The quintuplets are a set of five babies born in the same birth. An infant included in such a set is called a five, and sometimes a “five”. While quintuples and other higher-order multiple births (also known as supertwins) are rare, increased use of fertility drugs and assisted reproduction techniques has also led to an increase in these types of pregnancies. Here’s everything you need to know about quintuplets.

Types of Fives. Quintuplets can be fraternal (polygygous), identical (monozygous), or a combination of both. Polyzygous quintuplets result from five unique combinations of eggs and sperm, while monozygotic multiples result from the splitting of a single fertilized egg into two or more embryos.

Cleavage can occur more than once, resulting in monozygotic triplets or even a rare set of monozygotic quintuplets. Completely monozygotic quintuplets are rare – so unusual that it is difficult to even estimate the likelihood of their occurrence. Quintuplets can be all male, all female, or a combination of both, but monozygotic quintuplets will always be of the same sex because they come from the same fertilized egg. Most fives are a mixture of boys and girls; all male or all female fives are rare. The first female quintuplets were born in the USA in 20153.