What do systematic reviews say?

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

Any antihypertensive drug vs no antihypertensive drugs/placebo

Any antihypertensive drug showed no clear difference in preterm birth (< 37 weeks) compared with no antihypertensive drugs/placebo (moderate certainty).

• Antihypertensive drug therapy for mild to moderate hypertension during pregnancy 2018 · Cochrane Headline outcomes only
  RR 0.96 [0.83, 1.12]
  15 studies · 2141 participants
  Moderate

Intervention not reported

The intervention leads to lower preterm birth < 37 weeks (high certainty).

• Omega‐3 fatty acid addition during pregnancy 2018 · Cochrane Headline outcomes only
  RR 0.89 [0.81, 0.97]
  26 studies · 10304 participants
  High

Intervention not reported

The intervention leads to lower early preterm birth < 34 weeks (high certainty).

• Omega‐3 fatty acid addition during pregnancy 2018 · Cochrane Headline outcomes only
  RR 0.58 [0.44, 0.77]
  9 studies · 5204 participants
  High

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

Outcomes for all interventions for smoking cessation in pregnancy vs control: subgrouped by main intervention strategy (comparison 20)

Outcomes for all interventions for smoking cessation in pregnancy showed no clear difference in preterm birth (under 37 weeks) compared with control: subgrouped by main intervention strategy (comparison 20) (high certainty).

• Psychosocial interventions for supporting women to stop smoking in pregnancy 2017 · Cochrane Headline outcomes only
  RR 0.93 [0.77, 1.11]
  19 studies · 9222 participants
  High

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

Intervention not reported

The intervention showed no clear difference in very preterm birth (less than 34 weeks) ‐ assuming complete… (low certainty).

• Bed rest with and without hospitalisation in multiple pregnancy for improving perinatal outcomes 2017 · Cochrane Headline outcomes only
  RR 1.02 [0.66, 1.58]
  5 studies · 495 participants
  Low

Intervention not reported

The intervention showed no clear difference in very preterm birth (less than 34 weeks) ‐ assuming complete… (low certainty).

• Bed rest with and without hospitalisation in multiple pregnancy for improving perinatal outcomes 2017 · Cochrane Headline outcomes only
  RR 2.3 [0.84, 6.27]
  1 study · 141 participants
  Low

Acupuncture vs placebo

Acupuncture showed no clear difference in preterm birth less than 37 weeks compared with placebo (low certainty).

• Interventions for treating hyperemesis gravidarum 2016 · Cochrane Headline outcomes only
  RR 0.12 [0.01, 2.26]
  1 study · 36 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

External cephalic version (ECV) commenced before term vs ECV at term

External cephalic version (ECV) commenced before term leads to higher preterm birth < 37 weeks compared with ECV at term (high certainty).

• External cephalic version for breech presentation before term 2015 · Cochrane Headline outcomes only
  RR 1.51 [1.03, 2.21]
  3 studies · 1888 participants
  High

Pyridoxine vs control

• Pyridoxine (vitamin B6) supplementation during pregnancy or labour for maternal and neonatal outcomes 2015 · Cochrane Headline outcomes only
  no estimate extracted
  0 participants
  GRADE not reported

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

All routine Doppler ultrasound vs no Doppler ultrasound

All routine Doppler ultrasound showed no clear difference in preterm birth (before 37 weeks) compared with no Doppler ultrasound (high certainty).

• Fetal and umbilical Doppler ultrasound in normal pregnancy 2015 · Cochrane Headline outcomes only
  RR 1.02 [0.86, 1.21]
  4 studies · 12162 participants
  High