The moment you find out you’re pregnant is a life changing one. You and your partner will begin preparing for your baby from that moment forward. You’ll set up a nursery, set aside funds and start buying baby clothes. You’ll have an entire life ready for a new baby, so when you find out you’re having two, your world will be flipped upside down. Twins can certainly be a blessing, but they will also require a lot of extra preparations. To better prepare for their twins, some women choose to find out in advance whether their twins will be fraternal or identical.

Identical twins are those that look exactly the same. This happens because a single egg splits in two to create two separate fetuses. Fraternal twins are born from two separate eggs that happened to be fertilized at the same time.

To find out whether you are having fraternal twins or identical twins, there are numerous tests your health care provider can perform while they are still in the womb. In some cases, your doctor will be able to tell from a simple ultrasound. If the babies are a different gender, they are fraternal. If not, there still might be some question about their relationship, but it could also be clear if they are growing in two separate placentas. Women who want to find out but cannot do so from an ultrasound could also receive a chorionic villus sampling (CVS).

A chorionic villus sampling involves the removal of cells from the womb. There is some controversy surrounding the procedure, as some studies show that it has an association with miscarriages. However, a recent study shows that the procedure doesn’t actually have a high association with such negative side effects, so women who are interested in it shouldn’t be concerned.

If you are worried about receiving a CVS and cannot determine the nature of your twins from an ultrasound, you’ll have to wait until they begin to develop to find out whether they are fraternal or identical. If you notice any minor discrepancies at all in their appearance when they are babies, they are fraternal. It can be difficult to see these differences when your twins are still infants, so most people can’t determine their relationship until they become toddlers. Unless your twins come down with any serious genetic diseases, finding out whether they are fraternal or identical will simply satisfy your curiosity.

Source: K Aragwai et al: Pregnancy Loss After Chorionic Villus Sampling And Genetic Amniocentesis In Twin Pregnancies. Ultrasound in Obstetrics and Gynecology Volume 40 Issue 2 pp. 128-134 August 2012