What Causes Miscarriage?

Miscarriages are common and can be caused by many things. In fact, almost 20% of known pregnancies result in miscarriage, and an even higher percentage of unknown pregnancies. Despite this, miscarriage is rarely spoken about, so people do not realise how common it is.

In the first trimester, between 50% and 70% of miscarriages are thought to be the result of chromosomal abnormalities. What this means is that either the egg or the sperm has the wrong number of chromosomes and so the fertilised egg cannot develop normally.

Additional causes of miscarriage in the first trimester include:

  • The fertilised egg failing to implant in the lining of the uterus
  • The embryo having structural defects
  • The woman’s immune system rejecting the embryo as a foreign body

Although miscarriage in the second trimester is less common, it does happen. Reasons for late stage miscarriages (occurring between 14 and 24 weeks’ gestation) include:

  • Increases in blood-clotting, a condition known as Antiphospholipid Syndrome (APS)
  • Infections of the baby or amniotic fluid
  • An unusually shaped uterus or weak cervix, which may start to open as the uterus becomes heavier

Miscarriages that take place after 24 weeks’ gestation are known as stillbirths.


  • https://www.babycenter.com/0_miscarriage-signs-causes-and-treatment_252.bc
  • https://www.sciencedaily.com/releases/2012/06/120607142244.htm

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