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

Fetus in First Trimester
Nucleus image
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Some miscarriages cannot be explained. Miscarriages often occur for the following reasons:

  • Chromosomal abnormality (most common cause)
  • Advanced maternal age
  • Uterine defects
  • Fibroids
  • Scar tissue from a past surgery
  • Insufficient progesterone (a female hormone needed to support pregnancy)
  • Infection in the genital tract
  • Immunologic factors that may cause blood-clotting problems or rejection of the fetus