Why it is done
The amniotic fluid contains cells and chemicals from the fetus that can be analyzed to detect abnormalities,such as down's syndrome and other chromosomal abnormalities.Amniocentesis can also detect genetic disorders (such as hemophilia,cystic fibrosis,and Tay-sachs disease),or
development disorders (such as spina bifida).It is also used to assess fetal disorders,such as rhesus incompatibility,and to check the maturity of fetal lungs.
How it is done
Amniocentesis is usually performed between the 16th and 18th week of gestation.Ultrasound scanning is used to estimate the age and position of the fetus,the placental site,and the amount of amniotic fluid A needle is then inserted through the abdomen and uterine wall into the amniotic sac,avoiding the fetus and placenta.A syringe is attached to the needle and about 20 to 30 ml of fluid is removed for analysis. Anesthesia is not usually required,although occasionally a local anesthetic is used.In most cases, the woman can go home soon after the procedure but is advise to rest foe about 24 hrs.
Results
The amniotic fluid is analyzed bio chemically and fetal cells are cultured for chromosomal analysis.Culturing cells for Chromosomal analysis may take up to four weeks and results may there fore not be available until 20 weeks' gestation As well as identifying fetal disorders, chromosome analysis revels the sex of the fetus.A woman should therefore indicate whether or not she wishes to receive this information.Some laboratories do not report the sex of the fetus.
Complication
There is a slightly increased incidence of miscarriage oe early rapture of the membranes after amniocentesis;recent studies show a risk of about 0.5%. Amniocentesis is therefore usually recommended only for women over the age of 35 (who more likely to have child with Down's
syndrome),or when there are other compelling medical reasons,such as family history of chromosomal abnormalities.
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