What do systematic reviews say?

Vitamin D plus calcium vs placebo or no intervention

It is very uncertain whether vitamin D + calcium supplementation changes low birthweight (less than 2500 g) compared with placebo or no intervention (very low certainty).

• Vitamin D supplementation for women during pregnancy 2019 · Cochrane Headline outcomes only
  RR 0.68 [0.1, 4.55]
  2 studies · 110 participants
  Very low

Vitamin D + calcium + other vitamins and minerals vs calcium + other vitamins and minerals (but no vitamin D)

Vitamin D + calcium + other vitamins and minerals showed no clear difference in low birthweight (less than 2500 g) compared with calcium + other vitamins and minerals (but no vitamin D) (low certainty).

• Vitamin D supplementation for women during pregnancy 2019 · Cochrane Headline outcomes only
  RR 1.12 [0.82, 1.51]
  1 study · 1298 participants
  Low

Vitamin D vs placebo or no intervention

Vitamin D supplementation probably leads to lower low birthweight (less than 2500 g) compared with placebo or no intervention (moderate certainty).

• Vitamin D supplementation for women during pregnancy 2019 · Cochrane Headline outcomes only
  RR 0.55 [0.35, 0.87]
  5 studies · 697 participants
  Moderate

Any supplements containing iron vs same supplements without iron or no treatment/placebo (no iron or placebo)

(Infant outcomes) Any supplements containing iron showed no clear difference in low birthweight (less than 2500 g) (ALL) compared with same supplements without iron or no treatment/placebo (no iron or… (low certainty).

• Daily oral iron supplementation during pregnancy 2015 · Cochrane Headline outcomes only
  RR 0.84 [0.69, 1.03]
  11 studies · 17613 participants
  Low

Any supplements containing iron and folic acid vs same supplements without iron nor folic acid (no iron nor folic acid or placebo)

(Infant outcomes) Any supplements containing iron and folic acid showed no clear difference in low birthweight (less than 2500 g) (ALL) compared with same supplements without iron nor folic acid (no iron nor folic acid… (low certainty).

• Daily oral iron supplementation during pregnancy 2015 · Cochrane Headline outcomes only
  RR 1.07 [0.31, 3.74]
  2 studies · 1311 participants
  Low

Any intermittent iron regimen (with or without other vitamins and minerals) vs daily regimen (with same vitamins and minerals)‐maternal outcomes

Any intermittent iron regimen (with or without other vitamins and… showed no clear difference in low birthweight (less than 2500 g) compared with daily regimen (with same vitamins and minerals)‐infant outcomes (low certainty).

• Intermittent oral iron supplementation during pregnancy 2015 · Cochrane Headline outcomes only
  RR 0.82 [0.55, 1.22]
  8 studies · 1898 participants
  Low

Home (point‐of‐use) fortification of foods with multiple micronutrient powders vs multiple micronutrients (MMN)

• Multiple micronutrient powders for home (point‐of‐use) fortification of foods in pregnant women 2015 · Cochrane Headline outcomes only
  no estimate extracted
  0 participants
  GRADE not reported

Home (point‐of‐use) fortification of foods with multiple micronutrient powders vs iron folic acid (IFA)

• Multiple micronutrient powders for home (point‐of‐use) fortification of foods in pregnant women 2015 · Cochrane Headline outcomes only
  no estimate extracted
  0 participants
  GRADE not reported

Intervention not reported

The intervention showed no clear difference in low birthweight (less than 2500 g) ‐ assuming independence between… (low certainty).

• Bed rest with and without hospitalisation in multiple pregnancy for improving perinatal outcomes 2017 · Cochrane Headline outcomes only
  RR 0.95 [0.75, 1.21]
  3 studies · 502 participants
  Low

Intervention not reported

The review found no eligible studies for this question.

• Bed rest with and without hospitalisation in multiple pregnancy for improving perinatal outcomes 2017 · Cochrane Headline outcomes only
  no estimate extracted
  Studies not reported
  No studies found