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Twin Babies Identical Not Due to Fertility Drugs

Dear Dr. Dave and Dr. Dee,

A coworker has identical twins. Would it be rude if I asked her if she took fertility drugs, which caused the twins, or is that too personal?


Just Curious

Dear Just Curious,

Asking someone if they took fertility drugs is a very personal question. Unless someone brings up the subject of infertility, it is normally a private matter between the couple.

However, you don't need to wonder about your coworker's twins. Your coworker's identical twins were not a result of fertility drugs. Infertility treatment medications can increase the odds of having twins, but only non-identical twins, not identical twins. Identical twins develop from one egg (monozygotic) whereas non-identical (fraternal) twins develop from two separate eggs (dizygotic).

The possibility of conceiving twins increases when fertility drugs are used because the drug stimulates the ovaries to produce more than one egg, and therefore the possibility of non-identical twins. However, multiple eggs can also be released without the use of fertility drugs.

Multiple Births Canada ( estimates that overall, 15-17% of multiple births result from infertility treatment. But, it is the higher order multiples of three or more babies that are the result of infertility treatment. "It is estimated that 60% of triplets, 90% of quadruplets and 99% of quintuplets result from infertility treatments" (Multiple Births Canada, 2004).

For more information about multiple births, go to