Miscarriage is in fact the definition for pregnancy loss before 20 weeks gestation. After the 20 week mark, pregnancy loss would be defined as a still birth. The risks do go down drastically after the first trimester. Even within the first trimester itself, you are less likely to miscarry with every passing week. By the time you have reached your second trimester, though there are no guarantees that you will not have a miscarriage, the odds are very much in your favor. What causes miscarriages, then? First trimester miscarriages are largely due to chromosomal abnormalities, according to research done on miscarried fetuses. Pregnancies that have chromosomal anomalies are claimed to have a miscarriage rate of as high as 95 percent. Progesterone deficiencies and luteal phases that are too short to allow implantation of a fertilized egg to be completed are also possible causes of first trimester miscarriages.
Second trimester miscarriages are more likely to be caused by cervical or uterine problems, or fibroids in the uterus. While there are risk factors for miscarriage, most miscarriage occur entirely by chance. Miscarriage is much more common than most people know, and it is a normal part of the reproductive process. Miscarriages are more common in first pregnancies than in subsequent pregnancies, and the vast majority of women who had one miscarriage have no problems conceiving again, and going on to have healthy babies.