When a woman is pregnant with fraternal twins, this means that two eggs have become fertilized and attached in the uterine wall. This is different from identical twins because they are produced when one egg produces two babies by splitting in two.
Many women do not realize that they are pregnant with twins until an ultrasound can be completed or the heartbeats can be heard. However, some women have ultrasounds from the very beginning of their pregnancy, which may show that they are pregnant with twins sooner.
Vanishing twin syndrome occurs when one of the twins is miscarried. However, instead of passing the tissue, the second twin will actually absorb the tissue. Doctors can then examine the placenta after the baby has been born to determine if there was indeed a second twin.
This syndrome is very common and many women do not even realize it has occurred. However, for those who have an early ultrasound, they may find that two heartbeats are discovered during one ultrasound, but only one the next. Also, some women may have some symptoms similar to a miscarriage. This is a sign of vanishing twin syndrome and occurs in nearly 30% of all twin pregnancies.