Miscarriage is the most common pregnancy loss affecting 1 in 4 pregnancies. Most miscarriages happen in the first 12 or 13 weeks of pregnancy  and it is much less common to miscarry after this stage. 

The main causes of early or late miscarriage are thought to be: 

• Chromosome problems: These are usually one-off events, happening out of the blue, but they might be due to a problem that you or your partner have, probably without knowing. Examples of chromosome arrangements or differences that can cause miscarriage are Downs Syndrome, Edwards Syndrome and Turners Syndrome. 
• Genetic: This is when the baby doesn’t develop normally right from the start and cannot survive.  This is the cause of more than half of all early miscarriages, but it can cause late loss too. 
• Structural: Problems in the baby’s body, for example spina bifida or a congenital heart defect. 
• Antiphospholipid Syndrome (APS): APS is a condition that increases blood-clotting. If blood clots too easily during pregnancy, it can cause early or late miscarriage, as well as other pregnancy problems. 
• Infection: Some infections can cause a late miscarriage, either by infecting the baby or by infecting the amniotic fluid (the liquid around the baby). 
• Anatomical: There are two main anatomical causes of late miscarriage: 
  • An unusually shaped womb (uterus), especially one that is partly divided in two. 
  • A weak cervix (the neck of the womb), which may start to open as the uterus becomes heavier in later pregnancy and thus cause a miscarriage.