What do systematic reviews say?

Probiotics administered to pregnant women at risk of preterm birth vs placebo or no intervention

Probiotics administered to pregnant women at risk of preterm birth showed no clear difference in preterm birth < 37 weeks' gestation compared with placebo or no intervention (low certainty).

• Maternal probiotic supplementation for prevention of morbidity and mortality in preterm infants 2018 · Cochrane Headline outcomes only
  RR 0.92 [0.32, 2.67]
  4 studies · 518 participants
  Low

Probiotics administered to pregnant women at risk of preterm birth vs placebo or no intervention

• Maternal probiotic supplementation for prevention of morbidity and mortality in preterm infants 2018 · Cochrane Headline outcomes only
  no estimate extracted
  2 studies · 287 participants
  Very low

Preterm birth (<37 weeks gestation) vs Full-term birth (37 weeks or more gestation)

Mean DMFT was 1.00 in preterm children versus 0.38 in full-term children.

• Oral Health of Children and Adolescents in the United Arab Emirates: A Systematic Review of the Past Decade. 2021 All outcomes

  Preterm children
  MEAN 1.00
  1 study
  GRADE not reported

Women who experienced preterm birth vs Women who did not experience preterm birth (term)

Women who experienced preterm birth did not have a significantly different DMFS than those who did not (mean difference -0.15, 95% CI -3.40 to 3.09; 3 studies; I2=89%); certainty of evidence not graded.

• Dental caries and preterm birth: a systematic review and meta-analysis. 2018 All outcomes

  Pregnant women assessed around delivery in observational studies across multiple countries (Mexico, Malawi, India, France, Jordan, Finland, Tanzania); mostly retrospective cohort and case-control designs
  MD -0.15 [-3.40, 3.09]
  3 studies · 2594 participants
  GRADE not reported

Women who experienced preterm birth vs Women who did not experience preterm birth (term)

Women who experienced preterm birth did not have significantly higher DMFT than those who did not (mean difference 1.56, 95% CI -0.28 to 3.41; 5 studies; I2=92%); certainty of evidence not graded.

• Dental caries and preterm birth: a systematic review and meta-analysis. 2018 All outcomes

  Pregnant women assessed around delivery in observational studies across multiple countries (Mexico, Malawi, India, France, Jordan, Finland, Tanzania); mostly retrospective cohort and case-control designs
  MD 1.56 [-0.28, 3.41]
  5 studies · 2963 participants
  GRADE not reported

Probiotics administered to pregnant women at risk of preterm birth vs placebo or no intervention

• Maternal probiotic supplementation for prevention of morbidity and mortality in preterm infants 2018 · Cochrane Headline outcomes only
  no estimate extracted
  2 studies · 207 participants
  Low

Probiotics administered to pregnant women at risk of preterm birth vs placebo or no intervention

Probiotics administered to pregnant women at risk of preterm birth showed no clear difference in miscarriage/stillbirth compared with placebo or no intervention (low certainty).

• Maternal probiotic supplementation for prevention of morbidity and mortality in preterm infants 2018 · Cochrane Headline outcomes only
  RR 0.79 [0.2, 3.14]
  2 studies · 320 participants
  Low

Preterm birth (PTB) group vs Term birth (TB) group

Shannon diversity did not differ significantly between preterm and term birth (certainty not rated).

• The role of oral dysbiosis in pregnancy complications: a systematic review and meta-analysis of preterm birth. 2026 All outcomes

  Oral samples (saliva or subgingival plaque), 16S rRNA sequencing
  MD 1.09 [-0.55, 2.73]
  4 studies · 296 participants
  GRADE not reported

Preterm birth (PTB) group vs Term birth (TB) group

In saliva samples Shannon diversity did not differ between preterm and term birth.

• The role of oral dysbiosis in pregnancy complications: a systematic review and meta-analysis of preterm birth. 2026 All outcomes

  Oral samples (saliva or subgingival plaque), 16S rRNA sequencing · Sample site: saliva
  MD 0.16 [-0.22, 0.53]
  2 studies · 114 participants
  GRADE not reported

Preterm birth (PTB) group vs Term birth (TB) group

In V3-V4 studies Shannon diversity did not differ significantly, with very high heterogeneity.

• The role of oral dysbiosis in pregnancy complications: a systematic review and meta-analysis of preterm birth. 2026 All outcomes

  Oral samples (saliva or subgingival plaque), 16S rRNA sequencing · Amplified 16S rRNA region: V3-V4
  MD 1.37 [-0.83, 3.57]
  3 studies · 242 participants
  GRADE not reported

Preterm birth (PTB) group vs Term birth (TB) group

In subgingival plaque Shannon diversity did not differ significantly, with very high heterogeneity.

• The role of oral dysbiosis in pregnancy complications: a systematic review and meta-analysis of preterm birth. 2026 All outcomes

  Oral samples (saliva or subgingival plaque), 16S rRNA sequencing · Sample site: subgingival plaque
  MD 2.02 [-1.1, 5.15]
  2 studies · 182 participants
  GRADE not reported

Preterm birth (PTB) group vs Term birth (TB) group

Sensitivity analysis with Wan conversion gave a similar non-significant difference.

• The role of oral dysbiosis in pregnancy complications: a systematic review and meta-analysis of preterm birth. 2026 All outcomes

  Oral samples (saliva or subgingival plaque), 16S rRNA sequencing · Sensitivity analysis: Wan et al. conversion of summary statistics
  MD 1.07 [-0.48, 2.62]
  4 studies · 296 participants
  GRADE not reported

Preterm birth (PTB) group vs Term birth (TB) group

In Asian studies Shannon diversity did not differ significantly between preterm and term birth.

• The role of oral dysbiosis in pregnancy complications: a systematic review and meta-analysis of preterm birth. 2026 All outcomes

  Oral samples (saliva or subgingival plaque), 16S rRNA sequencing · Geographic region: Asia
  MD 0.28 [-0.00, 0.56]
  3 studies · 200 participants
  GRADE not reported

Preterm birth (PTB) group vs Term birth (TB) group

Sensitivity analysis with Hozo conversion gave a similar non-significant difference.

• The role of oral dysbiosis in pregnancy complications: a systematic review and meta-analysis of preterm birth. 2026 All outcomes

  Oral samples (saliva or subgingival plaque), 16S rRNA sequencing · Sensitivity analysis: Hozo et al. conversion of summary statistics
  MD 0.98 [-0.43, 2.38]
  4 studies · 296 participants
  GRADE not reported

Cerclage vs no cerclage

Cerclage leads to lower preterm birth before 34 completed weeks compared with no cerclage (high certainty).

• Cervical stitch (cerclage) for preventing preterm birth in singleton pregnancy 2017 · Cochrane Headline outcomes only
  RR 0.77 [0.66, 0.89]
  9 studies · 2415 participants
  High

Preterm birth (<37 weeks gestation) vs Full-term birth (37 weeks or more gestation)

In children aged 3 years or younger, preterm birth was not associated with early childhood caries (OR 0.90, 95% CI 0.59 to 1.37); certainty not graded.

• Relationship between preterm, low birth weight and early childhood caries: a meta-analysis of the case-control and… 2020 All outcomes

  Community/epidemiological studies of preschool children (multiple countries) · Children aged 3 years or younger
  OR 0.90 [0.59, 1.37]
  2 studies
  GRADE not reported
• Relationship between preterm, low birth weight and early childhood caries: a meta-analysis of the case-control and… 2020 All outcomes

  Community/epidemiological studies of preschool children (multiple countries) · Overall
  OR 1.59 [1.36, 1.87]
  16 studies · 21279 participants
  GRADE not reported

Intervention not reported

The intervention leads to lower preterm birth less than 34 weeks' gestation (high certainty).

• Home uterine monitoring for detecting preterm labour 2017 · Cochrane Headline outcomes only
  RR 0.78 [0.62, 0.99]
  3 studies · 1596 participants
  High

Intervention not reported

It is very uncertain whether the intervention changes preterm birth less than 37 weeks' gestation (very low certainty).

• Home uterine monitoring for detecting preterm labour 2017 · Cochrane Headline outcomes only
  RR 0.85 [0.72, 1.01]
  8 studies · 4834 participants
  Very low

Main comparison (FFN knowledge vs no knowledge)

Main comparison (FFN knowledge showed no clear difference in preterm birth < 37 weeks compared with no knowledge) (low certainty).

• Fetal fibronectin testing for reducing the risk of preterm birth 2019 · Cochrane Headline outcomes only
  RR 0.72 [0.52, 1.01]
  5 studies · 434 participants
  Low

Main comparison (FFN knowledge vs no knowledge)

Main comparison (FFN knowledge showed no clear difference in preterm birth < 34 weeks compared with no knowledge) (low certainty).

• Fetal fibronectin testing for reducing the risk of preterm birth 2019 · Cochrane Headline outcomes only
  RR 1.09 [0.54, 2.18]
  4 studies · 357 participants
  Low