How is it possible to have triplets if there are no multiple births in my family?

I'm currently 2 months pregnant and it's triplets. No one in my family has multiple birth and neither nor my husband nor I were on any fertility treatment, none.

We weren't even trying to be honest. I was assuming my childbearing years was nearly dead by now. I gave birth to our daughter at age 35 and it was a difficult pregnancy. Or is it my age producing triplets?

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The doctor already has me as a high risk pregnancy and have several follow-up appointments.
How is it possible to have triplets if there are no multiple births in my family?
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