Daily Mail out by a factor of about four hundred, as per usual

From The Daily Mail:

Now that's double trouble! Woman, 25, beats odds of 170,000 to one by giving birth to twins for the second time

According to Wiki, about one birth in thirty* results in twins. We also know that some people are more likely to have twins than others, it's genetic as well as being related to age of mother, fertility treatment and diet. So if a mother has already had twins, let's assume that the chances of her having twins again is twice as high, maybe one-in-fifteen?

So the chances of any woman having two sets of twins is very approximately 1/30 x 1/15 = 1-in-450. Not 1-in-170,000, FFS.

But congrats to Mrs Power anyway, and I wish them all the best.

* Seems about right. There was a pair of fraternal twins in my class at primary school, and there was also a pair of fraternal twins in my class at secondary school. Was there a pair twins in your class at school?