Written by Dr Amal Kehail
Evidence basis: Based on NICE guidance on antenatal care and on diabetes in pregnancy and on WHO antenatal care recommendations, which draw on published studies and expert consensus; general information that does not replace a consultation.
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Why folic acid is advised before pregnancy begins
Folic acid is the manufactured form of folate, a B vitamin found in food. Taken around conception, it lowers the chance of a neural tube defect, a problem in how the baby’s brain and spinal cord form. Spina bifida, where the bones of the spine do not close fully, is one example.
The neural tube forms and closes early, around the time a period is missed and often before a pregnancy test is positive. That is why folic acid is advised from before conception.
Folic acid lowers this chance but does not remove it. The anomaly scan in the middle of pregnancy looks at the baby’s spine and brain whether or not supplements were taken.
When to start folic acid, and when it can stop
The usual advice is to start a daily folic acid supplement when you stop contraception or begin trying for a baby, and to continue until about 12 weeks of pregnancy.
If you find you are pregnant and have not been taking folic acid, starting as soon as you know is still worthwhile up to about 12 weeks.
Advice about what comes after 12 weeks differs. NICE advises folic acid up to that point, because the neural tube has closed well before then. WHO recommends a daily iron and folic acid supplement throughout pregnancy, mainly to prevent anaemia. In practice many women move on to a pregnancy multivitamin, and the blood count usually guides whether extra iron is needed.
Side effects at the usual dose are uncommon. If the tablet makes nausea worse, taking it with food or in the evening can help; if it still disagrees with you, mention it rather than stopping quietly.
Who may be advised a higher dose of folic acid
Some women have a higher chance of a pregnancy affected by a neural tube defect, and for them a higher-dose tablet, started before conception, is usually advised. Examples include:
- diabetes, type 1 or type 2
- a previous pregnancy affected by a neural tube defect
- a neural tube defect in you, the baby’s father or a close relative
- taking some medicines for epilepsy
- sickle cell disease or thalassaemia
- a raised body mass index (BMI)
The list is not complete. Your doctor sets the dose and how long to take it, and with diabetes NICE also advises good blood glucose control before conceiving. If any of these applies to you, raise it before you start trying, because the standard strength sold without a prescription may not be enough.
Vitamin D in pregnancy, and why sunshine may not be enough
Vitamin D helps the body absorb calcium and phosphate, which the baby uses to build bones and teeth and which your own bones need too. Marked deficiency in pregnancy can lead to low calcium in the newborn and, later, soft bones (rickets).
Most vitamin D is made in the skin in sunlight, so a sunny climate might seem enough. In practice, levels are often low in women who have darker skin, keep most of their skin covered outdoors, spend most of the day indoors or in the car, or carry extra weight. Food adds little.
Guidance differs here too. NICE advises a daily vitamin D supplement for all women during pregnancy and breastfeeding. WHO does not recommend it routinely for every pregnant woman, because the benefit beyond correcting a deficiency is less certain; women found to have low levels can be given it.
A blood test may check your level, and if it is low a higher dose may be advised for a set period, in an amount your doctor decides. More is not better: large doses over a long time can raise blood calcium.
Food sources, and supplements to check before taking
Folate is found in green leafy vegetables such as spinach, and in broccoli, lentils, chickpeas, fava beans, oranges and breads or cereals with added folic acid. Vitamin D comes from oily fish such as salmon and sardines, egg yolks, red meat and foods with added vitamin D.
Some products need checking before you take them in pregnancy:
- Vitamin A as retinol: large amounts can harm the baby’s development. It is in some general multivitamins, fish liver oils such as cod liver oil and some hair and skin supplements, and liver and pâté are high in it.
- Medicines related to vitamin A, such as some acne treatments: avoided in pregnancy and ideally stopped before trying; ask about timing.
- Herbal and ‘natural’ remedies: most have not been studied in pregnancy, and their contents vary.
- Products that overlap, such as a pregnancy multivitamin plus separate vitamin D: together they can add up to more than intended.
Taking every supplement, or photos of the labels, to an antenatal check lets the doses be added up.