SUMMARY:

Spontaneous preterm birth (PTB) includes preterm labor, preterm rupture of membranes and cervical insufficiency <37 weeks of gestation. The PTB rate has significantly increased during the last 2 decades. According to the CDC, PTB rates decreased from 2007 to 2014, partly due to fewer teens and young women giving birth. However, the PTB rate rose for the fifth year in a row in 2019 and sits at approximately 10%. Unfortunately, racial, and ethnic differences in PTB rates remain problematic. The CDC reports that “in 2019, the rate of preterm birth among non-Hispanic black women (14.4%) was about 50% higher than the rate of preterm birth among non-Hispanic white women (9.3%) or Hispanic women (10%).”

Adverse Outcomes and Preterm Birth

• The rate of neonatal adverse outcomes decreases with advancing gestational age
  • While adverse outcomes are therefore greatest <34 weeks (early preterm), higher rates of both short- and long-term complications are seen between 34w0d an 36w6d (late preterm) vs ≥37 weeks
• The CDC reported that in 2018, preterm birth and low birth weight accounted for about 17% of infant deaths <1 year
• Associated adverse outcomes include
  • Respiratory complications | Feeding difficulties | Cerebral palsy | Developmental delay | Vision and hearing impairment

Risk Factors 

• History of prior PTB
  • Number of prior preterm birth deliveries
  • Gestational age at delivery
• Short cervical length (<25 mm)
• Behavioral factors
  • Low maternal pre-pregnancy weight (BMI <19.8)
  • Smoking
  • Substance abuse
  • Short interpregnancy interval

Screening Modalities 

• Transvaginal (not abdominal) cervical length
• Not recommended
  • Fetal fibronectin testing
  • Bacterial vaginosis testing
  • Home contraction monitoring

Clinical Evaluation and Management

Previous Spontaneous PTB

• Risk assessment
  • Detailed medical history and prior obstetric history
• Management
  • Progesterone starting at 16 to 24 weeks
  • Serial transvaginal cervical length measurements every 2 weeks from 16 to 23 weeks
  • PTB <34 weeks and cervical length less than 25 mm: Cervical cerclage (see more on cerclage recommendations in ‘Related ObG Topics’ below)

No Previous History of PTB

• Low risk for PTB
  • Universal second trimester cervical length can be considered
• Cervical length <20mm
  • Daily vaginal progesterone: Reduces risk of PTB
    • Vaginal micronized suppository 200 mg or
    • Vaginal gel 90mg
  • Cervical cerclage: No significant reduction of PTB
  • Pessary: Literature has demonstrated potential benefit in smaller studies, but requires confirmation prior to recommending use to prevent PTB in this population

Multiple gestation with or without history of PTB

• Progesterone: No reduction of PTB
• Cerclage if cervix <25 mm: May increase risk for PTB

KEY POINTS:

• Women with singleton pregnancy and history of PTB should be offered progesterone supplementation staring at 16 to 24 weeks
• Vaginal progesterone is recommended in women without a history of PTB but with short cervix (<20mm)
• Screening for fetal fibronectin, bacterial vaginosis and home contraction monitoring are not recommended
• Universal cervical length may be considered
• Neither progesterone nor cerclage are recommended in multiple gestations

Learn More – Primary Sources:

ACOG Practice Bulletin 130: Prediction and Prevention of Preterm Birth

CDC: Premature Birth

Related ObG Topics:

Cervical Cerclage – Professional Recommendations

FDA, SMFM and ACOG Respond to PROLONG Study Results: Does IM 17-OHPC Impact Preterm Delivery?

Antenatal Corticosteroids – When to Administer?

Does fetal fibronectin testing prevent preterm birth?

Progesterone or Cerclage in Preterm Prevention in Women with Previous Preterm Birth and Short Cervix?

Can Cervical Pessaries Prevent Preterm Birth?