How Were The Derrico Quintuplets Formed?

When quintuplets are not all the same gender, they could be fraternal quintuplets or a mixture of identical and fraternal. 
Fraternal quintuplets are conceived when five separate eggs are released by the mother and each egg is fertilized by a different sperm. But having quintuplets this way naturally is extremely rare.



Instead, quintuplets of different genders could be a mixture of fraternals and identicals.

In identical twins or triplets, the mother releases an egg which is fertilized by one sperm before splitting to form identical twins or identical triplets.

This means that the Derrico quintuplets could have been formed in a number of ways. All could be from five separate eggs (fraternal) or from as few as two eggs (a set of twins and a set of triplets), three eggs (two sets of twins and another egg), three eggs with a different combination (one set of twins and two other eggs), four eggs (one set of twins and three other eggs) or any similar combination.