Although there are some rare exceptions, identical twins are almost always the same sex. Because identical twins occur when a single fertilized egg splits and forms two embryos, each embryo has the ...

Twins occur in about one out of 90 human pregnancies in the US. As a rule, at conception, one sperm fertilizes a single egg to produce a zygote. Two thirds of twins are fraternal, with fertilization ...

Two embryos split to create two sets of identical twin quadruplets. April 12, 2011— -- "Babies, babies, babies." That's how Miranda and Josh Crawford now describe a typical day after their two ...

CALGARY, Alberta (Reuters) - A 60-year-old woman in the Western Canadian city of Calgary has given birth to twins after going to India for fertility treatments, the Canadian Broadcasting Corp reported ...