Diagnosis of Preterm Labor and Overview of Preterm Birth

Diagnosis of preterm labor and overview of preterm birth Author: Charles J Lockwood, MD, MHCM Section Editor: Susan M Ramin, MD Deputy Editor: Vanessa A Barss, MD, FACOG Contributor Disclosures

All topics are updated as new evidence becomes available and our peer review process is complete. Literature review current through: Jan 2017. | This topic last updated: Feb 17, 2017. INTRODUCTION — Identifying women with preterm contractions who will actually deliver preterm is an inexact process, even though preterm labor is one of the most common reasons for hospitalization of pregnant women. Accurate identification of women truly in preterm labor allows appropriate application of interventions that can improve neonatal outcome: antenatal corticosteroid therapy, group B streptococcal infection prophylaxis, magnesium sulfate for neuroprotection, and transfer to a facility with an appropriate level nursery (if necessary). On the other hand, accurate triage of women not actually in preterm labor can avoid performance of unnecessary interventions and associated costs for the 20 to 50 percent of patients with suspected preterm labor who will go on to deliver at term without tocolytic therapy [1]. This topic will describe our approach to the diagnostic evaluation of women who present with possible preterm labor and provide an overview of issues related to preterm birth. Treatment of preterm labor is discussed separately. (See "Inhibition of acute preterm labor".) PRETERM LABOR Pathogenesis — The pathophysiology of preterm labor involves four primary pathogenic processes that result in a final common pathway ending in spontaneous preterm labor and delivery: ●Activation of the maternal or fetal hypothalamic-pituitary-adrenal axis associated with either maternal anxiety and depression or fetal stress ●Infection ●Decidual hemorrhage ●Pathological uterine distention These processes and the pathophysiology of normal labor are discussed in detail separately. (See "Pathogenesis of spontaneous preterm birth" and "Physiology of parturition".) Clinical findings — The clinical findings of true labor (ie, contractions plus cervical change) are the same whether labor occurs preterm or at term. The following are early signs and symptoms of labor; however, they are non-specific and can be present for several hours in women who do not exhibit cervical change: ●Menstrual-like cramping ●Mild, irregular contractions

●Low back ache ●Pressure sensation in the vagina ●Vaginal discharge of mucus, which may be clear, pink, or slightly bloody (ie, mucus plug, bloody show) Uterine contractions are the sine qua non of labor, but mild irregular contractions are a normal finding at all stages of pregnancy, thereby adding to the challenge of distinguishing true labor (contractions that result in cervical change) from false labor (contractions that do not result in cervical change, ie, Braxton Hicks contractions). True labor is more likely when an increasing frequency of contractions is accompanied by increasing intensity and duration of contractions as an increase in the frequency of contractions alone may occur transiently, especially at night and with increasing gestational age. Although many investigators have tried, no one has been able to identify a threshold contraction frequency that effectively identifies women who will progress to true labor. Only 13 percent of women presenting at