Identical twins or fraternal twins? How do you know?

Identical twins come from the same egg that's been fertilised by a sperm and divided. Identical twins always have the same DNA and biological sex and are genetically alike. They can look very similar, but won't necessarily.

Fraternal twins come from two different eggs that have each been fertilised by their respective sperm. Fraternal twins have different DNA and aren't genetically alike so can have different sexes. Fraternal twins are no more alike than siblings. There are twice as many fraternal twins than identical twins.

It doesn't make any difference if twins come from one or two eggs. Many parents still want to know if their children are identical or fraternal twins, and there are ways to find out.

Four ways to find out if your twins are fraternal or identical:

1. Are the babies the same sex or different? If they're not the same sex they're fraternal twins.
2. Do the babies have the same placenta and sex? They might be identical twins but not definitely. Identical twins can also have different placentas. Sometimes it's possible to see whether there are one or two placentas during an early ultrasound or at birth, but not always. If you want to know for certain you can send the placenta for analysis.
   
3. Do the babies share an amniotic membrane, with no or only two thin membranes between them? Then they're identical twins. It may be possible to see the number of membranes during an ultrasound examination or childbirth.
4. Do your babies have the same DNA? Then they're identical twins. The most certain way to get answers is to do a DNA analysis. It costs around 2000 SEK and the parents pay for themselves. The sample is taken from the babies' mouths and you'll get an answer 4–6 weeks later.