Find out everything you've always wanted to know about identical twins – from how they form to what makes them unique.

Even fewer cases of semi-identical (sesquizygotic) twins have been reported in medical literature. In these cases, a single egg is fertilized by two sperm. The egg then divides and develops into ...

It is the first time semi-identical twins have been identified during pregnancy. The first-time mother was 28 at the time and had conceived naturally, doctors said. The case is being reported on ...