________ twins- zygote splits 5-10 days after fertilization

________ twins- zygote splits 5-10 days after fertilization

• A. Dichorionic/ Diamniotic
• B. Monochorionic/ Diamniotic
• C. Monochorionic/ Monoamniotic
• D. Dizygotic

Answer: (B)

Timing of zygote splitting determines how the placenta and sacs are arranged in monozygotic twins. When the zygote splits after the chorion has formed but before the amnion fully separates, you end up with monochorionic/diamniotic twins: one shared placenta (chorion) but two amniotic sacs (two amnions). Splitting around 5–10 days after fertilization fits this pattern, so the description that best matches is monochorionic/diamniotic. On ultrasound you’d see a single placental mass with two separate amniotic sacs separated by a thin dividing membrane. This contrasts with very early splitting, which yields dichorionic/diamniotic (two placentas, two sacs), later splitting leading to monochorionic/monoamniotic (one sac), or splitting so late that conjoined twins form.

Timing of zygote splitting determines how the placenta and sacs are arranged in monozygotic twins. When the zygote splits after the chorion has formed but before the amnion fully separates, you end up with monochorionic/diamniotic twins: one shared placenta (chorion) but two amniotic sacs (two amnions). Splitting around 5–10 days after fertilization fits this pattern, so the description that best matches is monochorionic/diamniotic. On ultrasound you’d see a single placental mass with two separate amniotic sacs separated by a thin dividing membrane. This contrasts with very early splitting, which yields dichorionic/diamniotic (two placentas, two sacs), later splitting leading to monochorionic/monoamniotic (one sac), or splitting so late that conjoined twins form.