Experts told the Boston Globe that the ranking is a combination of demography and technology. Women who give birth in Massachusetts are more likely to be older -- and more likely to have multiple births -- and to be using techniques to assist conception which also increases multiples.

About 4.5 percent of the live births in Massachusetts are twins, while the national average is 3.2 percent. New Jersey and Connecticut, also high-income northeastern states, are tied for second place at 4.2 percent.

The National Organization of Mothers of Twins Clubs plans to hold its national convention in Massachusetts in July.

"Massachusetts is the best place to have twins," said Nicole Boloz, a teacher who is raising 5-year-old twins in Southborough, a suburb west of Boston. "To be in an area where there are so many other twin moms really makes a big difference."