What do systematic reviews say?

A dose of vitamin D 601 IU or higher vs 600 IU or lower alone or with other nutrients

A dose of vitamin D 601 IU or higher showed no clear difference in preterm birth compared with 600 IU or lower alone or with other nutrients (low certainty).

• Regimens of vitamin D supplementation for women during pregnancy 2019 · Cochrane Headline outcomes only
  RR 1.25 [0.92, 1.69]
  4 studies · 2294 participants
  Low

A dose of vitamin D 4000 IU/d or more vs 3999 IU/d or less alone or with any other nutrient

A dose of vitamin D 4000 IU/d or more showed no clear difference in preterm birth compared with 3999 IU/d or less alone or with any other nutrient (low certainty).

• Regimens of vitamin D supplementation for women during pregnancy 2019 · Cochrane Headline outcomes only
  RR 0.85 [0.64, 1.12]
  6 studies · 2948 participants
  Low

Intervention not reported

The intervention may leads to lower preterm birth (low certainty).

• Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems 2018 · Cochrane Headline outcomes only
  RR 0.76 [0.6, 0.97]
  11 studies · 15275 participants
  Low

Progesterone vs placebo or no treatment

Progesterone showed no clear difference in preterm birth compared with placebo or no treatment (low certainty).

• Progestogen for treating threatened miscarriage 2018 · Cochrane Headline outcomes only
  RR 0.86 [0.52, 1.44]
  5 studies · 588 participants
  Low

Any supplement containing iodine vs same supplement without iodine or no treatment/placebo (maternal outcomes)

Any supplement containing iodine showed no clear difference in preterm birth compared with same supplement without iodine or no treatment/placebo (maternal… (low certainty).

• Iodine supplementation for women during the preconception, pregnancy and postpartum period 2017 · Cochrane Headline outcomes only
  RR 0.71 [0.3, 1.66]
  2 studies · 376 participants
  Low

Corticosteroids vs promethazine

Corticosteroids showed no clear difference in preterm birth compared with promethazine (low certainty).

• Interventions for treating hyperemesis gravidarum 2016 · Cochrane Headline outcomes only
  RR 3 [0.13, 69.52]
  1 study · 40 participants
  Low

Corticosteroids vs placebo

It is very uncertain whether corticosteroids changes preterm birth compared with placebo (very low certainty).

• Interventions for treating hyperemesis gravidarum 2016 · Cochrane Headline outcomes only
  RR 1.01 [0.31, 3.28]
  2 studies · 134 participants
  Very low

Balanced protein and energy supplementation vs no intervention or control intervention (control)

Balanced protein and energy supplementation showed no clear difference in preterm birth compared with control or no intervention (moderate certainty).

• Antenatal dietary education and supplementation to increase energy and protein intake 2015 · Cochrane Headline outcomes only
  RR 0.96 [0.8, 1.16]
  5 studies · 3384 participants
  Moderate

Intervention not reported

The intervention showed no clear difference in preterm birth (low certainty).

• Antenatal dietary education and supplementation to increase energy and protein intake 2015 · Cochrane Headline outcomes only
  RR 1.14 [0.83, 1.56]
  1 study · 505 participants
  Low

Intervention not reported

• Antenatal dietary education and supplementation to increase energy and protein intake 2015 · Cochrane Headline outcomes only
  no estimate extracted
  0 studies · 0 participants
  GRADE not reported

Nutritional education vs no counselling or education during pregnancy

Nutritional education may leads to lower preterm birth compared with no counselling or education during pregnancy (low certainty).

• Antenatal dietary education and supplementation to increase energy and protein intake 2015 · Cochrane Headline outcomes only
  RR 0.46 [0.21, 0.98]
  2 studies · 449 participants
  Low

Reduced number of antenatal care visits/goal‐oriented vs standard antenatal care visits

Reduced number of antenatal care visits/goal‐oriented showed no clear difference in preterm birth compared with standard antenatal care visits (moderate certainty).

• Alternative versus standard packages of antenatal care for low‐risk pregnancy 2015 · Cochrane Headline outcomes only
  RR 1.02 [0.94, 1.11]
  7 studies · 53661 participants
  Moderate

Caffeinated (experimental group) vs decaffeinated group (control group)

Caffeinated (experimental group) showed no clear difference in preterm birth compared with decaffeinated group (control group) (low certainty).

• Effects of restricted caffeine intake by mother on fetal, neonatal and pregnancy outcomes 2015 · Cochrane Headline outcomes only
  RR 0.81 [0.48, 1.37]
  1 study · 1153 participants
  Low

All diet and/or exercise interventions vs (Optimised) usual care

All diet and/or exercise interventions showed no clear difference in preterm birth compared with standard/other care (moderate certainty).

• Diet or exercise, or both, for preventing excessive weight gain in pregnancy 2015 · Cochrane Headline outcomes only
  RR 0.91 [0.68, 1.22]
  16 studies · 5923 participants
  Moderate

Intervention not reported

The intervention showed no clear difference in preterm birth (low certainty).

• Vitamin A supplementation during pregnancy for maternal and newborn outcomes 2015 · Cochrane Headline outcomes only
  RR 0.39 [0.08, 1.93]
  1 study · 136 participants
  Low

Vitamin A vs placebo or no treatment

Vitamin A alone showed no clear difference in preterm birth compared with placebo or no treatment (high certainty).

• Vitamin A supplementation during pregnancy for maternal and newborn outcomes 2015 · Cochrane Headline outcomes only
  RR 0.98 [0.94, 1.01]
  5 studies · 48007 participants
  High

Universal screening vs No screening

The review found no eligible studies for this question.

• Screening and subsequent management for thyroid dysfunction pre‐pregnancy and during pregnancy for improving maternal… 2015 · Cochrane Headline outcomes only
  no estimate extracted
  Studies not reported
  No studies found

Universal screening vs case finding

Universal screening showed no clear difference in preterm birth compared with case finding (high certainty).

• Screening and subsequent management for thyroid dysfunction pre‐pregnancy and during pregnancy for improving maternal… 2015 · Cochrane Headline outcomes only
  RR 0.99 [0.8, 1.24]
  1 study · 4516 participants
  High

Intervention not reported

The intervention showed no clear difference in preterm birth (low certainty).

• Drugs for preventing malaria in pregnant women in endemic areas: any drug regimen versus placebo or no treatment 2014 · Cochrane Headline outcomes only
  RR 0.85 [0.66, 1.1]
  2 studies · 1493 participants
  Low

Intervention not reported

• Drugs for preventing malaria in pregnant women in endemic areas: any drug regimen versus placebo or no treatment 2014 · Cochrane Headline outcomes only
  no estimate extracted
  0 studies · 0 participants
  GRADE not reported