Prenatal Sonographic Features and Parental Origin of Triploidy

BACKGROUND AND PURPOSE:

  • Triploidy results from an extra haploid chromosome set of paternal (diandric) or maternal (digynic) origin
  • Occurs in 1–2% of all conceptions, with majority resulting in early embryonic/fetal loss
  • McFadden and Kalousek prenatal sonographic assessment
    • Diandric phenotype: Relatively normal-sized fetus with microcephaly or normal head circumference, but abnormally large, cystic placenta
    • Digynic phenotype: Asymmetric fetal growth and non-cystic placenta
  • Massalska et al. (Prenatal Diagnosis, 2017) sought to determine
    • The pattern of sonographic abnormalities in triploid pregnancies
    • The efficacy of McFadden and Kalousek prenatal sonographic assessment

METHODS:

Retrospective case analysis in a single unit between 1997 and 2015

RESULTS:

  • Data analysis of 67 triploidy cases (64 singletons and 3 twins) between 11 and 30 weeks gestation
  • All invasive testing was the result of fetal growth restriction and/or fetal anomalies
    • NT was increased in 25% of fetuses with diandric or undefined phenotype and no fetus with digynic phenotype, consistent with previous research
  • Abnormal ultrasound findings included
    • Fetal growth restriction: 81.5%
    • Oligohydramnios: 50.7%
    • Structural defects: 61.2%
    • Multiple structural anomalies: 35.8%
      • Central nervous system, heart and urinary tract were most common
  • ‘Diandric Phenotype’ was seen in 11.9% of fetuses that presented with cystic placentas
  • ‘Digynic phenotype’ was identified in 70.2% asymmetrically growth-restricted fetuses with non-cystic placentas
  • 17.9% of cases featured both diandric and digynic phenotype
  • There were no live births in this cohort in cases with follow-up due to termination, IUFD or spontaneous miscarriage

CONCLUSION:

  • Almost 40% of triploid fetuses do not appear to have structural abnormalities
  • Diandric triploidy based on previous literature (small ‘n’) carries high risk for maternal complications
    • Preeclampsia and HELLP reported to be between 4 and 35%
    • Molar placenta changes not required
  • In approximately 20% of triploid pregnancies, parental origin cannot be detected using McFadden and Kalousek assessment

Learn More – Primary Sources:

Triploidy – variability of sonographic phenotypes