pregnant woman
Anne Ackermann/Digital Vision/
Getty Images

About 15 to 20 percent of recognized pregnancies end in miscarriage.
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 [source: American Pregnancy Association].

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 [source: APA].

In the next section, we'll explore the most common factors known to increase the risk of miscarriage.

Video Gallery: Pregnancy Technology
Sequenom is developing a new, noninvasive technique for detecting genetic defects as early as the first trimester of pregnancy. See how DNA and genetics work in this video from MultiVu.

In November 2007, healthy quintuplets were born in the United Kingdom for the first time in 10 years. Most quintuplet pregnancies have severe complications and often result in premature births or­ worse.

The infant mortality rate has skyrocketed in parts of Indonesia since the 2004 tsunami. See how midwives are helping to curb infant deaths in this video from UNICEF. ­

­