Development of Twins

What is the primary difference in origin between fraternal (dizygotic) and identical (monozygotic) twins?

• Fraternal twins result from one egg fertilized by two sperm, while identical twins result from two eggs fertilized by one sperm.

• Fraternal twins result from two separate eggs fertilized by two separate sperm, while identical twins result from a single zygote splitting into two embryos.

• Fraternal twins result from a single zygote splitting into two embryos, while identical twins result from two separate eggs fertilized by two separate sperm.

• Fraternal twins are always different sexes, while identical twins are always the same sex.

Which of the following factors is associated with an increased likelihood of fraternal twinning?

• Lower levels of Follicle-Stimulating Hormone (FSH).

• Mothers being younger than 30 years old.

• Shorter, more frequent menstrual cycles.

• A family history of identical twins.

What is the approximate global rate of identical twin births per 1000 births?

• 10 per 1000 births.

• 4 per 1000 births.

• 20 per 1000 births.

• 1 per 1000 births.

If identical twins are monochorionic-monoamniotic, what does this imply about their development?

• They developed from two separate zygotes and have separate placentas and amniotic sacs.

• They developed from a single zygote, sharing a single placenta but having separate amniotic sacs.

• They developed from a single zygote, sharing both a single placenta and a single amniotic sac.

• They developed from two separate zygotes, sharing a single placenta but having separate amniotic sacs.