Doctors have documented what they say is only the world's second known case of "semi-identical" twins. The boy and the girl, now four, from Brisbane, in Australia, are identical on their mother's ...

The special relationship between twins allows researchers to examine the differences between genetic and environmental influences over both physical and mental health, as well as traits and behaviors.

Learn why identical twins are almost always the same sex, though they may be different genders. Although there are some rare exceptions, identical twins are almost always the same sex. Because ...

Jedidiah Duggar and Katelyn Nakatsu were the first Duggar couple to welcome twins. They announced their big news and held a gender reveal for both babies. Welcoming two little girls was something ...

There are many parents would love to conceive twins. Isn’t it just adorable to have two little people who look exactly the same? There are two types of twins, identical and fraternal twins.