Antepartum Fetal Surveillance

Antepartum
Fetal Surveillance

      

• SP
  Chauhan, SF Charania, RA McLaren, et al (Med College
  of Georgia, Atlanta; Univ Illinois, Peoria; Univ of
  Mississippi, Jackson)
  
  
  Ultrasonographic Estimate of Birth Weight at 24 to
  36 Weeks: A Multicenter Study.
  
  
  Am J Obstet Gynecol 179: 909-916, 1998.
  
   
  
  
  Background: A method for reliably estimating fetal
  weight in preterm labor with eventual preterm
  delivery would be useful. The accuracies of U.S.
  estimates of birth weights among infants born
  between 24 and 34 weeks’ gestation at 3 centers were
  determined.
  
    
  
  
  Data on 171 fetuses at each center were analyzed.
  
  Prediction limit calculation showed that fetal
  weight estimates of more than 1,600g, more than
  1,900g, and more than 1800g at the 3 centres,
  respectively, were required to predict actual
  weights of more than 1500g with a 70% accuracy.
  
    
  
  
  Christine Comstock, MD., Assistant Professor, Wayne
  State University comments: Accurate estimates of
  fetal weight can be very useful in clinical decision
  making in the preterm labor patient. There are a
  number of methods of estimating weight by
  ultrasonography. All involve ultrasonographic
  measurement of at least 2 of the following
  parameters: biparietal diameter, head circumference,
  femur length, and abdominal circumference. 
  
    
  
  
  In general, an estimate should be within ±10% in
  90% of estimates, although in macrosomic fetuses
  most formulas perform less well. The abdominal
  circumference, which is used in almost all formulas,
  is measured by tracing the abdomen at the level of
  curvature of the hepatic vein in a plane exactly
  perpendicular to the spine and includes the actual
  skin line. If the fetus is breathing or if it is
  lying against the uterine wall or if there is little
  amniotic fluid, the skin line is not stable or
  cannot be seen well.
  
    
  
  
  The 24 to 34 weeks window is the one in which most
  centers have been successful in predicting weight in
  the absence of ruptured membranes. Amniotic fluid is
  most plentiful during those weeks, providing a clear
  outline of the abdomen, and macrosomia is rarely
  present. This is the window when a carefully
  obtained weight estimate should be expected to be
  within ± 10% in most cases.
  
    
  

• L
  Verma, F Macdonald. P Leedham, et al (Birmingham
  Heartlands Hosp, England)
  
  
  Rapid and Simple Prenatal DNA Diagnosis of Down’s
  Syndrome.
  
  
  Lancet 352: 9-12, 1998.
  
    
  
  
  Since the 1970s, cultured amniotic fluid cells
  obtained by amniocentesis at around 16 weeks of
  gestation have been used for the prenatal diagnosis
  of down’s syndrome by Karyotyping. This approach
  requires 10 mL of fluid, and it takes an average of
  15 days for the results to be known. A new approach
  involves polymerase chain reaction (PCR)
  amplification of small-tandem-repeat markers located
  on chromosome 21 and analysis with fluorescence
  based methods. With this technique, results are
  available on the same day and only a small amount of
  fluid is required. The use of this approach for the
  diagnosis of trisomy 21 was investigated in a series
  of more than 2000 samples of amniotic fluid
  
    
  
  
  Two DNA markers gave an informative and correct
  result in 2,083 of 2,139 samples (97.4%), in which
  30 fetuses were identified as having trisomy 21
  Down’s syndrome and 2,053 fetuses were identified as
  normal. In 32 of 41 other clear samples, an extra
  marker was informative. With these 3 markers, a
  total of 99.6% informative results were achieved. No
  false negative or false positive results were seen.
  
    
  
  
  Authors conclude -For improved prenatal diagnosis of
  Down’s syndrome, the PCR-based DNA diagnostic test
  has great potential. The advantage is that results
  may be available within a day.
  
    
  
  
  The PCR has revolutionized the practice of molecular
  genetics. Similar techniques could be employed
  simultaneously for the prenatal diagnosis of other
  common aneuploidies such as trisomy 13 and trisomy
  18. PCR based prenatal diagnosis of trisomy 21 (as
  an adjunct to conventional cytogenetic analysis) is
  cost-effective and that the tremendous time saving.
  Rapid prenatal diagnosis of trisomy 21 through
  fluorescence in situ hybridization (FISH) is already
  a relatively well-established procedure in the
  United States.
  
      

• MJ
  Hussey, ES Levy, et al (Rush-Presbyterain-St.Luke’s
  Med Ctr, Chicago)
  
  
  Evaluating Rapid Diagnostic Tests of Intra-amniotic
  Infection: Gram Stain, Amniotic Fluid Glucose Level,
  and Amniotic Fluid to Serum Glucose Level Ratio.
  
  Am J Obstet Gynecol 179:650-656, 1998.
  
    
  
  
  After studying one hundred twenty-seven patients in
  preterm labor and 26 with preterm premature rupture
  of the membranes, the authors came to the conclusion
  that the diagnostic values of amniotic fluid glucose
  and the ratio of amniotic fluid to serum glucose
  were equivalent. However, Gram stain is superior to
  both. Combining Gram stain with amniotic fluid
  glucose level is superior to any individual test.
  
    
  

• Ymd
  Lo, NM Hjelm, C Fidler, et al (Univ of Hong Kong,
  China; John Radcliffe Hosp, Oxford, England)
  
  
  Prenatal Diagnosis of Fetal RhD Status by Molecular
  Analysis of Maternal Plasma.
  
  
  N Engl J Med. 339: 1734-1738, 1998.
  
    
  
  
  Rhesus (Rh) isoimmunization still occurs, despite
  the widespread use of Rh immune globulin prophylaxis
  in RhD negative pregnant women. It would be useful
  to determine the RhD status of these infants because
  no further testing or therapeutic procedures would
  be necessary if the infants were RhD-negative. The
  feasibility of fetal RhD genotyping with the use of
  fetal DNA extracted from plasma samples from RhD
  negative pregnant women was assessed.
  
     
  
  
  Method: The study included 57 RhD negative pregnant
  women and their singleton fetuses: 12 were in their
  first trimester; 30 were in their second trimester;
  and 15 were in their third trimester. An analysis
  was conducted for the RhD gene with a PCR test
  sensitive enough to detect the RhD gene in a single
  cell from DNA extracted from maternal plasma.
  Serologic analysis of cord blood or PCR analysis of
  amniotic fluid was used to determine fetal RhD
  status.
  
     
  
  
  Results : The results of RhD PCR analysis of
  maternal plasma DNA were completely concordant with
  the results of serologic analysis in the samples
  obtained from women in their second or third
  trimester of pregnancy. Two of the maternal plasma
  samples collected in the first trimester contained
  no RhD DNA, but the fetuses were RhD-positive. The
  other 10 samples were found to be concordant; 7 were
  RhD-positive and 3 were RhD negative.
  
    
  
  
  Conclusion: Noninvasive fetal RhD genotyping can be
  performed rapidly and reliably with the use of
  maternal plasma at the beginning of the second
  trimester of pregnancy. Not only is the method is
  reliable but also rapid.
  
    

• TD
  Shipp, BR Benacerraf (Massachusetts General
  Hospital, Boston; Brigham and Women’s Hospital,
  Boston; Harvard Med School, Boston)
  
  
  The Significance of Prenatally Identified Isolated
  Clubfoot: Is Amniocentesis Indicated?
  
  
  Am J Obstet Gynecol 178:600-602, 1998.
  
    
  
  
  Most fetuses with clubfoot have other malformations,
  often associated with karyotypic abnormalities.
  
    
  
  
  Patients: The 9-year review included 87 fetuses with
  isolated clubfoot identified on prenatal Ultrasound.
  Follow-up information was available on 68 fetuses.
  At birth, 38 fetuses were correctly identified as
  having bilateral clubfoot and 15 as having
  unilateral clubfoot. Eight fetuses with a ultrasound
  diagnosis of clubfoot were found to be normal at
  birth. In utero karyotyping was performed on 34
  fetuses, 4 of which had abnormal karyotypes. The
  abnormal karyotypes identified were 47 XXY, 47 XXX
  trisomy 18, and trisomy 21.
  
     
  
  
  The authors conclude that a 6% incidence of
  karyotypic abnormalities among fetuses with a
  ultrasound finding of isolated clubfoot was found.
  These fetuses should be karyotyped even if clubfoot
  is the only apparent congenital anomaly. Ultrasound
  used prenatally for the detection of clubfoot has a
  false-positive rate of 12%; the false-negative rate
  is unknown.
  
     
  
  
  Budorick et al report on the value of 3-dimensional
  ultrasound of the fetal distal lower extremity,
  normal and abnormal. Three-dimensional ultrasound
  improves one’s ability to evaluate the lower limb.
  
     
  

• AG
  Hadley, A Wilkes, et al (Internatl Blood Group
  Reference Lab, Bristol, England; The Bristol Blood
  Centre, England; St. Michael’s Hosp, Bristol,
  England)
  
  
  The Ability of the Chemiluminescence Test to Predict
  Clinical Outcome and the Necessity for Amniocenteses
  in Pregnancies at Risk of Haemolytic Disease of the
  Newborn.
  
  Br. J Obstet Gynaecol 105: 231-234, 1998.
  
     
  
  
  The results of the study show that chemiluminescence
  testing was better correlated with the clinical
  outcome of hemolytic disease than was AutoAnalyzer
  testing. Chemiluminescence correctly identified 94%
  of unaffected fetuses, compared with 73.5% with the
  AutoAnalyzer. Prediction of severely affected cases
  were 97% vs.85% respectively. Neither test correctly
  distinguished unaffected from mildly affected cases.
  
      
  
  
  Comments: The first step is to establish antibody
  levels in maternal serum to determine if
  amniocentesis or percutaneous umbilical cord
  sampling is indicated. Traditionally, anti-D levels
  have been measured by AutoAnalyzer, but cellular
  assays such as the chemiluminescence test (CLT)
  measure the biological activity of the antibodies;
  thus, they should be more reliable.