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Zygosity misclassification of twins at birth in Japan

Syuichi Ooki1, Yoshie Yokoyama, Akio Asaka

  • 1Department of Health Science, Ishikawa Prefectural Nursing University, Kahoku, Japan. sooki@kj8.so-net.jp

Twin Research : the Official Journal of the International Society for Twin Studies
|June 15, 2004
PubMed

Insights

Many monozygotic twins in Japan are misclassified as dizygotic at birth. This common zygosity misclassification, often based on placental count, affects approximately 25-30% of identical twins.

Area of Science:

  • Reproductive Medicine
  • Genetics
  • Obstetrics

Background:

  • Twinning rates are increasing globally, including in Japan.
  • Zygosity misclassification at birth is a significant, yet understudied, issue.
  • Accurate zygosity determination is crucial for various medical and research purposes.

Purpose of the Study:

  • To investigate the rate of zygosity misclassification in twins born in Japan.
  • To identify factors contributing to misclassification, particularly the role of placental assessment.
  • To highlight the implications of misclassification for understanding twin populations.

Main Methods:

  • Analysis of four independent Japanese twin samples.
  • Comparison of zygosity determined at birth with later assessments (implied).
  • Statistical association analysis between placental number and zygosity.

Main Results:

  • Approximately 25-30% of monozygotic twins were misclassified as dizygotic at birth.
  • This misclassification rate aligns with the incidence of monozygotic twins with dizygous placentation.
  • Obstetricians' assessment of zygosity, based on placental count, showed a strong correlation with actual zygosity.

Conclusions:

  • A substantial proportion of monozygotic twins in Japan are misclassified at birth.
  • Reliance on placental number by obstetricians is a primary driver of this misclassification.
  • Improved diagnostic methods are needed to ensure accurate zygosity determination in newborns.

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