Table 3.

Nutrients with known efficacy to reduce the risk of PTB.

Nutrient	Evidence for Efficacy	Dose	Duration	Comments
n−3 LC-PUFA (combinations of EPA and DHA)	26–61% reduction in the risk of early PTB	DHA: 133 to 2100 mg DHA/day EPA: 100 to 3000 mg EPA/day	Supplementation started between 12 to 30 weeks of gestation	Eight trials supplementing either DHA or EPA alone or using varying combinations of both (five trials in healthy pregnancies and three in at-risk pregnancies), two food-based interventions and 6 meta-analyses
DHA (predominantly DHA)	51.6% to 87.5% reduction in the risk of early PTB (<34 weeks)	600 to 800 mg DHA/day	Supplementation started <20 to 21 weeks of gestation	Two large RCTs available where PTB and EPTB were secondary outcomes and not the primary outcome.
Zinc	14% reduction in PTB	5 mg/day to 44 mg/day	Supplementations started from as early as before conception (one study) to at least starting before 26 weeks	Most studies were conducted in low income countries among women with poor nutritional status and likely to have low zinc concentrations. The reduction in PTB was not accompanied by reduction in LBW or a difference in the gestational age at birth.
Vitamin D	64% reduction in PTB	400 to 1000 IU/day (two trials), 60000–12000 IU (depending on baseline serum 25 (OH)D (one trial) cholecalciferol D3	Supplementation started between 20–30 weeks of gestation	The trials available were all of low quality.

DHA: docosahexaenoic acid, EPA: eicosapentanoic acid, EPTB: early PTB, PTB: preterm Birth, LBW: low birth weight.