Miscarriage happens when a pregnancy stops growing. Eventually, the pregnancy tissue will pass out of the body. Some women will feel crampy, period-like pain and in most cases there will be vaginal bleeding.

Miscarriage is very common in the first few weeks of pregnancy. Studies show that up to one in five women, who know they are pregnant, will have a miscarriage before 20 weeks. Mostly this will happen in the first 12 weeks. The actual rate of miscarriage is even higher because some women have very early miscarriages without ever realising that they were pregnant.

When women miscarry three or more times, tests can be done to look for a cause. Testing is not usually offered to women who miscarry once or twice because it is very unlikely that anything would be found. 

What causes a miscarriage?

Usually no treatable cause is found for a miscarriage. Research tells us that about half of all miscarriages happen because the chromosomes in the embryo are abnormal and the pregnancy doesn’t develop properly from the start. In this case, miscarriage is nature’s way of dealing with an abnormal embryo. Nothing can be done to prevent miscarriage from occurring if a pregnancy is developing abnormally.

  • Miscarriages are more common in older women than younger women, largely because chromosomal abnormalities are more common with increasing age.
  • Miscarriages are also more common in women who smoke and in women who drink more than three alcoholic drinks per week in the first 12 weeks of pregnancy. Research suggests that miscarriage is also more common in women who drink more than 500mg of caffeine per day; this is about three to five cups of coffee.
  • Some medical conditions in the mother, such as uncontrolled diabetes, fibroids or thyroid problems, can lead to miscarriage. Rare medical conditions which affect blood clotting can also cause miscarriage. Women who have three or more miscarriages in a row should be checked for these conditions.
  • Early tests in pregnancy, such as chorionic villus sampling (CVS) and amniocentesis, carry a small risk of miscarriage. These are tests where a needle is inserted into the uterus.
  • High fever may lead to miscarriage, but minor infections (such as colds) are not harmful. 

Preventing miscarriage

Miscarriages happen to even the healthiest of women; nevertheless, being healthy will increase your chances of a healthy pregnancy. The best that you can do is follow the advice for a healthy pregnancy:

  • don’t smoke
  • modify your caffeine intake
  • avoid alcohol
  • where possible, avoid contact with others who have a serious infectious illness.

If you have previously had a miscarriage, your next pregnancy is likely to be normal. If you have had three miscarriages in a row further tests are recommended. 

Diagnosing a miscarriage

Women seek medical care at different stages of a miscarriage; sometimes the miscarriage has already happened and sometimes it has only just begun. To confirm that you have had or are having a miscarriage the doctor will look at a number of things, including:

  • your symptoms – such as pain and bleeding
  • examination findings
  • ultrasound and blood tests.

After examination, your doctor can usually tell you if your miscarriage is ‘complete’, ‘incomplete’ or ‘missed’.

  • a miscarriage is complete when all the pregnancy tissue has passed
  • a miscarriage is incomplete when some of the pregnancy tissue has passed, but some is still inside the uterus
  • a ‘missed’ miscarriage is when the pregnancy has stopped growing but the tissue has not passed and there is still a sac (the structure surrounding the embryo or fetus) in the uterus. 


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