Multiple Births

Identical Twins Mono zygotic Formed from 1 sperm and 1 egg The zygote splits into 2 Always the same gender

Fraternal Twins Di zygotic twins Formed from two sperm and two eggs Could be 2 boys or 2 girls or one of each

Twin Statistics 3% of births are twin births 23/1,000 Fraternal Twin 4/1,000 Identical Twins

Conjoined Twins Identical twins who did not completely separate during the zygote stage Surgery to separate conjoined twins depends on the extent of sharing vital organs Occurs in about 1 in 50,000 human pregnancies

Conjoined Twins: Abigail and Brittany Hensel Born conjoined in 1990 Today, they are 24 years old and school teachers

How higher order multiples are formed: Identical: Identical triplets occur in almost the same way as identical twins, but instead of the egg dividing once, one of those halves divides again to create three genetically identical babies. In the rare cases of identical quads, both halves would divide to form 4 identical babies. The Dionne quints of Canada were identical quintuplets, the only set in the world. Fraternal: Fraternal triplets would occur if three eggs were released by the mother and each fertilized by a different sperm. The same would occur for fraternal quads if 4 eggs were released and fertilized, as well as 5 being released for quints. The chances of having spontaneous (not from IVF or fertility drugs) quads and quints isn’t as common, spontaneous quints are quite rare, fraternal or otherwise. Mixed: Higher multiples can often be a combination of identical and fraternal. The most common type of spontaneously conceived triplets are “a pair and a spare”, two identical and one fraternal. Two eggs would be released by the mother and fertilized, and only one would split to form identical twins. This can occur with quadruplets, you could have 2 identical and 2 fraternal (three eggs released, one splits, this seems to be the most common of all fraternal), 2 sets of identical twins (2 eggs released, both split), or 3 identical and 1 fraternal (2 eggs released, one splits once, and then again). The same can happen with quintuplets, you could have 2 identical, 3 fraternal (which seems to be the most common of all fraternal), or any combination of identical and fraternal, although it is very rare to see more than 2 identical in a set of quints. Combinations for sextuplets and higher would be similar, although it is highly unlikely to see identicals in sextuplets and higher since almost all of them come from fertility drugs. (Although there was one case where the sextuplets were 3 identical and 3 fraternal).

Triplets (3) Formed the same way as twins Can be identical or fraternal

Quadruplets (4)

Quintuplets (5)

Sextuplets (6)

Septuplets (7)

Octuplets (8) Chukwu Octuplets (8 born, 1 death) Born in 1998 in Houston, Texas Suleman Octuplets Born in 2009 in Bellflower, California