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PRENATAL CARE : SUBSEQUENT VISITS Part 02

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Maternal Serum Screen (MSS or Triple Screen)

  1. offers a risk estimate of whether the fetus may be affected with Downís
    syndrome, trisomy 18, or a NTD
  2. to make accurate diagnosis, positive MSS should be followed up with U/S and/or amniocentesis
  3. three markers
MSAFP (Maternal Serum Alpha-Fetoprotein Screening)
Beta hCG,
uE3 (Maternal estriol)
  • Trisomy 21: high Beta hCG, low MSAFP, low uE3
  • Trisomy 18: low Beta hCG,low MSAFP, low uE3

  4.  differential diagnosis of high MSAFP
  • wrong gestational age
  • > 1 fetus (e.g. twins)
  • fetal demise (death of the baby in utero)
  • NTD
  • abdominal wall defects (e.g. omphalocele)
  5.  differential diagnosis of low MSAFP
  • GTN
  • incorrect GA
  • missed abortion
  • chromosomal anomalies (e.g. Trisomy 18, 21)

   6.  80% of Downís babies born to women under 35 years, so MSS is a valuable screening tool

  7.  MSS has a 6-7% false positive rate

  8.  detection rate of Trisomy 21 with the 3 markers is 2-3 times higher than with MSAFP alone, however will still miss 20-30% of Trisomy 21 pregnancies in older women and will not reliably detect other chromosomal anomalies that occur more frequently in older women so amniocentesis should still be offered to high risk women


Group B Streptococcus

  1. danger of vertical transmission (neonatal sepsis, meningitis or pneumonia)
  2. indications for antibiotic prophylaxis (intrapartum ampicillin or clindamycin in pen-allergic - guidelines controversial)
  • positive GBS screen based on vaginal cultures taken at 36-38 weeks or
  • GBS status unknown and one of the following risk factors

    • previous GBS bacteriuria even if treated
    • previous infant with GBS infection
    • preterm labour
    • PROM > 12 hours
    • maternal intrapartum temperature > 37.7C
    • fetal tachycardia

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PRENATAL CARE : SUBSEQUENT VISITS Part 02 PRENATAL CARE : SUBSEQUENT VISITS Part 02 Reviewed by Radiology Madeeasy on December 27, 2010 Rating: 5
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