Down’s syndrome and trisomies- meiotic non-disjunction

Major organ abnormality or 2 more minor increased risk fetal aneuploidy

Amniocentesis 15-20 weeks (accuracy > 99%)

  • Loss rate 1in 300-500
  • Vagina spotting/leakage 1-2% (perinatal survival after leak 90% seals)
  • Chorioamnionitis < 1%
  • Early amino 11-13 weeks- high preg loss rate 2-5% talipes 1.4% (Early amino should not be done better than CVS)

CVS after 9 completed weeks. Placental villi transcervical/abdominal (no difference in loss rate) increased risk limb defects if done before 9 weeks

Culdocentesis- percutaneous umbilical blood sampling vein loss rate < 2%


Increased risk for aneuploidy

  1. Previous child/fetus trisomy risk 1.6-8.2%
  2. Structural anomalies by U/S (1 major, 2 minor)
  3. Previous fetus/child sex chromosome abnormality (4xyy extra chromosome paternal not maternal no increased risk)
  4. Paternal carrier chromosome translocation, women and men balanced translocation
  5. Paternal carrier chromo inversion (2 breaks occur same chromosome. Depending on chromo involved and size. Exception pericentric inversion chromosome 9 common variant general population)
  6. Paternal aneuploidy/mosaicism
  • Female T-21 50% risk child T-21
  • Female 47XXX & men 47XYY are fertile. No increased risk of trisomic offspring

Men normal karotype who have oligospermia or ICSI increased incidence of abnormal karyotype in sperm.


  1. Cultured amniocytes or CV cells results 1-2 weeks