ask the experts: twin myths

Lynn Shizumura
June 06, 2019

Jeanine Morioka’s family is full of twins. She has a fraternal twin sister. Her husband has twin siblings. And the Moriokas have identical twin boys, Brayden and Bronson, who start high school in the fall.

Growing up, Morioka was often compared to her sister. Her boys have a similar experience, especially since they play the same sports and are in the same classes. Morioka, who conceived twins naturally, says she was often asked why she was having twins when she was a twin. People assumed twins skipped a generation. 

The Morioka family.

If you’re a twin or know twins, you’ve probably heard similar questions. To set the record straight on a few of them, we asked two local obstetricians and gynecologists—Christina Arnett, M.D., and Simon Chang, M.D.—for answers. 

Does having twins skip a generation or run in families?

CA: Conceiving twins doesn’t follow a predictable generational pattern. However, if your sister has fraternal twins, you’re about 2.5 times more likely than the average woman to have them, too. If your brother has twins, your likelihood is about the same as everyone else. 

In addition to family history, women in their 30s and 40s are more likely to have fraternal twins than younger women because they’re more likely to ovulate more than one egg in a given month. Similarly, women undergoing fertility treatments may ovulate two or three eggs in a treatment cycle, which helps them get pregnant but also increases their chances of conceiving twins.

Do twins have extrasensory perception (ESP)?

SC: No. Twins often share a bond that’s closer than most siblings. There are anecdotal stories of ESP or a special connection, but there’s no evidence to support them.

Are identical twins always the same gender?

SC and CA: Yes. Identical twins come from one fertilized egg that splits into two. They’re always the same gender except for extremely rare cases. Fraternal twins come from two separate eggs that are fertilized. They can either be the same or different genders.

Do identical twins always look the same, like Mary-Kate and Ashley Olsen?

SC and CA: Identical twins generally look like each other but there may be differences in their appearance due to environmental factors.

Interestingly, Mary-Kate and Ashley Olsen are not identical twins! The Olsen twins are fraternal twins who look very similar. Essentially, they are as genetically similar as any two siblings, they just happen to be siblings of the same age, which may contribute to the impression that they’re identical.

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