Preterm labor
Supplements studied for preterm labor.
Overview
Algal Oil (3 studies) is the most promising supplement for preterm labor prevention, with trials suggesting that about 1000 mg daily of DHA from algae—especially in women with low pre-pregnancy DHA—may lower early preterm birth risk. A meta-analysis of myo-Inositol with folic acid (1 study source) reported roughly two-thirds lower preterm delivery risk in gestational-diabetes–prone women, though generalizability is uncertain.
Iron (3 studies) does not generally prolong pregnancy, and Vitamin C (3 studies) and Vitamin B6 (2 studies) show no meaningful benefit for preventing preterm labor. See the heatmap and evidence reviews below for full evidence.
Effect graph
Relevant supplements
Relevant supplements sorted by DEX Score.
| Inositol | ★★★★★ | Medium |
| Algal Oil | ★★★★★ | Medium |
| Vitamin D | ★★★★★ | Low |
| Vitamin B6 | ★★★★★ | Low |
| Nattokinase | ★★★★★ | Low |
| N-Acetyl Cysteine (NAC) | ★★★★★ | Low |
| Alpha-Lipoic Acid | ★★★★★ | Low |
| Vitamin C | ★★★★★ | Very Low / None |
| Vitamin B9 (Folate) | ★★★★★ | Very Low / None |
| Iron | ★★★★★ | Very Low / None |
Studies
Find individual evidence reviews for supplements sorted by DEX Score.
10 supplements for and rated at least stars. All purchase bands. No minimum star filter.
Algal OilView supplement →
Consider purchase·★★★★★
How we scored this▸
- Taking DHA algae oil supplements during pregnancy may help prevent early preterm labor in women who have low DHA levels before pregnancy.
- Studies show that taking about 1000 mg of DHA daily from algae, starting in early pregnancy, lowers the chance of giving birth too early compared to lower doses.
- The benefits are strongest for those with low DHA levels at the start and less clear for those with higher DHA levels.
Browse 3 studies
RCTDocosahexaenoic acid (DHA) intake estimated from a 7-question survey identifies pregnancies most likely to benefit from high-dose DHA supplementation2023n=810
A secondary analysis found women with low dietary DHA intake had fewer early preterm births when assigned to high-dose DHA supplementation in two prior RCTs.
- Effect
- Benefit
- Duration
- remainder of pregnancy
- Dose
- 200 mg/day
- Population
- Women
- Participants
- 810
RCTEarly and late preterm birth rates in participants adherent to randomly assigned high dose docosahexaenoic acid (DHA) supplementation in pregnancy2023
Per-protocol analysis of an RCT in pregnant women adherent to 1000 mg/day DHA found lower early preterm birth rates than in the intention-to-treat population, though intention-to-treat results were null.
- Effect
- Benefit
- Dose
- 1000 mg/day
- Population
- Women
RCTHigher dose docosahexaenoic acid supplementation during pregnancy and early preterm birth: A randomised, double-blind, adaptive-design superiority trial2021n=1,100
A clinical trial including 1,100 participants found that taking 1000 mg DHA (from 2g algal oil) during pregnancy (starting at 12-20 weeks' gestation until delivery) was superior to 200 mg DHA daily. The higher dose led to a reduced rate of early preterm birth (EPB, < 34 weeks) of 1.7% compared to 2.4% in those taking 200 mg DHA daily. The higher dose was associated with fewer serious adverse effects, but supplementation was only effective in women with low DHA status.
- Effect
- Benefit
- Duration
- 12–20 weeks
- Dose
- 1000 mg/day
- Population
- Women
- Participants
- 1,100
InositolView supplement →
Consider purchase·★★★★★
How we scored this▸
- Research combining several clinical studies suggests that taking myo-inositol and folic acid every day during pregnancy can lower the risk of early (preterm) delivery by about two-thirds for women at higher risk for gestational diabetes.
- Most women in these studies took myo-inositol twice a day beginning in the first trimester.
- It’s uncertain if the same benefits would apply to women at low risk of gestational diabetes.
Browse 1 study·1 meta-analysis
MetaThe efficacy of myo-inositol supplementation to prevent gestational diabetes onset: a meta-analysis of randomized controlled trials2019
A meta-analysis of RCTs found myo-inositol supplementation significantly reduced gestational diabetes onset in pregnant women versus control.
- Effect
- Benefit
- Population
- Women
Vitamin DView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Low vitamin D levels in pregnancy may increase the chance of having a premature baby, especially in people with darker skin.
- However, taking vitamin D supplements during pregnancy has not consistently been shown to lower this risk.
- Some studies suggest that vitamin d supplementation might help if vitamin D levels are very low, but more research is needed.
- Doctors recommend taking vitamin D during pregnancy to help lower the risk of early birth and other problems, even though the evidence is not very strong.
Browse 6 studies·3 meta-analyses
MetaVitamin D supplementation for women during pregnancy2024n=1,368
An updated Cochrane review of 10 RCTs (2,313 pregnant women) found vitamin D alone may reduce severe postpartum hemorrhage and low birthweight, but evidence was low to very low certainty.
- Effect
- Benefit
- Population
- Women
- Participants
- 1,368
MetaEffects of vitamin D supplementation during pregnancy on offspring health at birth: A meta-analysis of randomized controlled trails2022n=11,082
A meta-analysis of 42 pregnancy RCTs (11,082 participants) found vitamin D supplementation reduced intrauterine or neonatal death (RR 0.69) and increased birth length but not birth weight.
- Effect
- Benefit
- Dose
- 400 IU/day
- Population
- Pregnant women
- Participants
- 11,082
ObservationalFirst Trimester Maternal Vitamin D Status and Risks of Preterm Birth and Small-For-Gestational Age2019
A prospective cohort of 2,813 pregnant women found first-trimester 25(OH)D <20 ng/mL associated with higher preterm birth risk; results varied by skin type.
- Effect
- Benefit
- Population
- Women
- Ages
- 18+
MetaVitamin D and risk of preterm birth: Up-to-date meta-analysis of randomized controlled trials and observational studies2017
A meta-analysis found low maternal vitamin D associated with preterm birth in observational studies, but vitamin D supplementation RCTs showed no significant risk reduction.
- Effect
- No Benefit
- Population
- Pregnant women
MetaVitamin D supplementation during pregnancy: state of the evidence from a systematic review of randomised trials2017n=8,406
A systematic review of 43 prenatal vitamin D RCTs (8,406 participants) found supplementation increased birth weight and reduced wheeze by age 3 but showed limited maternal clinical benefit.
- Effect
- Benefit
- Dose
- 600 IU/day
- Population
- Pregnant women
- Participants
- 8,406
MetaVitamin D during pregnancy and maternal, neonatal and infant health outcomes: a systematic review and meta-analysis2012
A review of 5 small pregnancy vitamin D RCTs found supplementation may reduce low birthweight (RR 0.40) but evidence for other perinatal outcomes was limited.
- Effect
- Benefit
- Population
- Pregnant women
Vitamin B6View supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Taking vitamin B6 by mouth or injection does not seem to lower the chance of early labor (preterm labor).
- Studies using daily doses of 25 mg or a single 100 mg dose found no benefit compared to no treatment.
- The research available is limited.
Browse 2 studies·2 meta-analyses
MetaPyridoxine (vitamin B6) supplementation during pregnancy or labour for maternal and neonatal outcomes2015n=1,242
A meta-analysis of 1242 participants found that vitamin B6 as oral capsules or lozenges resulted in decreased risk of dental decay in pregnant women (capsules: risk ratio (RR) 0.84; 95% confidence interval (CI) 0.71 to 0.98; one trial, n = 371, low quality of evidence; lozenges: RR 0.68; 95% CI 0.56 to 0.83; one trial, n =.
- Effect
- No Benefit
- Population
- Women
- Participants
- 1,242
MetaInterventions with vitamins B6, B12 and C in pregnancy2012
A meta-analysis found that in meta-analyses, vitamins C and E increased the risk of pregnancy-related hypertension (relative risk 1.10 [95% CI 1.02, 1.19]).
- Effect
- Benefit
- Dose
- 217 g/day
- Population
- Pregnant women
Alpha-Lipoic AcidView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- It is not yet clear if alpha-lipoic acid can help prevent preterm birth.
- Early research suggests that applying 400 mg of alpha-lipoic acid vaginally once a night for 30 days after preterm labor may help prevent the cervix from shortening, but it is unknown if this lowers the chance of giving birth early.
Browse 1 study
RCTVaginal alpha-lipoic acid shows an anti-inflammatory effect on the cervix, preventing its shortening after primary tocolysis. A pilot, randomized, placebo-controlled study2017n=20
In 37 women at 24–30 weeks after preterm labor, vaginal alpha-lipoic acid 400 mg daily for 30 days raised anti-inflammatory cytokines and stabilized cervical length while placebo group cervical length shortened.
- Effect
- Benefit
- Duration
- 30 days
- Dose
- 400 mg/day
- Population
- Women
- Participants
- 20
N-Acetyl Cysteine (NAC)View supplement →
Reconsider purchase·★★★★★
How we scored this▸
- It is unclear if N-acetylcysteine (NAC) helps reduce the likelihood of preterm labor.
- Some studies show taking NAC with 17-hydroxyprogesterone starting early in pregnancy helps women with past early labor and vaginal infections carry closer to full term.
- But taking NAC later in pregnancy for women with severe pre-eclampsia or HELLP syndrome doesn’t seem to delay delivery.
Browse 2 studies
RCTEffect of oral N-acetyl cysteine on recurrent preterm labor following treatment for bacterial vaginosis2009n=280
A double-blind RCT in 280 women (16–18 weeks pregnant) with prior preterm birth and treated bacterial vaginosis found 0.6 g/day NAC plus 17-OHPC raised gestational age at delivery versus placebo (37.4 vs 34.1 weeks).
- Effect
- Benefit
- Duration
- 1 week
- Dose
- 0.6 g/day
- Population
- Women
- Participants
- 280
RCTOral N-acetylcysteine administration does not stabilise the process of established severe preeclampsia2006
In a double-blind RCT, oral NAC did not prolong treatment-to-delivery interval or improve maternal or neonatal outcomes in women with early-onset severe preeclampsia and/or HELLP syndrome.
- Effect
- No Benefit
- Population
- Women
NattokinaseView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- There is not enough evidence to determine if nattokinase has any benefit for preterm labor.
Browse 1 study
RCTThe Effect of Soy Intake on Metabolic Profiles of Women With Gestational Diabetes Mellitus2015n=34
In 68 women with gestational diabetes, a soy diet (35% soy protein) for 6 weeks lowered fasting glucose, insulin, and HOMA-IR and raised insulin sensitivity vs a 70% animal-protein control diet.
- Effect
- Benefit
- Duration
- 6 weeks
- Dose
- 0.8 g/kg/day protein (35% soy)
- Population
- Women
- Participants
- 34
IronView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Taking iron tablets during pregnancy does not seem to make babies bigger at birth or make pregnancies last longer in most cases.
- But in women who are pregnant for the first time and live in areas where malaria is common, taking iron and folic acid before and early in pregnancy may increase the chance of giving birth early.
- This may happen because malaria causes changes in iron in the body that lead to inflammation.
Browse 3 studies·1 meta-analysis
RCTExcess risk of preterm birth with periconceptional iron supplementation in a malaria endemic area: analysis of secondary data on birth outcomes in a double blind randomized controlled safety trial in Burkina Faso2019n=1,959
In 478 nulliparous Burkinabé women, weekly periconceptional iron plus folic acid was associated with lower birthweight (−111 g) and higher preterm birth risk (27.5% vs 13.9%) in a malaria-endemic setting.
- Effect
- No Benefit
- Duration
- 18 months
- Dose
- 60 mg
- Population
- Women
- Participants
- 1,959
- Ages
- 15–24
RCTTesting an infection model to explain excess risk of preterm birth with long-term iron supplementation in a malaria endemic area2019
Analysis of the Burkina Faso iron trial proposed dual inflammatory pathways linking long-term iron supplementation, raised hepcidin, and increased preterm birth risk in malaria-endemic first pregnancies.
- Population
- Women
MetaEffect of iron intervention on growth during gestation, infancy, childhood, and adolescence: a systematic review with meta-analysis2013
A meta-analysis through February 2010 found iron interventions had little overall effect on height, weight, head circumference, or birth weight across gestation, infancy, childhood, and adolescence.
- Dose
- 40–66 mg/day
- Population
- Women
- Ages
- 6+
Vitamin B9 (Folate)View supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Reviews of research show that taking folic acid during pregnancy does not lower the chance of having a premature birth.
- One study found that pregnant women with epilepsy who took folic acid while on antiseizure medicine had a lower risk of premature birth.
- However, folic acid did not affect premature birth risks in women without epilepsy or those with epilepsy not using these medicines.
Browse 3 studies·2 meta-analyses
ObservationalFolic Acid and Risk of Preterm Birth, Preeclampsia, and Fetal Growth Restriction Among Women With Epilepsy: A Prospective Cohort Study2022n=64
An observational study of 64 women found that aSM-treated women with epilepsy starting folic acid after the first trimester had a higher risk compared with women without epilepsy with similar timing of folic acid (aOR 2.6, 95% CI 1.1-6.5), and even higher if not using folic acid (aOR 9.4, 95% CI 2.6-34.8).
- Effect
- No Benefit
- Duration
- 4 weeks before pregnancy to 12 weeks gestation
- Population
- Women
- Participants
- 64
MetaFolic acid supplementation in pregnancy to prevent preterm birth: a systematic review and meta-analysis of randomized controlled trials2016n=5,332
A meta-analysis of 5 RCTs in 5,332 women found folic acid supplementation did not reduce preterm birth before 37 weeks versus control (22.6% vs 22.9%).
- Effect
- No Benefit
- Population
- Women
- Participants
- 5,332
MetaFolic acid supplementation during pregnancy for maternal health and pregnancy outcomes2013n=17,771
A meta-analysis of 17771 participants found that this review found that folic acid supplementation has no impact on pregnancy outcomes such as preterm birth (risk ratio (RR) 1.01, 95% confidence interval (CI) 0.73 to 1.38; three studies, 2959 participants), and stillbirths/neonatal deaths (RR 1.33, 95% CI 0.96 to 1.85;.
- Effect
- No Benefit
- Population
- Women
- Participants
- 17,771
Vitamin CView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Vitamin C has no meaningful benefit for Preterm labor.
Browse 3 studies·2 meta-analyses
MetaVitamin C supplementation in pregnancy2015n=24,300
A Cochrane review of 29 trials (24,300 pregnant women) found vitamin C did not prevent preterm birth, preeclampsia, or stillbirth overall.
- Effect
- No Benefit
- Population
- Women
- Participants
- 24,300
MetaSupplementation with vitamins C and E during pregnancy for the prevention of preeclampsia and other adverse maternal and perinatal outcomes: a systematic review and metaanalysis2011n=19,810
A meta-analysis of 9 trials (19,810 women) found vitamins C and E during pregnancy did not prevent preeclampsia and increased gestational hypertension.
- Effect
- No Benefit
- Population
- Women
- Participants
- 19,810
MetaA meta-analysis on the efficacy and safety of combined vitamin C and E supplementation in preeclamptic women2009
A meta-analysis of 7 trials (5,969 women) found combined vitamins C and E increased gestational hypertension and low birth weight without reducing preeclampsia.
- Effect
- No Benefit
- Population
- Women
Evidence visualised
Same ratings as above, aggregated so you can see coverage and imbalance.
| Supplement | DEX | Studies | Meta-analyses | Share |
|---|---|---|---|---|
| Vitamin D | ★★★★★52% | 6 | 3 | 24% |
| Algal Oil | ★★★★★64% | 3 | 0 | 12% |
| Iron | ★★★★★40% | 3 | 1 | 12% |
| Vitamin B9 (Folate) | ★★★★★40% | 3 | 2 | 12% |
| Vitamin C | ★★★★★40% | 3 | 2 | 12% |
| N-Acetyl Cysteine (NAC) | ★★★★★44% | 2 | 0 | 8% |
| Vitamin B6 | ★★★★★48% | 2 | 2 | 8% |
| Alpha-Lipoic Acid | ★★★★★44% | 1 | 0 | 4% |
| Inositol | ★★★★★64% | 1 | 1 | 4% |
| Nattokinase | ★★★★★44% | 1 | 0 | 4% |