The definitive diagnosis of chromosomal disorders can only be made by examining the fetal cells. After 10 weeks of gestation, biopsy of the placenta - Chorionic Villus Sampling (CVS) or amniocentesis after the 16th week are the methods used.

 

CVS ( Chorionic Villus Sampling)

 

The placenta has the  same chromosomal structure with the fetus. Therefore, chromosome analysis of placenta also represents the fetus. CVS can be performed after 10 weeks. Compared  to amniocentesis, it is possible to obtain the results  4-6 weeks earlier. CVS would be useful especially for  the investigation of known genetic diseases, in patients with positive combined secreening , presence of significantly increased nuchal translucency  and abnormal structural findings.

The procedure is performed with a slightly thicker needle than the amniocentesis because some tissue is taken. Therefore, the skin and subcutaneous tissues are infiltrated with local anesthesia first. But since it is not possible to inject local anesthetic into  the uterine wall, there may be a slight burning sensation during the procedure. The abortion  rate following the procedure  is roughly 1%.

 

Amniocenthesis

• With the help of a long thin needle, amniotic fluid around the fetus is obtained through maternal abdominal wall.  The ideal period for amniocenthesis  is after the 16th weeks of pregnancy. Earlier procedures may cause some orthopedic problems in infants. Approximately 15-20 ml of fluid is taken. There are free-floating fetal cells in the amniotic fluid. These cells are separated and grown in cell culture. When these cells multiply and reach a certain number, chromosomes are extracted and analysed. This process takes 2 weeks. In addition, it might be useful in the diagnosis of some intrauterine infections that might affect the fetus and to decrease the amount of fluid around the fetus in case of polyhydramnios. 

 

 

• Amniocentesis is performed under the continuous ultrasound guidance with a very thin needle.  It is a very rare complication that the baby is injured during the procedure.

• One-tenth of the fluid around the fetus and is reproduced within a few hours. For this reason, there is always enough fluid around the baby

• 1% of patients undergoing amniocentesis may have mild bleeding and water passage, vaginally. This often does not result in a miscarriage and is spontaneously heals.

• Bleeding, severe pain, fever, water passage are the main reasons to call your doctor.

• No strict bed rest is required after the procedure. I advise to have a quiet day preferably at home on the day of procedure. From the next day you can return to daily life.

• Amniocentesis is associated with an abortion risk which is between  one to two hundred and four hundred (1: 200-1: 400). Our main goal is to diagnose the fetuses with chromosomal disorders, meanwhile to  minimize the procedure related healthy fetal losses. If we perform amniocentesis to every pregnant woman, we can loose  4-5 healthy fetuses to diagnose a fetus with Down syndrome.
   

• Amniocenteses is recommended for high risk women for chromosomal abnormalities (Risk Positive Group).  

1. Age: Numerical chromosomal disorders increase with age. Advanced maternal age may be an indication for amniocentesis. But especially in pregnant women under 40 years of age, it is advised to carry screening tests first and do amniocenthesis to those who are screen positive. After  40 years of age, screening tests or direct amniocentesis should be discussed with the couple.

2-   Being in high risk group as aresult of  screening tests

3-   Suspicious ultrasound findings for chromosomal disorders and  genetic diseases.

4 -  Positive findings in Cell-free Fetal DNA analysis in maternal blood