Step 1

Enbryology 2

A 29-year-old pregnant woman presents to the obstetrician for prenatal care. She is currently at 26 weeks’ gestation, and this is her first prenatal visit. Her pregnancy has been uneventful so far. Past medical history is unremarkable, and she does not take any medications. The in-office ultrasound indicates the presence of two anatomically separate fetuses with individual amnions. Further study indicates the twins are sharing a placental blood supply.

Which of the following most accurately describes these twins?

  • A) Dizygotic
  • B) Monozygotic, split before day 4
  • C) Monozygotic, split between days 4 and 8
  • D) Monozygotic, split between days 8 and 12
  • E) Monozygotic, split after day 12


Alexandra Conway


Dr. Ted O'Connell

Last updated

Apr 15, 2023


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