• Clinical science

Preterm labor and birth

Abstract

Preterm labor is defined as regular uterine contractions and cervical changes before 37 weeks of pregnancy. Preterm birth is defined as live birth between 20 0/7 weeks and 36 6/7 weeks of gestation. Approximately half of patients who deliver prematurely are diagnosed with preterm labor. Risk factors include a previous preterm birth, a short cervical length during pregnancy, and multiple gestation. Clinical features include early onset of contractions, premature cervical changes, or premature rupture of membranes. The diagnosis is usually clinical and can be supported by a cervical ultrasound and/or fetal fibronectin detection test. Treatment includes tocolysis, antenatal steroids to improve fetal lung maturity, and magnesium sulfate to provide fetal neuroprotection. Tocolytic agents are used to prolong pregnancy to gain time for steroids and magnesium sulfate to take effect. Complications of the preterm child include intraventricular hemorrhage, respiratory distress syndrome, and necrotizing enterocolitis. Avoidance of modifiable risk factors, management of cervical insufficiency, and vaginal progesterone supplementation can help prevent preterm labor in certain risk groups.

Definition

  • Preterm labor: Regular uterine contractions with cervical effacement, dilation, or both before 37 weeks gestation.
  • Preterm birth
    • Live birth between 20 0/7 weeks and 36 6/7 weeks of gestation
    • WHO subcategories
      • Extremely preterm (< 28 weeks)
      • Very preterm (28 to < 32 weeks)
      • Moderate to late preterm (32 to < 37 weeks)

References:[1][2]

Epidemiology

  • Complications of preterm birth are the leading cause of death in children < 5 years of age worldwide
  • Approximately half of patients who deliver prematurely are diagnosed with preterm labor.
  • Preterm birth rate in the US: approx. 12% of all live births

References:[1][3][4][5]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

The exact pathogenesis of premature labor is not well understood, but it is associated with certain risk factors.

References:[6][7][8][9]

Clinical features

References:[5]

Diagnostics

  • Clinical diagnosis based on preterm contractions and cervical changes (see also “Childbirth”)
  • Supportive tests
    • Transvaginal cervical ultrasound: for diagnosis of short cervix
    • Cervicovaginal fetal fibronectin detection test: a positive test supports the diagnosis of preterm labor

References:[5]

Treatment

Antibiotics for group B streptococcus (GBS) prophylaxis is recommended in preterm labor, preterm premature rupture of membranes and when GBS infection is evident!

References:[10][11][5][12][6869]

Complications

The general immaturity of premature organ systems leads to various complications in the preterm infant: e.g., immature lungs may develop bronchopulmonary dysplasia and immature central nervous system structures may develop intracranial hemorrhage.

Morbidity and mortality in preterm infants increase with decreasing birth weight and gestational age!


References:[13][14][15]

We list the most important complications. The selection is not exhaustive.

Prevention

  • Mothers should avoid modifiable risk factors (see “Etiology” section above)
  • Manage cervical insufficiency, if present (see “Complications” section in “Pregnancy”)
  • Vaginal progesterone supplementation
    • Women with a singleton pregnancy at 16–24 weeks gestation with a prior singleton preterm birth, regardless of cervical length and/or cervical cerclage
    • Women ≤ 24 weeks gestation with a short cervical length (≤ 25 mm)

References:[8]