Miscarriage (also called early pregnancy loss) is when a baby dies in the womb (uterus) before 20 weeks of pregnancy. For women who know they’re pregnant, about 10 to 15 in 100 pregnancies (10 to 15 percent) end in miscarriage. Most miscarriages happen in the first trimester before the 12th week of pregnancy. Implantation bleeding is an early sign of pregnancy that, when identified, rules out complications like an ecoptic pregnancy or miscarriage. It's light, stops on its own, and usually goes away within a day or two — if it's as long as your period, it's not implantation bleeding. Not everyone experiences it, and if you don't, it doesn't mean anything about your pregnancy. A blighted ovum, also known as an anembryonic pregnancy, occurs when something goes wrong shortly after conception. After an egg is fertilized and implants in the uterus, it begins to develop a placenta but not an embryo. In a normal pregnancy, a sperm fertilizes an egg shortly after ovulation. Within hours, this fertilized egg starts dividing. Unsuccessful implantation is just one reason you might not get pregnant during what you’d hoped would be a successful cycle. Here are the most common reasons an embryo doesn’t implant: Advanced maternal age Chromosomal abnormalities Genetic factors Poor embryo quality Unexplained failures What does this mean for you?. The period of implantation of the embryos in the female uterus consists of several phases: detachment of the zona pellucida, pre-contact and apposition, adhesion and invasion. In the following image we can see the stages of implementation, although we explain them in detail below. Implantation process Detachment of the zona pellucida.