis of Diandric Triploidy/Partial Mole.

    Benítez L, Pauta M, Badenas C, et al.

    Diagnostics (Basel, Switzerland) 2021; (11(10)) doi:10.3390/diagnostics11101811.

    PMID: 34679509
  14. 14

    Loss of p57KIP2 expression confers resistance to contact inhibition in human androgenetic trophoblast stem cells.

    Takahashi S, Okae H, Kobayashi N, et al.

    Proceedings of the National Academy of Sciences of the United States of America 2019; (116(52)):26606-26613 doi:10.1073/pnas.1916019116.

    PMID: 31792181
  15. 15

    Clinical Usefulness of Immunohistochemical Staining of p57 kip2 for the Differential Diagnosis of Complete Mole.

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    PMID: 26161420
  16. 16

    Discrepancies Between Pathological Distinction and DNA Genotyping in the Diagnosis of Hydatidiform Moles.

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    Cureus 2025; (17(6)):e85953 doi:10.7759/cureus.85953.

    PMID: 40520843
  17. 17

    Evaluation of Combined p57KIP2 Immunohistochemistry and Fluorescent in situ Hybridization Analysis for Hydatidiform Moles Compared with Genotyping Diagnosis.

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    PMID: 38291567

This page explains triploidy diagnostic testing and pathology reports for educational purposes. Always consult your maternal-fetal medicine specialist or genetic counselor for guidance on your specific prenatal testing results.

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