Multiple micronutrients showed no clear difference in preterm births compared with control (iron with or without folic acid) (moderate certainty).
Main comparison (FFN knowledge showed no clear difference in preterm birth < 37 weeks compared with no knowledge) (low certainty).
Main comparison (FFN knowledge showed no clear difference in preterm birth < 34 weeks compared with no knowledge) (low certainty).
It is very uncertain whether main comparison (FFN knowledge changes preterm birth < 32 weeks compared with no knowledge) (very low certainty).
It is very uncertain whether the intervention changes preterm birth < 37 weeks (very low certainty).
Vitamin D + calcium supplementation may leads to higher preterm birth (less than 37 weeks' gestation) compared with placebo or no intervention (low certainty).
Vitamin D + calcium + other vitamins and minerals showed no clear difference in preterm birth (less than 37 weeks' gestation) compared with calcium + other vitamins and minerals (but no vitamin D) (low certainty).
Vitamin D supplementation showed no clear difference in preterm birth (less than 37 weeks' gestation) compared with placebo or no intervention (low certainty).
Calcium supplementation showed no clear difference in pregnancy loss or stillbirth at any gestational age compared with placebo (maternal outcomes) commencing before or early (low certainty).
Calcium showed no clear difference in pregnancy loss, stillbirth or NND before discharge compared with placebo (offspring outcomes) commencing before or early (low certainty).
Vaginal progesterone showed no clear difference in preterm birth less than 37 weeks compared with no treatment or placebo (moderate certainty).
Vaginal progesterone showed no clear difference in preterm birth less than 28 weeks compared with no treatment or placebo (low certainty).
Intramuscular (IM) progesterone may leads to higher preterm birth less than 34 weeks compared with no treatment or placebo (low certainty).
Intramuscular (IM) progesterone showed no clear difference in preterm birth less than 28 weeks compared with no treatment or placebo (moderate certainty).
Intramuscular (IM) progesterone showed no clear difference in preterm birth less than 37 weeks compared with no treatment or placebo (high certainty).
Vaginal progesterone showed no clear difference in preterm birth less than 34 weeks compared with no treatment or placebo (low certainty).
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).
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).
The intervention may leads to lower preterm birth (low certainty).
Any antihypertensive drug showed no clear difference in preterm birth (< 37 weeks) compared with no antihypertensive drugs/placebo (moderate certainty).