It is really important to understand that in most cases, we just don’t know why miscarriage occurs, and it is unlikely that you have done something to cause a miscarriage.
At a glance
- Around 50-80% of miscarriages result from random chromosomal abnormalities
- There are many factors that can increase the risk of miscarriage and they can be categorised into age, previous miscarriage(s), genetics, lifestyle, and health and medical
- We answer some common questions about risk factors.
- You can download our printable Why Have I Had a Miscarriage? Fact Sheet.
Research tells us that around 50-80% of miscarriages result from random chromosomal abnormalities, which occur more frequently in the sperm and eggs of people over the age of 35. Women who experience miscarriage due to a random chromosomal abnormality have a high chance of a later healthy pregnancy.
Below are things we know to increase your risk of miscarriage. Your doctor or healthcare provider will be able to provide you with advice based on your circumstances. While these things increase the risk of miscarriage, every person is different, and these factors may affect you differently depending on your circumstances.
Age
The older the person who is pregnant, the higher the risk of miscarriage due to decreased egg quality with age. Additionally, the older your partner/person donating the sperm is, the higher the risk of miscarriage. For women and men, the risk of miscarriage increases significantly after age 35 and more so after age 40.
Previous miscarriage(s)
Most women will have a successful pregnancy after 1 or 2 early non-consecutive miscarriages (as long as no specific cause is found). The chance of having another miscarriage does increase slightly after two consecutive miscarriages and considerably after three or more consecutive miscarriages. The risk also depends on other factors such as age, genetics, lifestyle, health, and medical factors.
Genetics
Around 50-80% of miscarriages are due to chromosomal abnormalities. The vast majority are due to spontaneous chromosomal abnormalities in the parent sperm or egg, and only a small number to hereditary abnormalities. Chromosomes are tiny structures inside the body’s cells that carry many genes, the basic units of heredity. Genes determine a person’s physical characteristics.
The older you and your partner are, the higher the risk of abnormalities. If you have experienced recurrent miscarriage, your doctor or specialist may refer you and your partner to a genetic counsellor. You can discuss and test for potential genetic risks or abnormal foetal developments (heart defects, chromosomal abnormalities, spina bifida).
Finding out that you have experienced miscarriage due to genetic reasons can be very distressing. A genetic counsellor can help you assess your risk of genetic disorders and how you might move forward with future pregnancies.
Lifestyle
Smoking, alcohol, and drugs
Smoking during pregnancy is associated with an increased risk. It is recommended that you and your partner quit smoking before trying to conceive.
Alcohol consumption during pregnancy is also associated with an increased risk of miscarriage. It is recommended that you don’t drink alcohol during your pregnancy or when trying to conceive. Using certain drugs by either parent may also increase the risk of miscarriage.
It was a really feeling of ‘What the hell?’ kind of thing. Where is this coming from and . . .what have we done wrong? Have we drunk too much alcohol?
Being exposed to environmental factors
Exposure to certain pesticides, air pollution, and other harmful substances by either parent may increase the risk of miscarriage.
Bodyweight
Obesity or being significantly underweight are associated with an increased risk of miscarriage. A BMI under 18 is considered underweight. Obesity is a BMI over 30.
High caffeine consumption
Pregnant women are recommended not to consume more than 200mg of caffeine daily. It’s in coffee, tea, caffeinated drinks, and chocolate. High levels of caffeine consumption have been linked with pregnancy complications, including miscarriage. 200mg a day is around 2 cups of instant coffee. Tommy’s in the UK has developed a caffeine calculator to help determine how much caffeine you have daily.
Stress
Stress is a normal part of life. However, excessive stress for prolonged periods is not suitable for your health at any time. If you experience prolonged high stress, speak to your doctor about ways to help.
Health and Medical
There are a number of health and medical conditions that your doctor or specialist might test you for to find out why you have miscarried. In Australia, testing for the cause of miscarriage is not generally offered unless you have experienced recurrent miscarriage. Our testing to find out why my miscarriage occurred section discusses these conditions in more detail.
Could this have caused my miscarriage?
Exercise
Moderate exercise during pregnancy is recommended both for the health of the baby and you. Your doctor or Specialist can advise about safe practices during pregnancy.
Having sex
Sex is safe during pregnancy unless advised otherwise by your doctor or specialist.
Eating spicy food
Most foods are safe to eat during pregnancy. Eating spicy food does not cause miscarriage. Your doctor or specialist may advise you about avoiding certain foods such as raw foods and raw dairy products. These foods could lead to bacterial infections.
Lifting something
It’s best to avoid heavy lifting during exercise and pregnancy in general, particularly if you have certain pregnancy complications. Lifting things in general though does not cause miscarriage. There can be risks for example, if you have placenta previa, where you do need to avoid lifting as it can increase your risk of bleeding or worse. Placenta previa itself is not caused by lifting, though.
Being over-tired
It’s quite common to feel tired during pregnancy. Overall wellness is essential when you are pregnant, and getting enough sleep and proper rest is important during this time. Being over-tired in pregnancy does not cause miscarriage.
It runs in the family
Most miscarriages are due to random chromosomal abnormalities and just because someone in your immediate family experienced a miscarriage, it doesn’t mean that you will too. However, if you know about a familial history of chromosomal abnormalities, you can discuss this with a medical professional before you start trying for a baby.
