Most miscarriages happen in the first 12 or 13 weeks of pregnancy. It is much less common to miscarry after this stage.
What is a late miscarriage?
Late miscarriage, also called second-trimester or mid-trimester loss, refers to a miscarriage that happens when a baby dies between 14 and 24 weeks of pregnancy.
If a baby dies before 14 weeks but the miscarriage itself happens later, that is usually considered to be a missed or silent first-trimester loss.
If a baby dies at or after 24 weeks of pregnancy, this is called a stillbirth.
(These definitions apply to the UK – they can differ in other countries.)
You may find it very hard to understand why a very late loss is called a miscarriage rather than a stillbirth. The reason is that 24 weeks of pregnancy is the legal age of viability in the UK – the stage at which a baby is thought to stand a good chance of surviving if born alive. Some parents find this distinction very upsetting.
Why do late miscarriages happen?
There are several known causes of late miscarriage. Some can cause earlier losses too, while others can cause problems after 24 weeks of pregnancy as well as before. Most miscarriages at whatever stage happen because of an abnormality in the baby.
Causes of late miscarriage
The main causes of late miscarriage are thought to be:
- Chromosome problems: These are usually one-off abnormalities, 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 problems 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.