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 ...

Twins are individuals who learn to share before they are born. More often than not, sharing is natural or inevitable for twins because they are conceived and born together and in most situations share ...

While many people think of twins as a rare "double blessing" decided purely by luck, science suggests that your biological clock might actually be stacking the deck. As more women choose to start ...