Surveillance

Surveillance
   

• The Natural History of Fetomaternal Alloimmunization to the Platelet specific Antigen HPA-1a as Determined by Antenatal Screening. 
  LM Williamson, et al (Univ of Cambridge, England; East Anglia and Birmingham Centres, England; Addenbrooke’s Hosp, Cambridge, England; et al). 
  Blood 92:2280-2287,1 998.
  
  The most common cause of severe fetal and neonatal thrombocytopenia is immunization against the human platelet antigen (HPA)-1 alloantigen. Fetal therapy is associated with significant risks, and this study clarified the indications for treatment.
      
  Conclusion: 1 in 350 unselected pregnancies is complicated by HPA-1a alloimmunizaiton. This complication results in severe thrombocytopenia in 1 in 1200 through HPA-1a and HLA-DRB3 0101 typing combined with antiHPA-1A, titration. Clinicians can identify most pregnancies at risk of severe thrombocytopenia.
      
  Editorial comments: Alloimmune thrombopenia based on maternal antibody production, usually stimulated by human platelet antigen 1A(HPA-1a) born on fetal platelets and absent in maternal blood, usually appears in the form of fetal haemorrhage in an earlier pregnancy. Genotyping for HLA-DRB3 0101, a gene thought to be predictive of alloimmune sensitization was carried out along with serial assays of HLA-1A antibody. 
       
  The only predictor of severe newborn thrombocytopenia of interest was a maternal antibody titer greater than 1 to 32 in a third-trimester pregnancy. Although HLA genotyping for prediction of severity had a specificity of 99%, the prospective value of a positive finding was 35% with a 65% false positives. 
      
  This data confirms the lack of cost effectiveness of routine HPA testing in pregnant women but point to some area where future refinements could increase efficacy of therapy using maternal immunoglobulinG or fetal platelet transfusion.
      

• Effect of Antenatal Betamethasone Administration on Placental Vascular Resistance. 
  EM Wallace, LS Baker (Monash Univ, Clayton, Australia, Monash Med Centre, Clayton, Australia) 
  Lancet 353; 1404-1407, 1999.
      
  In a population of 28 women with median gestational age of 27 weeks, absent end-diastolic flow velocity (AEDF) on umblical artery Doppler examination was confirmed. Roughly, 2/3rd of the these women had return of diastolic flow velocity after betamethasone administration in the customary dosage used for fetal pulmonary maturation. At the same time all 21 women with pregnancy induced hypertension received a variety of antihypertensive agents such as labetol, nifedipine and methyl-dopa without regular pattern. No relationship between altered umbilical artery Doppler findings and pregnancy complications or antihypertensive medications were noted. 
      
  Those who believed that AEDF is related to structural change in the umblical circulation believed that “the underlying vascular lesion impaired flow of AEDF, is a irreversible and progressive process”. Because that is clearly not true in light of this observation, it casts doubt on the conventional view of the origin of AEDF.
     

• Eric H Dellinger, Frank H Boehm and Martin M Crane, (Division of Maternal-Fetal Medicine, Department of Obstetrics & Gynecology, Greenville)
  Electronic fetal heart rate monitoring: Early neonatal outcomes associated with normal rate, fetal stress, and fetal distress.
  Am J Obstet Gynecol, Jan.2000, vol.182(1), Part I, 214-220.
     
  The introduction of electronic fetal monitoring into the practice of obstetrics has profoundly altered the face of the specialty. Nearly 40 years later, electronic fetal monitoring commands a near universal presence in labor and delivery suites in the United States, but debate continues as to whether its use has been a positive or negative factor in modern medical practice.
      
  Although logic would seem to dictate that continuous fetal monitoring should be superior to intermittent auscultation, the medical literature has produced conflicting results regarding neonatal outcomes when these 2 modalities are compared. Some studies have demonstrated improved neonatal outcome with electronic fetal monitoring, whereas other studies have shown no improvement with respect to intermittent auscultation.
      
  What appears to be free from dispute is the startling statistic that cesarean delivery rates quadrupled in the 3 decades since electronic fetal monitoring was first adopted into clinical practice. Parallel with these rising abdominal delivery rates has been an increased use of the diagnosis of fetal distress in the absence of an increase in adverse neonatal outcome. The resulting implication is that electronic fetal monitoring interpretation is inconsistent, is at time inaccurate, may fail to predict neonatal outcome, and is subject to influence by the medicolegal climate.
      
  The purpose of this study was to test the ability of a well-defined classification system for electronic fetal heart rate (FHR) tracings to predict early neonatal outcome. Tracings were defined either as being normal, as exhibiting fetal distress, or as showing signs of an intermediate fetal condition labeled fetal stress. Fetuses with each category of tracing were compared with respect to Apgar scores, umbilical cord blood gases, and admission to the neonatal intensive care unit.
      
  Study Design: All labors of women with singleton pregnancies ³32weeks’ gestation electronically monitored at 2 institutions were examined. Tracings in the final hour before delivery were defined as normal, fetal stress, or fetal distress. After delivery, Apgar scores, cord blood gas values, and admission to the neonatal intensive care unit were examined as measures of early neonatal outcome.
      
  Results: Among the 898 patients who qualified for study, 627(70%) had tracings classified as normal, 263 (29%) had tracings classified as fetal stress, and 8(1%) had tracings classified as fetal distress. There was a significant worsening of neonatal outcome across these 3 groups with regard to depressed Apgar scores 1 minute (5.1%, 18.3%, and 75.0%; P, 05), depressed Apgar scores at 5 minutes (1.0%, 3.8%, and 37.5%; P, 05), and admission to the neonatal intensive care unit (5.6%, 10.6%, and 37.5%; P< .05). There was also a progressive worsening of cord blood pH (7.27 ± 0.06, 7.21 ± 0.08, and 7.06 ± 0.14; P< .05), a progressive increase in Pco2 (53.39 ± 10.55mm Hg, and 78.31 ± 20.35 mm Hg; P <>05), and a progressive decline in base excess (-3.18 ± 2.02 mEq/L, -5.11 ± 3.11 mEq/L, and -9.07 ± 4.59 mEq/L; P <. 05).
      
  Conclusion: This simple classification system for interpreting fetal heart rate tracings accurately predicts normal outcomes for fetuses as well discriminating fetuses in true distress. Further, it identified an intermediate group of fetuses with a condition labeled fetal stress who might benefit from additional evaluation and possibly from expeditious delivery.