Chromosomal discordance in monochorionic twins: clinical insights from a case series

Authors

  • Beatriz Sousa Ferreira Obstetrics and Gynecology Department, Unidade Local de Saúde de Trás-os-Montes e Alto Douro https://orcid.org/0000-0002-4468-9642
  • Márcia Marinho Prenatal Diagnosis Center - Obstetrics and Gynecology Department, Unidade Local de Saúde de Gaia e Espinho
  • Carla Duarte Prenatal Diagnosis Center - Obstetrics and Gynecology Department, Unidade Local de Saúde de Gaia e Espinho
  • Cristina Godinho Prenatal Diagnosis Center - Obstetrics and Gynecology Department, Unidade Local de Saúde de Gaia e Espinho
  • Conceição Brito Prenatal Diagnosis Center - Obstetrics and Gynecology Department, Unidade Local de Saúde de Gaia e Espinho https://orcid.org/0009-0007-2042-3659

DOI:

https://doi.org/10.25753/BirthGrowthMJ.v35.i2.44836

Keywords:

karyotype, monochorionic twins, mosaicism, prenatal diagnosis, trisomy 13, turner syndrome, twin pregnancy

Abstract

Monochorionic twin pregnancies are traditionally considered genetically identical due to their monozygotic origin. However, emerging evidence demonstrates that postzygotic chromosomal divergence may lead to significant karyotypic and phenotypic discordance.
We report two cases of monochorionic diamniotic twin pregnancies with discordant chromosomal abnormalities affecting only one fetus. In both cases the co-twin maintained a structurally and genetically normal profile. In the first case, one fetus presented mosaic monosomy X with severe hydrops, while the co-twin was structurally and genetically normal. Selective reduction was performed, followed by intrauterine demise of the co-twin. In the second case, one fetus had trisomy 13 with multiple structural anomalies, while the co-twin had a normal phenotype and favorable outcome after expectant management.
These two cases illustrate that chromosomal discordance may occur in monochorionic twin pregnancies and highlight the diagnostic challenges associated with discordant findings.

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Published

2026-07-24

How to Cite

1.
Sousa Ferreira B, Marinho M, Duarte C, Godinho C, Brito C. Chromosomal discordance in monochorionic twins: clinical insights from a case series. BGMJ [Internet]. 2026 Jul. 24 [cited 2026 Aug. 9];35(2):101-7. Available from: https://revistas.rcaap.pt/bgmj/article/view/44836

Issue

Vol. 35 No. 2 (2026)

Section

Clinical Case Reports

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Copyright (c) 2026 Beatriz Sousa Ferreira, Márcia Marinho, Carla Duarte, Cristina Godinho, Conceição Brito

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