amniocentesis

The main indications for amniocentesis are for
chromosomal analysis of cultured amniotic cells in
pregnancies at increased risk of Down syndrome or other
chromosomal abnormalities and for estimating fetoprotein
concentration and acetylcholinesterase activity in amniotic
fluid in pregnancies at increased risk of neural tube defects,
although few amniocenteses are now done for neural tube
defects because of improved detection by ultrasonography.
In specific cases biochemical analysis of amniotic fluid or
cultured cells may be required for diagnosing inborn errors
of metabolism. Tests on amniotic fluid usually yield results
within 7–10 days, whereas those requiring cultured cells may
take around 2–4 weeks. Results may not be available until
18 weeks’ gestation or later, leading to late termination in
affected cases.