Meet the Clydesdale. The Clydesdale breed once almost faced extinction. Even though there is little practical use for heavy horses today because their muscle power has been replaced by machinery, breeders and enthusiasts have ensured that the breed is increasing, rather diminishing in numbers.
1 Over the three decades, the twin birth rate rose by 76 percent, from 18.9 to 33.2 per 1,000 births (or from 1.9 percent to 3.3 percent of all births) (Figure 1). 2  Increases in the twin birth rate averaged more than 2 percent a year from 1980 through 2004 (peaking at more than 4 percent from 1995 to 1998).
A 23 year study conducted at four US medical centers used information from 1,612 twin pregnancies where twins were born after 28 weeks to come up with the following statistics: 1  Chances of extremely preterm (28-30 weeks): 5.3%. 2  Chances of very preterm (31-32 weeks): 8.5%.