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PubMed This is a summary of 13 peer-reviewed journal articles Updated
Obstetrics · Triploidy

Two Types of Triploidy: Diandric and Digynic

At a Glance

Triploidy is classified into two types: diandric (extra paternal chromosomes) and digynic (extra maternal chromosomes). Diandric triploidy often causes a large, cystic placenta and maternal health risks like preeclampsia. Digynic triploidy typically results in a small placenta and severe fetal growth restriction.

While all triploidy involves having 69 chromosomes, there are two distinct types based on where that extra set of 23 chromosomes came from. These two types—diandric and digynic—develop differently and carry different risks for your own health. Understanding which type is present helps your medical team provide you with the most appropriate care.

Diandric Triploidy (Paternal Origin)

In diandric triploidy, the extra set of chromosomes comes from the father [1]. This usually happens because two sperm fertilized a single egg (a process called dispermy) [1][2].

What to Expect on Ultrasound

  • The Placenta: The hallmark of the diandric type is a very large, thickened, and abnormal placenta [1][3]. On an ultrasound, it may look “cystic” or like a bunch of grapes [1].
  • Partial Hydatidiform Mole: This abnormal placental growth is known as a partial hydatidiform mole [1]. The abnormal tissue can produce extremely high levels of pregnancy hormones (hCG) [1].
  • Fetal Growth: While the placenta is often large, the baby typically develops closer to the expected size for their age initially [4].

Digynic Triploidy (Maternal Origin)

In digynic triploidy, the extra set of chromosomes comes from the mother [5]. This most commonly occurs when the egg fails to discard extra chromosomes during its development [5][2].

What to Expect on Ultrasound

  • The Placenta: Unlike the diandric type, the placenta in a digynic pregnancy is usually very small and does not show molar (cystic) changes [6][7].
  • Severe Growth Restriction: The baby often experiences severe growth restriction (IUGR), meaning they are much smaller than expected for their stage of development [6][8].
  • Relative Macrocephaly: A common finding is that the baby’s head appears large in comparison to the rest of their body [6][9].
  • Physical Markers: Doctors may look for webbing of the third and fourth fingers or toes (syndactyly), which is a classic marker for this condition [4][9].

Why the Type Matters for Your Health

Distinguishing between these two types is vital because the diandric type carries specific medical risks for the mother [1].

  1. Hormonal Complications: The abnormal placental growth in diandric triploidy leads to high hCG levels, which may cause severe morning sickness (hyperemesis gravidarum) or an overactive thyroid (hyperthyroidism) [1][10].
  2. Preeclampsia: Women with the diandric type have a much higher risk of developing early-onset preeclampsia, a dangerous condition characterized by high blood pressure and potential damage to organ systems [1][11].
  3. Follow-up Care: If a partial mole is confirmed, you will need regular blood tests after the pregnancy to ensure your hCG levels drop to zero [1]. This ensures no abnormal placental tissue remains [10].

In contrast, the digynic type generally does not carry these specific molar risks [6]. Your doctor may use specialized genetic testing to confirm which type is present [12][13].

Common questions in this guide

What is the difference between diandric and digynic triploidy?
Diandric triploidy occurs when the extra set of chromosomes comes from the father, often causing a large, abnormal placenta. Digynic triploidy happens when the extra chromosomes come from the mother, typically resulting in a small placenta and severe fetal growth restriction.
What does diandric triploidy look like on an ultrasound?
On an ultrasound, diandric triploidy usually shows a very large, thickened placenta that may look like a bunch of grapes. The baby generally develops closer to the expected size for their age during the early stages of pregnancy.
What are the signs of digynic triploidy on an ultrasound?
Digynic triploidy typically presents with a very small placenta and a baby that is measuring much smaller than expected. The baby's head may also appear disproportionately large compared to their body, and doctors may notice webbing of the fingers or toes.
Are there risks to the mother's health with triploidy?
Yes, diandric triploidy carries specific maternal health risks due to abnormal placental growth producing high hormone levels. These risks include severe morning sickness, an overactive thyroid, and early-onset preeclampsia, which requires careful medical monitoring.
Why do I need blood tests after a partial molar pregnancy?
If diandric triploidy causes a partial hydatidiform mole, you will need regular blood tests after the pregnancy to track your hCG hormone levels. This ensures your levels drop to zero and that no abnormal placental tissue remains in your body.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Based on the ultrasound, does the placenta look enlarged or cystic, or is it small and underdeveloped?
  2. 2.Does the baby's growth pattern show a large head relative to the body, which is common in the digynic type?
  3. 3.Is this pregnancy classified as a partial hydatidiform mole, and how does that change my follow-up care?
  4. 4.What symptoms of preeclampsia or hyperthyroidism should I be watching for at home?

Questions For You

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References

References (13)
  1. 1

    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
  2. 2

    Validation of a targeted next generation sequencing-based comprehensive chromosome screening platform for detection of triploidy in human blastocysts.

    Marin D, Zimmerman R, Tao X, et al.

    Reproductive biomedicine online 2018; (36(4)):388-395 doi:10.1016/j.rbmo.2017.12.015.

    PMID: 29366772
  3. 3

    Molecular genetic study of triploidy and the hydatidiform mole in pregnancy loss: analysis of 10,000 consecutive cases.

    Pushkarev VP, Masycheva AS, Glazyrina EA, et al.

    Vavilovskii zhurnal genetiki i selektsii 2025; (29(5)):621-628 doi:10.18699/vjgb-25-67.

    PMID: 41000402
  4. 4

    Triploidy: Variation of Phenotype.

    Toufaily MH, Roberts DJ, Westgate MN, Holmes LB

    American journal of clinical pathology 2016; (145(1)):86-95 doi:10.1093/ajcp/aqv012.

    PMID: 26712875
  5. 5

    Prenatal Diagnosis of Triploidy in Fetus with Unexpected Chromosomal Translocation of Maternal Origin.

    Jadhav A, Jadhav Y, Bhairi V, et al.

    International journal of molecular and cellular medicine 2023; (12(1)):81-85 doi:10.22088/IJMCM.BUMS.12.1.81.

    PMID: 37942256
  6. 6

    Digynic triploidy in a fetus presenting with semilobar holoprosencephaly.

    Chuang TY, Chang SY, Chen CP, et al.

    Taiwanese journal of obstetrics & gynecology 2018; (57(6)):881-884 doi:10.1016/j.tjog.2018.11.001.

    PMID: 30545546
  7. 7

    Triploidy in a Live-Born Extremely Low Birth Weight Twin: Clinical Aspects.

    Vakrilova L, Hitrova-Nikolova S, Bradinova I

    Journal of pediatric genetics 2022; (11(3)):227-231 doi:10.1055/s-0040-1716828.

    PMID: 35990033
  8. 8

    Digynic triploidy: utility and challenges of noninvasive prenatal testing.

    Fleischer J, Shenoy A, Goetzinger K, et al.

    Clinical case reports 2015; (3(6)):406-10 doi:10.1002/ccr3.247.

    PMID: 26185638
  9. 9

    Prenatal diagnosis of syndromic alobar holoprosencephaly associated with digynic triploidy fetus.

    Albu CC, Albu DF, Pătraşcu A, et al.

    Romanian journal of morphology and embryology = Revue roumaine de morphologie et embryologie 2020; (61(4)):1309-1316 doi:10.47162/RJME.61.4.32.

    PMID: 34171079
  10. 10

    Maternal complications in molecularly confirmed diandric and digynic triploid pregnancies: single institution experience and literature review.

    Massalska D, Bijok J, Kucińska-Chahwan A, et al.

    Archives of gynecology and obstetrics 2020; (301(5)):1139-1145 doi:10.1007/s00404-020-05515-4.

    PMID: 32219520
  11. 11

    Uncommon Presentation of Triploidy: A Case Report.

    Uzun I, Pata Ö, Unlu C, et al.

    Journal of clinical and diagnostic research : JCDR 2015; (9(10)):QD01-2 doi:10.7860/JCDR/2015/14037.6553.

    PMID: 26557571
  12. 12

    Usefulness of methylation-specific multiplex ligation-dependent probe amplification for identification of parental origin of triploidy.

    Massalska D, Ozdarska K, Bijok J, et al.

    Journal of human genetics 2020; (65(10)):889-894 doi:10.1038/s10038-020-0784-0.

    PMID: 32483273
  13. 13

    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

This page provides educational information about the types of triploidy and their ultrasound findings. Always consult your maternal-fetal medicine specialist or obstetrician for advice on your specific diagnosis and maternal health risks.

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