Amniocentesis

Amniocentesis is a well established and widely available method
for prenatal diagnosis. It is usually performed at 15 to 16 weeks’
gestation but can be done a few weeks earlier in some cases. It
is reliable and safe, causing an increased risk of miscarriage of
around 0.5–1.0%. Amniotic fluid is aspirated directly, with or
without local anaesthesia, after localisation of the placenta by
ultrasonography. The fluid is normally clear and yellow and
contains amniotic cells that can be cultured. Contamination of
the fluid with blood usually suggests puncture of the placenta
and may hamper subsequent analysis. Discoloration of the fluid
may suggest impending fetal death.