Identical of fraternal?

If you’ve got twins or triplets or more this will be common knowledge to you by now, but for those not so well versed in the world of multiples (this was me when we first found out we were having twins) this can be a confusing question.

Identical or Fraternal? What is the difference?

• Fraternal Twins, non Identical twins or dizygotic (meaning two eggs) twins occur when two (or more but then of course they would be triplets or more) separate eggs are fertilised by separate sperm. This can happen spontaneously with double ovulation (a tendency that is thought to be passed on genetically in some families) or through a variety of assisted conception methods such as IVF.  Fraternal twins share the same genetic similarities as any non-twin siblings which is why they may look some what alike or completely different and even be different sexes.

• Identical twins or monozygotic (meaning one egg) twins occur when a single egg is fertilised by a single sperm and then splits creating two genetically identical babies. The split happens sometime within the first two weeks after conception. The later the egg splits the ‘more identical’ the twins are said to be, really late splits  can result in conjoined twins.  It is not known why the egg splits and identical twins are thought to be a random occurrence.

So that is the technical stuff… here are some common misunderstandings…

• If the twins are a boy and a girl they must be fraternal… identical twins are always the same sex.

• Just because some twins look very very alike doesn’t mean they are identical twins.

• Just because some twins have some differences in appearance doesn’t mean they are not identical.

• All fraternal twins have separate placentas. Some identical twins have separate placentas and some identical twins share a single placenta.

• Triplets, Quads and more can be a combination of both fraternal and identical twinning – ie triplets that are made up of a pair of identical ‘twins’ and a fraternal ‘twin’

And how do you know if your twins are fraternal or identical? I’ll get to that later!

Kate blogs about life with twins plus one at picklebums