Medical brain notes 42

  Preterm Labor   Preterm birth  is delivery that occurs prior to the P  completion of 37 weeks (259 days) of gestation.   Because it is the most common cause of perinatal morbidity and mortality in the United States,  prevention and treatment of preterm birth is a major focus of obstet-ric care.   The consequences of preterm birth occur with increasing severity and frequency the earlier the gesta-tional age of the newborn. In addition to perinatal death in the very young fetus, common complications of preterm birth include respiratory distress syndrome, intraven-tricular hemorrhage, necrotizing enterocolitis, sepsis, neurologic impairment, and seizures. Long-term mor-bidity associated with preterm delivery includes broncho-pulmonary dysplasia and developmental abnormalities, including cerebral palsy.  The 11% to 12% of babies bornprematurely account for 75% of all perinatal mortality and 50% of long-term neurologic impairment in children in the United States.   Preterm births may be c

  Causes   Preterm labor may represent a final common pathway for a number of pathogenic processes. The four main processes include: (1) activation of the maternal or fetal hypothalamic-pituitary-adrenal axis due to maternal or fetal stress,   decidual-chorioamniotic or systemic inflammation caused by infection, (3) decidual hemorrhage, or (4) patho-logic uterine distention (Fig. 20.1). Numerous risk factors have been associated with preterm labor (Box 20.1).  Thestrongest risk factor is multifetal gestation.  With a priorpreterm birth, the risk in a subsequent pregnancy increases and continues to increase with each subsequent pregnancy. African-American women have higher rates of preterm birth associated with preterm labor or preterm PROM, compared with other racial and ethnic groups. Subclinical intra-amniotic infection has also been associated with preterm labor and preterm PROM, especially when it oc-curs at earlier gestational ages.  In most cases, however, no causeor risk factor

  EVALUATION OF A PATIENT IN SUSPECTED PRETERM LABOR   Prompt evaluation is critical in the patient who describes symptoms and signs suggestive of preterm labor. Use of an external electronic fetal monitor ( tocodynamometer ) may help to quantify the frequency and duration of con-tractions. The status of the cervix should be determined, either by visualization with a speculum or by gentle digi-tal examination. Because digital examination may increase the risk of infection in the setting of PROM, speculum evaluation to assess cervical dilation and effacement should be performed first if there is suspicion of rupture of fetal membranes. Changes in cervical effacement and dilation on subsequent examinations are important in the evalua-tion of both the diagnosis of preterm labor, as well as the effectiveness of management.  Subtle changes are often of greatclinical importance, so serial examinations by the same exam-iner are optimal, when this is possible.   Because urinary infections can

  MANAGEMENT OF PRETERM LABOR   The purpose in treating preterm labor is to delay delivery, if possible, until fetal maturity is attained.   Management involves two broad goals: (1) the detection and treatment of disorders associated with preterm labor, and (2) therapy for the preterm labor itself.  Fortunately,more than 50% of patients with preterm contractions have spontaneous resolution of abnormal uterine activity.  However,this complicates the evaluation of effectiveness of specific treatments, because it is unclear if the contractions would have resolved spontaneously or if their cessation was due to effective treatments.   Various tocolytic therapies have been used in the management of preterm labor (Table 20.1). Tocolytics have not been shown to prolong pregnancy beyond sev-eral days (only 2 to 7). Different treatment regimens ad-dress specific mechanisms involved in the maintenance of uterine contractions, and each, therefore, may be best suited for certain patients. Typically