Can doctors tell if twins are identical or fraternal?
Most think that fraternal twins have two placentas and identical twins share one placenta, but this is not necessarily the case. One-third of identical twins separate within a few days of conception, before the placental tissue has begun to form. Each embryo then grows it’s own placenta. So if your doctor said that you and your twin were fraternal because you had two placentas, the doctor may be incorrect. Though fraternal twins have their own separate placentas, sometimes the two fertilized eggs implant close to each other in the uterus, which can result in their placentas fusing. The two fused placentas look like one placenta, causing them to be mistaken for identical twins. This is a fairly common mistake; as many as twenty percent of all twin births are misidentified as identical or fraternal. This confusion is one reason why we take special steps, such as sometimes taking blood, to determine if twins are identical or fraternal.
