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Chapter 1: Preterm Labor

Rupsa C. Boelig; Vincenzo Berghella

SCOPE

DISEASE/CONDITION(S)

Preterm labor (PTL) and preterm premature rupture of membranes (PPROM)

GUIDELINE OBJECTIVE(S)

Define PTL and PPROM; outline diagnosis and initial assessment of PTL and PPROM; review evidence-based management practices in PTL and PPROM including the appropriate initiation and selection of tocolytics, antibiotics, corticosteroids, and magnesium sulfate.

BRIEF BACKGROUND

Preterm birth (PTB) is one of the leading causes of neonatal morbidity and mortality. In the United States in 2013, 11.39% of all births were preterm. Neonatal complications of PTB include respiratory, gastrointestinal, and neurological difficulties as well as long-term neurodevelopmental deficits. The annual cost of PTB in the United States was estimated to be $26.2 billion in 2005. While approximately 35% of PTBs are iatrogenic for maternal or fetal indications, the majority are spontaneous preterm births (sPTB), of which 40–45% are related to preterm labor (PTL) and 25–30% are due to preterm premature rupture of membranes (PPROM). Both PTL and PPROM are considered to be part of a syndrome with multiple inciting mechanisms including inflammation, infection, uterine overdistension, uteroplacental ischemia/hemorrhage, and other immune-mediated processes that ultimately lead to PTB. In most cases, a precise mechanism or cause cannot be identified.

Risk factors for sPTB are outlined in Table 1.1; although there are a number of demographic, medical, social, and antepartum factors associated with PTB, the most significant historical risk factor is a history of a prior sPTB.

TABLE 1.1.Risk Factors for Preterm Birth
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TABLE 1.1. Risk Factors for Preterm Birth

Maternal Demographic and Social History

  • Race (African American at higher risk compared to Asian, Caucasian, and Hispanic)

  • Age ≥35 or <17

  • BMI >35 or <19

  • Tobacco use

  • Substance use disorder (opiate or cocaine)

  • Low socioeconomic status

Obstetric/Gynecologic History

  • Prior preterm birth (>20 weeks) or late second trimester loss (>16 weeks)

  • Multiple dilation and evacuations

  • History of sexually transmitted infections

  • Prior cervical surgery

  • Uterine anomaly

Current Pregnancy Characteristics

  • Short-interval pregnancy (<6 months)

  • Fetal disease: growth restriction, poly or oligohydramnios, major congenital or chromosomal anomaly

  • Assisted reproductive technologies

  • Abnormal placentation

  • Bacterial vaginosis this pregnancy

  • Vaginal bleeding

  • Maternal infection: urinary tract, sexually transmitted

  • Depression/anxiety/significant psychosocial stressors

  • Maternal medical comorbidities: hypertension, diabetes, asthma, thyroid disease

  • Abdominal surgery

  • Multiple gestations

  • Cervical length ≤25 mm between 16 and 24 weeks

DIAGNOSIS OF PRETERM LABOR

PTL has been traditionally defined by the clinical criteria of regular uterine contractions with a change in cervical dilation and/or effacement, or by the presentation of regular uterine contractions and a cervical dilation of at least 2 cm in pregnant women between 20 and 36 6/7 weeks’ gestation. Unfortunately, this clinical criteria alone has a limited positive predictive value, with >70% of women presenting in this manner ultimately delivering at term. A more accurate definition may be ...

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