Subclinical Infection And Cytokines In Preterm Birth

Child Health And Human Development

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Abstract

Premature birth is the leading cause of perinatal mortality and morbidity worldwide. The Perinatology Research Branch has defined preterm labor as a syndrome and determined that at least 25% of preterm neonates are born to women with sub-clinical intrauterine infection. Moreover, the Branch has provided evidence that many premature neonates are critically ill before birth and proposed that, in the context of intrauterine infection, the onset of premature labor has survival value. The goal of this project is to understand the pathophysiology of premature labor and delivery and the focus of our research this year was to study the frequency of intra-amniotic infection in women presenting with vaginal bleeding during pregnancy, the role of complement activation in the Great Obstetrical Syndromes, as well as the clinical value of cervical sonography and fetal fibronectin in the prediction of spontaneous preterm birth. 1. The frequency and clinical significance of microbial invasion of the amniotic cavity (MIAC) in patients with vaginal bleeding. Vaginal bleeding is one of the most common complications of pregnancy. Yet, the causes of this complication remain largely unexplained, although its presence is a risk factor for adverse pregnancy outcome (e.g., preterm premature rupture of membranes, intrauterine growth restriction, etc.). The Branch conducted a retrospective cohort study of women who presented with vaginal bleeding between 18 and 35 weeks, and who had undergone amniocentesis for the assessment of the microbiologic status of the amniotic cavity and/or fetal lung maturity. MIAC was detected in 14% of cases. Patients with vaginal bleeding and a gestational age less than 28 weeks at the time of amniocentesis had a significantly higher frequency of MIAC than those with a gestational age 28 weeks. Ureaplasma urealyticum was the microorganism most frequently isolated from the amniotic fluid. Except for one case admitted at 33 weeks, all patients with MIAC had an early preterm delivery less than or equal to 32 weeks. Patients with vaginal bleeding and MIAC had a shorter procedure-to-delivery interval than those without MIAC. These observations suggest that vaginal bleeding may be the only clinical manifestation of MIAC, and it predisposes to adverse outcome. 2. A short uterine cervix is a risk factor for MIAC in women presenting with preterm labor and intact membranes. Women with MIAC are at greater risk for adverse outcome. However, MIAC is sub-clinical in nature and identification requires the performance of an amniocentesis. This study was conducted to determine if women who present with preterm labor and a short cervix determined by sonographic examination had a higher rate of culture-proven MIAC than those without a short cervix. Ultrasonography and amniocentesis were performed in 401 patients admitted with preterm labor (22-35 weeks) and cervical dilatation of less than or equal to 3 cm, as assessed by digital examination. The prevalence of MIAC was 7% (28/401). Patients with a cervical length less than 15 mm had a higher rate of a positive amniotic fluid culture than patients with a cervical length greater or equal to 15 mm. Forty percent of patients had a cervical length greater or equal to 30 mm. These patients had a very low risk of MIAC, spontaneous delivery less than or equal to 35 weeks, within 7 days, and within 48 hours of admission. This study suggests that endovaginal ultrasonographic examination of the uterine cervix is useful in the identification of women at risk for intrauterine infection. 3. The combination of fetal fibronectin and cervical ultrasound improves the prediction of preterm delivery in patients with preterm labor and intact membranes. Vaginal fetal fibronectin and cervical ultrasound are widely used to assess the risk of preterm delivery in the United States and Europe. A critical question is whether the combined use of these two tests improves the prediction of preterm birth. A study was conducted in which ultrasound and fetal fibronectin were determined in 215 patients admitted with preterm uterine contractions (22-35 weeks) and cervical dilatation of less than or equal to 3 cm. Both tests performed comparably in the prediction of spontaneous preterm delivery. However, when fetal fibronectin results were added to those of cervical length (<30 mm), a significant improvement in the prediction of preterm delivery was achieved. Thus, we concluded that fetal fibronectin adds prognostic information to that provided by sonographic measurement of the cervical length in patients with preterm uterine contractions and intact membranes. 4. The role of complement activation in normal pregnancy and pregnancy complications. Although pregnancy has been characterized as an anti-inflammatory state thought to be beneficial for the survival of the fetal semi-allograft, many investigators believe that pregnancy is characterized by ?activation of the innate immune system? to compensate for impaired adaptive immunity and to protect the mother from infection. The complement system, a major component of innate immunity, has been recently implicated in the mechanisms of fetal loss and placental inflammation in the anti-phospholipid antibody syndrome. Inhibition of complement has been proposed as an absolute requirement for normal pregnancy. The PRB conducted a series of studies to determine the behavior of complement split products or anaphylatoxins (C3a, C4a, C5a) in normal pregnancy and pregnancy complications (preterm labor, pyelonephritis, unexplained preterm birth). The following observations were made: a) the median concentrations of C3a, C4a and C5a was significantly higher in normal pregnant women than in non-pregnant women, suggesting that normal pregnancy is associated with complement activation; b) the median plasma concentration of C5a in patients with fetal death was higher than that of normal pregnant women. This implicates complement as a potential mechanism for fetal death in humans; c) women in preterm labor with intra-amniotic inflammation had higher concentrations of C5a than women with preterm labor without MIAC. However, spontaneous labor at term was associated with a lower median concentration of maternal plasma C5a; d) pyelonephritis during pregnancy (a condition frequently associated with acute RDS was characterized by increased plasma concentrations of C5a but not other anaphylatoxins. This suggests that an excess of C5a can predispose pregnant women to develop acute RDS and multi-organ failure when affected by pyelonephritis, a common complication of pregnancy. This finding may have clinical implications since blocking C5a may improve acute RDS in experimental sepsis.