The anembryonic pregnancy or “blighted ovum” is a specific type of miscarriage in which the fertilized egg implants in the uterus but the embryo does not develop. It is a relatively common problem: 10-15% of clinically detected pregnancies are lost spontaneously and one third of them are blighted ovum.
After fertilization, that is, after the union of sperm and egg, begin a series of cell divisions that lead to the formation of the gestational sac  surrounded by a “shell” or cover called trophoblast (which is the one that will lead to future placenta); inside the gestational sac the embryo will develop. In the case of anembryonic pregnancy the gestational sac is formed with the trophoblastic cover but the embryo is not displayed because it has stopped developing at a very early stage, before reaching a millimeter in size, so it cannot be detected with an ultrasound. […]