vitamin D deficiency in pregnancy

Last edited 03/2021 and last reviewed 04/2021

Vitamin D deficiency in Pregnancy

For routine supplementation, current guidance recommends 10mcg (400units) daily in all pregnant women and most antenatal vitamins contain this dose of vitamin D.

Guidance suggests that specialist advice should be sought if vitamin D deficiency in pregnancy (1,2,3).

  • a re-emergence of rickets has been seen in the UK, with cases mainly affecting children from ethnic minorities; this is probably related to both maternal and infant diet and lifestyle in particular groups (for example, in women who cover their skin)

  • women should have adequate vitamin D stores for their own requirements, for their developing fetus and to build stores for early infancy particularly if they plan to breast-feed

  • during pregnancy, maternal vitamin D deficiency (defined here as less than 30nmol/L) can lead to deficiency in the infant (2)

  • testing:
    • no consensus on exactly which pregnant women to test for vitamin D deficiency (or what the optimal levels should be in pregnancy) but there is an argument that some groups of women who are pregnant should have screening test: for example, on the basis of skin colour or obesity. If a pregnant woman is tested for deficiency and found to be deficient, then the deficiency should be corrected (2)

  • safety:
    • vitamin D use in human pregnancy is not associated with an increased risk of congenital malformation, although the data are insufficient to confirm that there is unequivocally no risk (2)
      • bolus injections or oral doses of more than 10,000units per day should be avoided and very high single bolus doses (i.e. 300,000 - 500,000units) should not be used in pregnancy. Safety data relate to use in the second or third trimesters and use of high dose vitamin D in the first trimester is therefore usually avoided

  • dose for correction of deficiency
    • Correction should begin in the 2nd or 3rd trimester because of the lack of safety or outcome data in first trimester, and because the majority of skeletal growth and development is thought to occur in the 2nd or 3rd trimester.
      • what constitutes an adequate level in pregnancy is still controversial and many suggest >50 nmol/L to be adequate whilst some suggest >75nmol/L; with deficiency being represented by a serum 25OHD level of <25-30nmol/L.Current DoH guidance makes recommendations in relation to routine supplementation in pregnancy and breastfeeding but does not address the issue of correction of vitamin D deficiency in these situations (2)
      • American College of Obstetricians and Gynaecologists (ACOG) guidelines state:
        • "For the individual pregnant woman thought to be at increased risk of vitamin D deficiency, the serum concentration of 25-OH-D can be used as an indicator of nutritional vitamin D status. Although there is no consensus on an optimal level to maintain overall health, most agree that a serum level of at least 20 ng/mL (50 nmol/L) is needed to avoid bone problems.. Based on observations of biomarkers of vitamin D activity, such as parathyroid hormone, calcium absorption, and bone mineral density, some experts have suggested that vitamin D deficiency should be defined as circulating 25-OH-D levels less than 32 ng/mL (80 nmol/L)"

      • optimal dose to correct vitamin D deficiency safely in pregnancy is not still clear from the available data (2)

      • Seek expert advice before starting a regimen to correct vitamin D deficiency in pregnancy:
        • First trimester correction of vitamin D deficiency (5)
          • there is a lack of safety or outcome data for correcting vitamin D deficiency in the first trimester

        • Second or third trimester correction of vitamin D deficiency (5)
  • dose for rapid correction:
    • no consensus on what constitutes a very low vitamin D level, but a level of less than 15nmol/L, for example, would be considered as being very low by most clinicians. If the baseline vitamin D level is very low and the woman is in the 3rd trimester of her pregnancy, then rapid correction may be required particularly if there are unmodifiable risk factors
      • in these cases it would be rational to use doses higher than 4000units/day (but not more than 10,000units/day) (2)
        • examples of doses which might be used for rapid correction are 7000units/day for 6-7 weeks or 10,000units/day for 4-5 weeks to provide a cumulative dose of around 300,000units. In some cases, it might also be reasonable to use a weekly dose of 20,000 units per week as the Royal College of Obstetricians and Gynaecologists suggests, although it should be noted that the evidence base for this recommendation is unclear. Higher doses are usually used with the input of an obstetrician and ideally with monitoring of calcium levels

  • other factors:
    • when choosing a regimen, prescribers should also take into account:
      • severity of deficiency at baseline,
      • whether modifiable risk factors (such as covering of the skin for religious/cultural reasons) remain an issue,
      • likelihood of compliance,
      • time of year,
      • planned holidays in the sun and
      • product availability

  • products:
    • Preferred forms of vitamin D used for treating vitamin D deficiency (5)
    • products containing vitamin A (such as Cod Liver Oil) should be avoided because this is a known teratogen

  • monitoring:
    • to avoid maternal (and possibly fetal or neonatal) hypercalcaemia (2),
      • has been suggested that pregnant women being treated for vitamin D deficiency (taking doses of >2000units per day or equivalent) should have their serum calcium levels checked a month after completing the treatment dose regimen
        • calcium levels should be checked again three months later when steady state vitamin D levels have been achieved
        • subsequent monitoring of calcium levels depends on duration of treatment and concerns about toxicity. If calcium levels are raised, then the prescriber should review the prescription for vitamin D or reduce the dose
        • routine monitoring of vitamin D levels is not necessary. If vitamin D levels are checked too soon after starting treatment, levels could be falsely low because it takes around 3 months after completing the treatment dose regimen for steady-state levels to be reached

  • calcium intake:
    • pregnant women should try to maintain an adequate calcium intake (700mg/day) through their diet. Calcium calculators (e.g. http://www.rheum.med.ed.ac.uk/calcium-calculator.php) are available to help estimate patients dietary calcium consumption

  • combined calcium and vitamin D products should not routinely be used to correct vitamin D deficiency in pregnancy. There may be a role for combined use of vitamin D and calcium in women at high risk of pre-eclampsia (4,5)

Reference:

Related pages:

vitamin D deficiency

vitamin D in pregnancy