What strategies can prevent preterm birth in at-risk individuals, including the use of low-dose Aspirin (Acetylsalicylic Acid), risk scoring, and screening for asymptomatic bacteriuria?

Effective Strategies for Prevention of Preterm Birth in At-Risk Individuals

Risk scoring in early pregnancy and low-dose aspirin beginning before 16 weeks gestation are the most effective evidence-based strategies for preventing preterm birth in at-risk individuals. 1

Risk Assessment and Screening

• Early pregnancy risk scoring: All guidelines recommend risk assessment at booking/early pregnancy to identify women at increased risk for preterm birth 1

  • Risk factors include: history of preeclampsia, prior preterm birth, chronic hypertension, pregestational diabetes, renal disease, autoimmune diseases, and multifetal gestation 1
  • First trimester screening using combinations of maternal history, uterine artery Doppler, blood pressure, and serum biomarkers (PAPP-A) can identify high-risk women 1

• Screening for asymptomatic bacteriuria:

  • Early detection and treatment of asymptomatic bacteriuria during pregnancy prevents complications including preterm labor 2
  • Women with asymptomatic bacteriuria detected and treated early (before 20 weeks) showed significantly lower rates of preterm labor compared to those detected later (32-34 weeks) 2
  • The relative risk of preterm labor was 3.27 (95% CI 1.38-7.72) in women with late-detected bacteriuria compared to bacteriuria-negative women 2

Low-Dose Aspirin Therapy

• Timing:

  • Low-dose aspirin should be initiated before 16 weeks of gestation, not at 20 weeks 1
  • Evidence shows aspirin is more effective in preventing preeclampsia and fetal growth restriction when started before 16 weeks 1, 3
  • Recent evidence supports starting aspirin as early as 6-13 weeks of gestation 4

• Dosage:

  • Most guidelines recommend 75-100 mg daily 1
  • Higher doses (100-150 mg) may be more effective than lower doses (60 mg) 1, 5
  • In obese high-risk women, 162 mg showed a 78% probability of benefit over 81 mg in reducing preeclampsia with severe features 5

• Benefits:

  • 14% reduction in preterm birth (RR 0.86,95% CI 0.76-0.98) 1
  • 20% reduction in intrauterine growth restriction (RR 0.80,95% CI 0.65-0.99) 1
  • Increased mean birthweight by 130g (95% CI 36.2-223.3g) 1
  • 24% reduction in preeclampsia (RR 0.76,95% CI 0.62-0.95) 1
  • Significant reduction in spontaneous preterm birth (RR 0.70,95% CI 0.57-0.86) in women with previous preterm birth 6

Additional Prevention Strategies

• Smoking cessation: All six national guidelines recommend smoking cessation as a key preventive measure 1

• Avoiding coitus after 18 weeks: There is no evidence in the guidelines supporting sexual abstinence after 18 weeks as a preventive strategy for preterm birth 1

Implementation Algorithm

1. First trimester (ideally before 12 weeks):

   • Complete risk assessment using maternal history and clinical risk factors
   • Consider additional screening with uterine artery Doppler and serum biomarkers in high-risk women
   • Start low-dose aspirin (75-150 mg daily) in high-risk women before 16 weeks

2. Early pregnancy screening:

   • Screen for asymptomatic bacteriuria before 20 weeks
   • Treat promptly if positive to prevent preterm labor

3. Throughout pregnancy:

   • Monitor fetal growth with serial fundal height measurements
   • Perform ultrasound if growth concerns arise
   • Continue aspirin until 36 weeks or delivery

Common Pitfalls to Avoid

• Starting aspirin too late: Initiating aspirin after 16 weeks significantly reduces its effectiveness in preventing preeclampsia and preterm birth 1, 3

• Inadequate dosing: Using only 60 mg aspirin when 100 mg or higher may be more effective, particularly in obese women 1, 5

• Missing asymptomatic bacteriuria: Failure to screen and treat early can increase preterm birth risk significantly 2

• Relying on sexual abstinence: No evidence supports avoiding coitus after 18 weeks as an effective strategy 1

The number needed to treat to prevent one preterm birth with low-dose aspirin is 65 (95% CI 38-455), making this a highly effective intervention with minimal risk 1.