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 Even though there is little practical use for heavy horses today because their muscle power has been replaced by machinery, breeders and enthusiasts have ensured that the breed is increasing, rather diminishing in numbers.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).
Among non-twin births, male singletons are slightly (about five percent) more common than female singletons. The rates for singletons vary slightly by country. For example, the sex ratio of birth in the US is 1.05 males/female, while it is 1.07 males/female in Italy.However, males are also more susceptible than females to die in utero, and since the death rate in utero is higher for twins, it leads to female twins being more common than male twins.n the uterus, a majority of monozygotic twins (60â70%) share the same placenta but have separate amniotic sacs. In 18â30% of monozygotic twins each fetus has a separate placenta and a separate amniotic sac. A small number (1â2%) of monozygotic twins share the same placenta and amniotic sac.