Screening tests are different from diagnostic tests. Screening tests tell you whether your chance of having a baby with a problem is increased or decreased. Diagnostic tests tell you for sure if there is a problem. If you want to know for sure, then you should consider CVS or amniocentesis, which are diagnostic tests. The benefit of these testing options is that they can provide a “yes” or “no” answer rather than risk assessment for a pregnancy. However, because these are invasive procedures, there is a very slight risk for complications.
What Are Chromosome Abnormality?
Most chromosome abnormalities are not inherited, but happen when, by chance, the egg or sperm receives an extra chromosome before conception. The most common chromosome abnormalities involve chromosomes 13, 18 or 21. There are no cures for the chromosomes abnormalities but there are some treatments available to improve quality of life. However, many babies with chromosome abnormalities are miscarried early in the pregnancy.
Down syndrome, also called trisomy 21, is caused by an extra copy of chromosome 21. People with Down syndrome share some distinct physical traits and facial features. Related medical conditions or birth defects include mental impairment.
If an extra copy of chromosomes 13 or 18 is present (trisomy 13 or 18), by the baby will have mental retardation in the severe range and will likely not survive past the first few weeks of life.
What Are The Risk Factors?
Every woman is at some risk to have a baby with a chromosome abnormality. The risk increases with the increasing age of the mother. Other risk factors include a multiple pregnancy, a previous pregnancy with chromosome abnormality or a parental chromosome abnormality.
Chorionic Villus Sampling (CVS)
WHAT IT IS
Chorionic villus sampling (or CVS) is a type of diagnostic procedure, where a small sample of the placenta is removed for testing. It is generally performed between 10 and 14 weeks of your pregnancy. Although the procedure is very safe, because it is an invasive test, there is a small risk of miscarriage (less than a 0.005% risk) associated with CVS.
HOW IT’S DONE
There are two methods for performing the CVS: transabdominal and transcervical. The method will be selected by physician following a thorough ultrasound where the placental location is identified and used to determine the easiest and safest of the two procedures.
In the transabdominal method, a thin needle is inserted into the lower part of the abdomen below the navel. During the procedure, we watch with ultrasound to guide the needle through the abdomen into the placenta to perform the placental biopsy.
In the transcervical method, a thin catheter is inserted through the cervix into the uterus. Again, the method utilizes the ultrasound monitor to guide the catheter into the placenta.
With either method, it is expected that you will experience some discomfort during the procedure, however, most women describe the CVS as more uncomfortable than painful. After you have this procedure, we recommend that you avoid any heavy lifting or strenuous activity for 24-48 hours. It can be normal to experience a small amount of bleeding and mild cramping after the procedure.
WHY IT’S DONE
There are a number of reasons to consider CVS. It could be because or your age, family history, an ultrasound finding, an abnormal screening test or simply because you want more information. If a diagnosis is known beforehand, it can help the doctors make sure the medical team is ready to go.
CVS, is a diagnostic test and tells you whether the baby has a genetic chromosome problem such as Down syndrome or trisomy 18. Also, like amniocenteses, additional DNA testing can be performed on the placental sample if, based upon your family history or other factors, there is an increased risk for other genetic conditions. Chromosome results are available in two weeks or less.
WHAT IT IS
Amniocentesis is a diagnostic genetic test that is performed after 15 weeks of pregnancy. Although the procedure is very safe, because it is an invasive test, there is a small risk of miscarriage (less than a 0.002% risk) associated with amniocentesis.
HOW IT’S DONE
A long thin needle is inserted into the lower part of the abdomen below the navel. During the amniocentesis procedure, we watch with ultrasound to make sure the needle stays in a safe pocket of fluid, away from the baby. A small amount of fluid is removed, which contains living cells that have been shed from the baby. It is expected that you will experience some discomfort during the procedure, however, most women describe the amniocentesis as more uncomfortable than painful. After you have an amniocentesis, we recommend that you avoid any strenuous activity for the rest of the day and refrain from flying for 72 hours. It can be normal to experience mild cramping after the procedure.
WHY IT’S DONE
There are a number of reasons to consider amniocentesis. It could be because of your age, family history, an ultrasound finding, an abnormal blood test or simply because you want more information. Amniocentesis is a diagnostic test which tells you whether the baby has a genetic chromosome condition such as Down syndrome or trisomy 18. Results are available in two weeks or less.