Use these charts for a rough estimate on the chances of having twins or triplets. While we can't vouch for the complete accuracy of these percentages, they are based on the latest numbers available on twin births from the National Vital Statistics Reports (1997) and (1999). Some of the numbers below are also courtesy of the Facts About Multiples Web Site.

Note that the numbers for specific age groups are for all reported twin births in the United States - they take into account both twins conceived naturally and those via fertility drugs or IVF treatment. As a result, the odds of conceiving twins naturally - and carrying to full term - are most likely lower than represented below.

And remember, just because mom or pop is a twin doesn't mean two are on the way. There is no way whatsoever to predict identical twins so a mom who is an identical twin has no better chance of producing twins than any other women. And the twinning gene is carried on the female side, so dad doesn't have much to do with it.

The general rules of thumb are the older the mom, the better chance of having twins. And if fraternal twins are on the women's side of the family, your odds increase dramatically as well (and as you can see below, don't think that delivering one set of fraternals means you're immune from delivering a second set).