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 ...

It is a simple decision and an obvious one for parents to see their twins as different and in need of certain special types of attention and communication. But there are serious consequences to how ...

Mono-mono twins are an incredibly rare type of identical twins who share both a placenta and an amniotic sac. While this makes for a high-risk pregnancy, advances in monitoring and treatment have ...

Twins may often make you imagine two babies with the exact physical features, such as eyes, smile, and even voice. However, this is not the case with every twin, as some look totally different from ...

Fascination with twins and what twin studies tell us about human nature is universal. There is no question that behavioral and medical science advances have happened largely because twins yield a ...

Carrying a twin pregnancy is not an uncommon event. It occurs when the uterus carries two fetuses simultaneously rather than one. Having twins runs in some families and age also appears to be a ...

The Science of Siblings is a new series exploring the ways our siblings can influence us, from our money and our mental health all the way down to our very molecules. We'll be sharing these stories ...

Twin estrangement starts with unresolved anger between twins in childhood. Perhaps one twin is favored over the other twin for parental personal reasons. Another explanation is that one twin is in ...