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 your 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 still unclear how folic acid helps prevent spina bifida. It's likely that folic acid is needed for important biochemical reactions in the body.
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 significantly increased – from less than 1 in 1,500 to around 1 in 25.
If you have a family history of spina bifida, it's very important that you take high-dose folic acid, prescribed by your GP before you become pregnant, and for at least the first 12 weeks of pregnancy.
Taking certain medications during pregnancy has been linked to an increased risk of having a baby with spina bifida or other birth defects.
Valproate and carbamazepine are medications 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 medications if there's a chance you could get pregnant while taking them, but they may be needed if the alternatives aren't effective.
It's advisable to use a reliable form of contraception if you need to take one of these medications and aren't trying to get pregnant.
Tell your doctor if you're thinking about trying for a baby and you need to take one of these medications. 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 medication could affect your pregnancy, check with your doctor, midwife or pharmacist before taking it. Never stop taking a prescribed medication unless your GP or another healthcare professional responsible for your care advises you to.
Very rarely, spina bifida can occur 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 that can tell for certain if your baby has one of these genetic conditions.
Other risk factors for spina bifida include: