The importance of the neural tube and folic acid

As you enter week 5 of your pregnancy you can be assured that although your baby is only fractionally larger than a sesame seed, its growth and development are taking place at an incredibly rapid rate.

Important landmarks at this stage include the emergence of the child’s facial features, the first pumping of the tiny heart, and the “budding” of your child’s arms and legs. Soon your child will begin to look less like a tadpole and more like what it is – a miniature, emerging human.

The importance of the neural tube

The neural tube is a hollow structure of tissue which later develops into the brain, spinal cord and nervous system. At week 5, the neural tube begins to close, forging the way for communication between spine and brain. There are four stages of neural tube subdivisions that occur in the creation of the nervous system. These take place in the prosencephalon, the mesencephalon, the rhombencephalon, and the spinal cord. Once these have all been achieved your baby will have a brain, a spine, and a spinal cord.

Neural tube defects

If there are problems with the development of the neural tube, this can result in defects affecting the brain, spine, or spinal cord. The majority of these occur during the first four or five weeks of pregnancy and may be very serious or even life-threatening. The following are the most common neural tube defects:

• Spina bifida – occurs as a result of a fault in the spinal cord and surrounding bones leaving a gap in the spine. Spina bifida literally means “split spine”.
• Anencephaly – a defect in which the baby is born with portions missing from its brain and/or skull
• Occult spinal dysraphism – describes a group of congenital and pathological changes affecting the development of the spine and spinal cord
• Encephalocele – also known as cranium bifidum, this condition results in protrusions of the brain and its membranes through openings in the skull

Risk

If you, your partner, or a member of either of your families has a neural defect, you are likely to be at increased risk of having a child with the same or a related condition. Additionally, you are at increased risk if you have previously had a child with a neural defect, are obese, or if you suffer from insulin dependent diabetes. Another notable risk factor is if you take anti-epileptic medications, particularly those that contain valproic acid or sodium valproate.

However, even if you have a family history of neural tube defects or are affected by other risk factors, the chance of having a child with some form of neural tube defect remains relatively low, while for general members of the population, the risk of such a defect stands at less than one in 1,000.

About two-thirds of neural tube defects can be prevented if you eat enough folate (folic acid) before and during the first three months of pregnancy.

Detection

In some cases neural tube defects may be detected during your routine ultrasound scan at around 12 weeks. However, they are more likely to be evident later on in your pregnancy, so are more likely to be detected during your mid-pregnancy anomaly scan which typically takes place between week 18 and week 21 of your pregnancy. Although not all neural tube defects are detected by the anomaly scan, most are – for example, around 9 in 10 cases of spina bifida are detected.

Occasionally you may need the anomaly scan to be repeated, either because the scan does not present a clear enough picture of your baby’s health or because the sonographer believes it is in your best interests to be referred to a specialist.

The benefits of folic acid

It is accepted by most agencies that folic acid (also called vitamin B9 as well as “folate” when in its non-synthesised state) can significantly reduce a woman’s chances of having a child with a neural tube defect.

In fact, the Department of Health recommends that women who are trying to become pregnant should take a daily supplement of 400 micrograms of folic acid and, once pregnant, should continue on this dosage for 12 weeks.

Women at increased risk of having a child with a neural tube defect should take a slightly higher dose of folic acid: 500 micrograms daily.

It is fine if you have become pregnant without taking folic acid in the pre-conception period – just begin to take it once you are pregnant.

Although there are no official guidelines recommending that mothers-to-be continue to take folic acid, throughout the whole pregnancy, there is not thought to be any harm in continuing to take a B9 supplement.

It is advisable that all women of child-bearing age take a folic acid supplement just in case they become unexpectedly pregnant.