Impending Premature Birth: Prevention

To prevent threatened preterm birth, attention must be paid to reducing risk factors.

These measures, which are started before or during pregnancy and are effective, are called primary prevention in contrast to secondary prevention, which involves prophylactic therapeutic measures after an increased risk has been identified during prenatal care.

Primary prevention

Behavioral risk factors

  • Diet
  • Pleasure food consumption
    • Alcohol (> 20 g/day)
    • Tobacco (smoking)
  • Drug use
    • Cannabis (hashish and marijuana) – with persistent cannabis use during pregnancy, adjusting for the influence of smoking, alcohol, age, and socioeconomic status, the adjusted odds ratio was 5.44 for preterm birth (95 percent 2.44 to 12.11), ie, was associated with a fivefold increased risk.
  • Physical activity
    • High physical load
  • Psycho-social situation
    • Chronic stress
  • Overweight (BMI ≥ 25; obesity).
  • Underweight

Progesterone administration for primary prevention

Studies support the benefit of progesterone administration for the following patients:

  • Singleton pregnancy in postpreterm delivery condition. Onset: 16+0 weeks of gestation (SSW) – 36+0 SSW.
  • Pregnant women with cervical shortening < 25 mm in the 20 – 22 SSW to 36+0 SSW.

By far the most effective procedure proved to be intravaginally applied progesterone in doses between 90 and 400 mg daily. This resulted in a reduction of preterm births before 34 SSW compared to preterm births among women in the control groups by about 60% and births before 37 weeks by about 70%. Furthermore, the number of deaths among newborns decreased by 60%.

According to the current S2k guideline “Prevention and Therapy of Preterm Birth”, these pregnant women should receive daily vaginal progesterone (e.g., 200 mg capsule) until 36+6 SSW [guidelines: S2k guideline].

(There is no benefit for pregnant women with multiple pregnancies or premature rupture of membranes).

Secondary prevention

The goal is to prevent preterm delivery by taking appropriate measures. These include:

  • Vaginal pH measurement (if pH > 4.4, acidification with lactobacilli or local antibiotic therapy).
  • Vaginal sonographic cervical measurement (cervical length measurement); If the cervical length ≤ 25 mm before the 24th week of pregnancy, progesterone substitution until 36+0 SSW and additionally possibly a cerclage, a complete cervical closure or the insertion of a cerclage pessary (Cervixpessar).

Cervical pessaries reduced the preterm birth rate before 37 weeks gestation by 70%.

For cerclage, which involves placing a nonabsorbable band around the cervix, there was no prevention success in any subgroup or endpoint.