In the UK, miscarriage is defined as the loss of a pregnancy before 24 weeks and sadly, it can affect one in four people who are pregnant. The cause of miscarriage is often unknown, but here we’ll explore some of the common known causes of miscarriage.

Causes of miscarriage

It’s not always possible for doctors to find out what has caused a miscarriage and frustratingly, it can be difficult to access any tests unless you’ve experienced three or more miscarriages. But here’s what we do know: 

Chromosome abnormalities

About half of early miscarriages are caused by chromosome abnormalities or genetic faults which happen by chance. We don’t know what causes these faults, but we do know that if your miscarriage was caused by a genetic fault, chances are your next pregnancy will be healthy. 

Lifestyle factors

We know that there are some lifestyle factors that can increase the risk of having a miscarriage. There are things you can do to try to reduce this risk, which include:

  • Not smoking
  • Not drinking or using drugs during pregnancy
  • Maintaining a healthy weight
  • Limiting caffeine intake

Low levels of progesterone

The hormone progesterone is needed to support a healthy pregnancy and some miscarriages are caused by low levels of progesterone. Recent research has shown that for some people, a progesterone supplement can reduce the risk of future miscarriages. 

Antiphospholipid syndrome (APS)

APS is a blood clotting disorder that causes problems in the placenta which can lead to pregnancy loss. A blood test can check if you have APS, and it can be treated with a low dose of aspirin if trying to conceive in the future.

Thyroid abnormalities

The thyroid gland is responsible for maintaining your metabolism and body growth. When your thyroid gland is underactive this can impact the fertilisation of an egg to form an embryo, which in turn can increase the risk of miscarrying. 

Infections during pregnancy

Most mild infections like a cough or cold are not harmful during pregnancy, however, certain illnesses like sexually transmitted infections or food poisoning can increase the risk of miscarriage. Similarly, influenza or Covid-19 can also increase the risk of miscarriage. 

Support after a miscarriage

If you have had a miscarriage, it’s natural to worry that you’ll have another if you get pregnant again. Most miscarriages are random, one-off occurrences and most people who have had a miscarriage will go on to have a healthy pregnancy. Every pregnancy loss is different, and there’s no right or wrong way to feel about it. If you’re struggling with your feelings, you may need some support. Please read our article Support during and after a miscarriage.