1. FETAL MEMBRANES IN HUMAN
The fetal membranes, or chorioamniotic membranes, which surround and protect a developing fetus ,,,,  Amnion 

2. In the human embryo
In the human embryo, in the fourth or fifth week amniotic fluid (also called liquor amnii) begins to accumulate within it.
The amniotic fluid increases in quantity up to the sixth or seventh month of pregnancy, after which it diminishes somewhat; at the end of pregnancy it amounts to about 1 liter.
The amniotic fluid allows the free movements of the fetus during the later stages of pregnancy, and also protects it by diminishing the risk of injury from without.
It contains less than two percent solids consisting of urea and other extractives, inorganic salts, a small amount of protein, and frequently of sugar.

3. Amniocentesis
Amniocentesis (also referred to as amniotic fluid test or (AFT)
is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, and also used for sex determination in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amniotic sac surrounding a developing fetus, than the fetal DNA is examined ,by extracted of DNA from the amniotic cells by sequential centrifugation and analysed using the polymerase chain reaction (PCR).
The most common abnormalities detected are:-
Down syndrome (trisomy 21).
Edwards syndrome (trisomy 18).
Turner syndrome (monosomy X).

4. Down syndrome (trisomy 21). Edwards syndrome (trisomy 18)
Down syndrome (trisomy 21) Edwards syndrome (trisomy 18) Turner syndrome (monosomy X).

6. What Can be Detected by an Amniocentesis?
Woman who will be 35 years old or more at time of delivery.
Couple with a child or other family member with a chromosomal abnormality such as Down syndrome.
Couple in which one partner has a chromosomal rearrangement (for example, a translocation or an inversion).
Couple with an increased risk of having a child with a genetic disease for which testing is available.
Couple with a previous pregnancy or child with a neural tube defect (for example, spina bifida or anencephaly by measurement of the AFP protein

7. Procedure
Before the start of the procedure, a local anesthetic can be given to the mother in order to relieve the pain felt during the insertion of the needle used to withdraw the fluid.
After the local anesthetic is in effect, a needle is usually inserted through the mother’s abdominal wall, then through the wall of the uterus, and finally into the amniotic sac. With the aid of ultrasound-guidance, a puncture of the sac in an area away from the fetus and extracts approximately 20ml of amniotic fluid.
The fetal cells are separated from the extracted sample. The cells are grown in a culture medium, then fixed and stained. Under a microscope the chromosomes are examined for abnormalities.

9. Procedure

12. Symptoms
Cramping that does not resolve with bed rest, is severely painful, or that occurs at regular intervals for one hour or more.
Clear, watery vaginal discharge or vaginal bleeding. Occasionally, a woman may leak a small amount of clear fluid. Bleeding is not common following amniocentesis.
Fever of °F or 38 °C.
Any changes with pregnancy that are of concern.

13. Complications of amniocentesis include :-
preterm labor and delivery.
respiratory distress,
postural deformities.
Chorioamnionitis.
fetal trauma

14. Risks Associated with an Amniocentesis
Mild leakage of a small amount of clear fluid (amniotic) may occur. As with all invasive procedures, infection is a risk.
There is a natural apportion rate throughout pregnancy. An amniocentesis increases the natural rate of apportion. The most recent data shows that about 1 in 1,600 women may have a apportion as a result of amniocentesis