It's not known what causes spina bifida but a number of things can increase the risk of a baby developing the condition.

Not having enough folic acid during pregnancy is one of the most important factors that can increase your chances of having a child with spina bifida.

Folic acid (also known as vitamin B9) occurs naturally in some foods, such as broccoli, peas and brown rice. It's also added to foods, such as some breakfast cereals. Folic acid tablets are available from pharmacies and supermarkets, or a GP may be able to prescribe them for you. 

It's estimated that taking folic acid supplements before you conceive and while you're pregnant may prevent up to 7 out of 10 cases of neural tube defects, such as spina bifida.

It's not clear how folic acid helps prevent spina bifida. It's likely that folic acid is needed for important biochemical reactions in the body.

Read more about why you need folic acid in pregnancy.

Having a family member with a neural tube defect, such as spina bifida, increases your chances of having a baby with spina bifida.

If you've previously had a child with spina bifida, your chance of having other children with the condition is increased.

If you have a family history of spina bifida, it's very important that you take high-dose folic acid, prescribed by a GP before you become pregnant, and for at least the first 12 weeks of pregnancy.

Taking certain medicines during pregnancy has been linked to an increased risk of having a baby with spina bifida or other birth defects.

Valproate and carbamazepine are medicines linked to spina bifida. They're often used to treat epilepsy, and some mental health conditions, such as bipolar disorder.

Doctors will try to avoid prescribing these medicines if there's a chance you could get pregnant while taking them, but they may be needed if the alternatives are not effective.

It's advisable to use a reliable form of contraception if you need to take one of these medicines and are not trying to get pregnant.

Tell your doctor if you're thinking about trying for a baby and you need to take one of these medicines. They may be able to lower the dose and prescribe folic acid supplements at a higher than normal dose, to reduce the risk of problems.

If you're not sure whether a medicine could affect your pregnancy, check with your doctor, midwife or pharmacist before taking it. Never stop taking a prescribed medicine unless a GP or another healthcare professional responsible for your care advises you to.

Very rarely a baby can have spina bifida alongside a genetic condition such as Patau's syndrome, Edwards' syndrome or Down's syndrome.

If your baby is found to have spina bifida and it's thought they may also have one of these syndromes, you'll be offered a diagnostic test, such as amniocentesis or chorionic villus sampling. These tests can confirm if your baby has one of these genetic conditions. 

Other risk factors for spina bifida include:

• obesity – women who are obese (have a body mass index of 30 or more) are more likely to have a child with spina bifida than those of average weight
• diabetes – women with diabetes may have an increased risk of having a child with spina bifida