How Miscarriage Works

A miscarriage -- a pregnancy that ends spontaneously before the fetus can survive -- is an often devastating event. About 15 to 20 percent of recognized pregnancies end in miscarriage, but almost 75 percent of those are attributed to chemical pregnancy. This type of miscarriage occurs very soon after the egg has implanted into the uterus. It can go unnoticed because the resulting bleeding often occurs at the time of a woman's period, and she may not realize she had been pregnant at all.

Miscarriages usually occur within the first 13 weeks of pregnancy. While the chance of a miscarriage in all pregnancies is approximately 15 to 20 percent, studies show that once a fetal heart function has been noted, the chance of miscarriage falls to less than 5 percent [source: MedicineNet]. Unfortunately, the miscarriage rate can change with the mother's health and age. Women between 35 and 45 have a 20 to 35 percent chance of a miscarriage, while women over the age of 45 have a 50 percent chance. Having a miscarriage also increases your chance of having another, but only slightly. A woman under 35 who has had one previous miscarriage carries a 25 percent chance of having another one.