In the answers to the questions below, the following words are synonyms and may be used interchangeably:

• Identical twin = monozygotic = MZ
• Fraternal twin = dizygotic = DZ

For more information about these terms, see the Zygosity section.

Occurrence of Twins

• How often do twin births occur?
• Why is the number of twins increasing?
• Are there more male twins or female twins?
• I am a twin. Do I have an increased chance of having twins?
• Twins run in my family. Do I have an increased chance of having twins?
• What factors are related to fraternal (DZ) twinning?
• Does identical (MZ) twinning run in families?

Appearance of Twins

• Can identical twins look different?
• Do female identical twins appear more different than male identical twins?
• Can fraternal twins look so similar that they are mistaken for identical?
• Can a male/female twin pair be identical twins?
• Can twins be of different races?

Types of twins

• What are mirror image twins?
• What is a hidden twin?
• What are half-identical twins?

Medical Questions for Twins

• What is twin-to-twin transfusion syndrome?
• If my twin gets a disease, will I also get it?
• What causes some twin pairs to be born with very different birth weights?

Fun Facts about Twins

• Do identical twins have identical fingerprints?
• Do identical twins always have the same hand preference?
• Can twins have different birthdays?
• Can twins read each other’s minds?
• Can twins have different fathers?