Miscarriage refers to the premature end of a pregnancy before the developing baby is able to survive outside the uterus. Miscarriage can occur during the first or second trimester, before 20 weeks. Most occur in the first 12 weeks of pregnancy. They often are unexpected and isolated events. About 15%-20% of recognized pregnancies end this way.

Fetus in First Trimester
Nucleus image
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Miscarriages often occur for the following reasons:

  • Chromosomal abnormalities (common cause)
  • Abnormalities in the uterine tract, such as fibroids
  • Hormonal problems, such as not having enough progesterone, a female hormone needed to support pregnancy
  • Factors related to the immune system, such as blood-clotting problems or rejection of the fetus
  • Trauma

In some cases, the cause of miscarriage is unknown.